Vulnerability-Lookup

PYSEC-2026-2527

Vulnerability from pysec - Published: 2026-07-13 14:36 - Updated: 2026-07-13 16:04

Details

Impact

This is a stored Cross-Site Scripting (XSS) vulnerability affecting the website and author comment fields. The website field was HTML-escaped using quote=False, which left single and double quotes unescaped. Since the frontend inserts the website value directly into a single-quoted href attribute via string concatenation, a single quote in the URL breaks out of the attribute context, allowing injection of arbitrary event handlers (e.g. onmouseover, onclick).

The same escaping was missing entirely from the user-facing comment edit endpoint (PUT /id/) and the moderation edit endpoint (POST /id//edit/).

Any visitor to a page embedding isso comments is impacted. No authentication or interaction beyond mouse movement is required to trigger a payload — an attacker can post a comment anonymously (moderation is off by default) with a crafted website URL, and the payload persists in the database and fires on every page load. With the full-page invisible overlay technique described in the report, the victim only needs to move their mouse.

Patches

The issue is fixed in commit 3cf27c2. Users should upgrade to a version containing that commit once released. The fix applies html.escape(..., quote=True) to the website field across all three write paths (POST /new, PUT /id/, POST /id//edit/), and adds input validation and escaping to the moderation edit endpoint which previously had neither.

Workarounds

Enabling comment moderation (moderation = enabled = true in isso.cfg) prevents unauthenticated users from publishing comments, raising the bar for exploitation. However, it does not fully mitigate the issue since a moderator activating a malicious comment would still expose visitors. There is no configuration-only workaround that fully prevents the vulnerability.

Resources

https://docs.python.org/3/library/html.html#html.escape — note the quote parameter

Severity

6.1 (Medium)


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

Impacted products

Name	purl
isso	pkg:pypi/isso

Aliases

JSON

To clipboard

{
  "affected": [
    {
      "package": {
        "ecosystem": "PyPI",
        "name": "isso",
        "purl": "pkg:pypi/isso"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "0.13.2"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "0.10",
        "0.10.1",
        "0.10.2",
        "0.10.3",
        "0.10.4",
        "0.10.5",
        "0.10.6",
        "0.11.0",
        "0.11.1",
        "0.12.0",
        "0.12.1",
        "0.12.2",
        "0.12.4",
        "0.12.5",
        "0.12.6",
        "0.12.6.1",
        "0.12.6.2",
        "0.13.0",
        "0.13.1.dev0",
        "0.8",
        "0.8.1",
        "0.8.2",
        "0.8.3",
        "0.9",
        "0.9.1",
        "0.9.10",
        "0.9.2",
        "0.9.3",
        "0.9.4",
        "0.9.5",
        "0.9.6",
        "0.9.7",
        "0.9.8",
        "0.9.9"
      ]
    }
  ],
  "aliases": [
    "CVE-2026-27469",
    "GHSA-9fww-8cpr-q66r"
  ],
  "details": "## Impact\n\nThis is a stored Cross-Site Scripting (XSS) vulnerability affecting the website and author comment fields. The website field was HTML-escaped using quote=False, which left single and double quotes unescaped. Since the frontend inserts the website value directly into a single-quoted href attribute via string concatenation, a single quote in the URL breaks out of the attribute context, allowing injection of arbitrary event handlers (e.g. onmouseover, onclick).\n\nThe same escaping was missing entirely from the user-facing comment edit endpoint (PUT /id/\u003cid\u003e) and the moderation edit endpoint (POST /id/\u003cid\u003e/edit/\u003ckey\u003e).\n\nAny visitor to a page embedding isso comments is impacted. No authentication or interaction beyond mouse movement is required to trigger a payload \u2014 an attacker can post a comment anonymously (moderation is off by default) with a crafted website URL, and the payload persists in the database and fires on every page load. With the full-page invisible overlay technique described in the report, the victim only needs to move their mouse.\n\n## Patches\n\nThe issue is fixed in commit 3cf27c2. Users should upgrade to a version containing that commit once released. The fix applies html.escape(..., quote=True) to the website field across all three write paths (POST /new, PUT /id/\u003cid\u003e, POST /id/\u003cid\u003e/edit/\u003ckey\u003e), and adds input validation and escaping to the moderation edit endpoint which previously had neither.\n\n## Workarounds\n\n  Enabling comment moderation (moderation = enabled = true in isso.cfg) prevents unauthenticated users from publishing comments, raising the bar for exploitation. However, it\n  does not fully mitigate the issue since a moderator activating a malicious comment would still expose visitors. There is no configuration-only workaround that fully prevents\n   the vulnerability.\n\n## Resources\n\n  - https://docs.python.org/3/library/html.html#html.escape \u2014 note the quote parameter",
  "id": "PYSEC-2026-2527",
  "modified": "2026-07-13T16:04:21.211428Z",
  "published": "2026-07-13T14:36:38.311279Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/isso-comments/isso/security/advisories/GHSA-9fww-8cpr-q66r"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-27469"
    },
    {
      "type": "WEB",
      "url": "https://github.com/isso-comments/isso/commit/0afbfe0691ee237963e8fb0b2ee01c9e55ca2144"
    },
    {
      "type": "WEB",
      "url": "https://docs.python.org/3/library/html.html#html.escape"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/isso-comments/isso"
    },
    {
      "type": "PACKAGE",
      "url": "https://pypi.org/project/isso"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/advisories/GHSA-9fww-8cpr-q66r"
    }
  ],
  "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": "Isso affected by Stored XSS via comment website field"
}

CVE-2026-27469 (GCVE-0-2026-27469)

Vulnerability from cvelistv5 – Published: 2026-02-21 07:24 – Updated: 2026-02-24 18:50

Title

Isso: Stored XSS via comment website field

Summary

Isso is a lightweight commenting server written in Python and JavaScript. In commits before 0afbfe0691ee237963e8fb0b2ee01c9e55ca2144, there is a stored Cross-Site Scripting (XSS) vulnerability affecting the website and author comment fields. The website field was HTML-escaped using quote=False, which left single and double quotes unescaped. Since the frontend inserts the website value directly into a single-quoted href attribute via string concatenation, a single quote in the URL breaks out of the attribute context, allowing injection of arbitrary event handlers (e.g. onmouseover, onclick). The same escaping is missing entirely from the user-facing comment edit endpoint (PUT /id/) and the moderation edit endpoint (POST /id//edit/). This issue has been patched in commit 0afbfe0691ee237963e8fb0b2ee01c9e55ca2144. To workaround, nabling comment moderation (moderation = enabled = true in isso.cfg) prevents unauthenticated users from publishing comments, raising the bar for exploitation, but it does not fully mitigate the issue since a moderator activating a malicious comment would still expose visitors.

Severity

6.1 (Medium)


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

SSVC

Exploitation: none Automatable: no Technical Impact: partial

CISA Coordinator (v2.0.3)

CWE

CWE-79 - Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
CWE-116 - Improper Encoding or Escaping of Output

Assigner

GitHub_M

References

3 references

URL	Tags
https://github.com/isso-comments/isso/security/ad…	x_refsource_CONFIRM
https://github.com/isso-comments/isso/commit/0afb…	x_refsource_MISC
https://docs.python.org/3/library/html.html#html.escape	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version
isso-comments	isso	Affected: < 0afbfe0691ee237963e8fb0b2ee01c9e55ca2144

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2026-27469",
                "options": [
                  {
                    "Exploitation": "none"
                  },
                  {
                    "Automatable": "no"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-02-24T18:49:50.634395Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2026-02-24T18:50:07.650Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "product": "isso",
          "vendor": "isso-comments",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 0afbfe0691ee237963e8fb0b2ee01c9e55ca2144"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "Isso is a lightweight commenting server written in Python and JavaScript. In commits before 0afbfe0691ee237963e8fb0b2ee01c9e55ca2144, there is a stored Cross-Site Scripting (XSS) vulnerability affecting the website and author comment fields. The website field was HTML-escaped using quote=False, which left single and double quotes unescaped. Since the frontend inserts the website value directly into a single-quoted href attribute via string concatenation, a single quote in the URL breaks out of the attribute context, allowing injection of arbitrary event handlers (e.g. onmouseover, onclick). The same escaping is missing entirely from the user-facing comment edit endpoint (PUT /id/) and the moderation edit endpoint (POST /id//edit/). This issue has been patched in commit 0afbfe0691ee237963e8fb0b2ee01c9e55ca2144. To workaround, nabling comment moderation (moderation = enabled = true in isso.cfg) prevents unauthenticated users from publishing comments, raising the bar for exploitation, but it does not fully mitigate the issue since a moderator activating a malicious comment would still expose visitors."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "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"
          }
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-79",
              "description": "CWE-79: Improper Neutralization of Input During Web Page Generation (\u0027Cross-site Scripting\u0027)",
              "lang": "en",
              "type": "CWE"
            }
          ]
        },
        {
          "descriptions": [
            {
              "cweId": "CWE-116",
              "description": "CWE-116: Improper Encoding or Escaping of Output",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-02-21T07:24:38.971Z",
        "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
        "shortName": "GitHub_M"
      },
      "references": [
        {
          "name": "https://github.com/isso-comments/isso/security/advisories/GHSA-9fww-8cpr-q66r",
          "tags": [
            "x_refsource_CONFIRM"
          ],
          "url": "https://github.com/isso-comments/isso/security/advisories/GHSA-9fww-8cpr-q66r"
        },
        {
          "name": "https://github.com/isso-comments/isso/commit/0afbfe0691ee237963e8fb0b2ee01c9e55ca2144",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/isso-comments/isso/commit/0afbfe0691ee237963e8fb0b2ee01c9e55ca2144"
        },
        {
          "name": "https://docs.python.org/3/library/html.html#html.escape",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://docs.python.org/3/library/html.html#html.escape"
        }
      ],
      "source": {
        "advisory": "GHSA-9fww-8cpr-q66r",
        "discovery": "UNKNOWN"
      },
      "title": "Isso: Stored XSS via comment website field"
    }
  },
  "cveMetadata": {
    "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
    "assignerShortName": "GitHub_M",
    "cveId": "CVE-2026-27469",
    "datePublished": "2026-02-21T07:24:38.971Z",
    "dateReserved": "2026-02-19T17:25:31.101Z",
    "dateUpdated": "2026-02-24T18:50:07.650Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

GHSA-9FWW-8CPR-Q66R

Vulnerability from github – Published: 2026-02-24 16:03 – Updated: 2026-02-24 16:03

Summary

Isso affected by Stored XSS via comment website field

Details

Impact

The same escaping was missing entirely from the user-facing comment edit endpoint (PUT /id/) and the moderation edit endpoint (POST /id//edit/).

Patches

Workarounds

Resources

https://docs.python.org/3/library/html.html#html.escape — note the quote parameter

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": [
    {
      "package": {
        "ecosystem": "PyPI",
        "name": "isso"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "0.13.2"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-27469"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-116",
      "CWE-79"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-02-24T16:03:04Z",
    "nvd_published_at": "2026-02-21T08:16:11Z",
    "severity": "MODERATE"
  },
  "details": "## Impact\n\nThis is a stored Cross-Site Scripting (XSS) vulnerability affecting the website and author comment fields. The website field was HTML-escaped using quote=False, which left single and double quotes unescaped. Since the frontend inserts the website value directly into a single-quoted href attribute via string concatenation, a single quote in the URL breaks out of the attribute context, allowing injection of arbitrary event handlers (e.g. onmouseover, onclick).\n\nThe same escaping was missing entirely from the user-facing comment edit endpoint (PUT /id/\u003cid\u003e) and the moderation edit endpoint (POST /id/\u003cid\u003e/edit/\u003ckey\u003e).\n\nAny visitor to a page embedding isso comments is impacted. No authentication or interaction beyond mouse movement is required to trigger a payload \u2014 an attacker can post a comment anonymously (moderation is off by default) with a crafted website URL, and the payload persists in the database and fires on every page load. With the full-page invisible overlay technique described in the report, the victim only needs to move their mouse.\n\n## Patches\n\nThe issue is fixed in commit 3cf27c2. Users should upgrade to a version containing that commit once released. The fix applies html.escape(..., quote=True) to the website field across all three write paths (POST /new, PUT /id/\u003cid\u003e, POST /id/\u003cid\u003e/edit/\u003ckey\u003e), and adds input validation and escaping to the moderation edit endpoint which previously had neither.\n\n## Workarounds\n\n  Enabling comment moderation (moderation = enabled = true in isso.cfg) prevents unauthenticated users from publishing comments, raising the bar for exploitation. However, it\n  does not fully mitigate the issue since a moderator activating a malicious comment would still expose visitors. There is no configuration-only workaround that fully prevents\n   the vulnerability.\n\n## Resources\n\n  - https://docs.python.org/3/library/html.html#html.escape \u2014 note the quote parameter",
  "id": "GHSA-9fww-8cpr-q66r",
  "modified": "2026-02-24T16:03:04Z",
  "published": "2026-02-24T16:03:04Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/isso-comments/isso/security/advisories/GHSA-9fww-8cpr-q66r"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-27469"
    },
    {
      "type": "WEB",
      "url": "https://github.com/isso-comments/isso/commit/0afbfe0691ee237963e8fb0b2ee01c9e55ca2144"
    },
    {
      "type": "WEB",
      "url": "https://docs.python.org/3/library/html.html#html.escape"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/isso-comments/isso"
    }
  ],
  "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": "Isso affected by Stored XSS via comment website field"
}

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

PYSEC-2026-2527

Impact

Patches

Workarounds

Resources

CVE-2026-27469 (GCVE-0-2026-27469)

GHSA-9FWW-8CPR-Q66R

Impact

Patches

Workarounds

Resources

Tags

Sightings

Nomenclature