DOMPurify: SMIL attributeName=href guard is skipped when PARSER_MEDIA_TYPE is application/xhtml+xml

{
  "id": "22573a4e0913204aea40ddea79ecf93033a882fefc51e7cd90239eccd922b570",
  "url": "https://osv.dev/vulnerability/GHSA-c6gr-qvv4-5v3f",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "DOMPurify: SMIL attributeName=href guard is skipped when PARSER_MEDIA_TYPE is application/xhtml+xml",
    "summary": "### Summary DOMPurify drops `attributeName` attributes whose value contains `href`, so an allowed `` or `` can't rewrite a link's href after sanitizing. The check compares the attribute name after `transformCaseFunc`, and that function doesn't lowercase in XHTML mode. In XHTML the attribute is spelled `attributeName`, so the comparison with `\"attributename\"` never matches and the guard does nothing. An app that uses `PARSER_MEDIA_TYPE: 'application/xhtml+xml'` and allows `animate` and `attributeName` will keep ``. Clicking the parent link then runs the script. This needs a non-default config, so going by SECURITY.md, this is a hardening bug rather than a bypass of the default config. ### Details In `_sanitizeAttributes` (dist/purify.js line 2216 in 3.4.16): ```js const lcName = transformCaseFunc(name); ... if (lcName === \"attributename\" && stringMatch(value, \"href\")) { _removeAttribute(name, currentNode, attr); continue; } ``` `transformCaseFunc` is `stringToLowerCase` for text/html but the identity function for application/xhtml+xml, because XML names are case-sensitive. The XML parser keeps SVG's real name `attributeName`, so in XHTML mode `lcName` is `attributeName` and the branch never runs. People using XHTML mode have to list SVG attributes in camelCase. The built-in attribute lists are lowercase and won't match, so `ALLOWED_ATTR`/`ADD_ATTR: ['attributeName', ...]` is the config you'd naturally write here. The value also passes the URI check. `IS_ALLOWED_URI` only check",
    "evidence": "osv:GHSA-c6gr-qvv4-5v3f",
    "products": [
      {
        "name": {
          "value": "dompurify",
          "evidence": "/affected/0/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "3.4.17",
            "evidence": "/affected/0/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "low",
    "structured": {
      "id": "GHSA-c6gr-qvv4-5v3f",
      "aliases": [
        "CVE-2026-116802",
        "GHSA-c6gr-qvv4-5v3f"
      ],
      "affected": [
        {
          "ranges": [
            {
              "type": "SEMVER",
              "events": [
                {
                  "introduced": "0"
                },
                {
                  "fixed": "3.4.17"
                }
              ]
            }
          ],
          "package": {
            "name": "dompurify",
            "purl": "pkg:npm/dompurify",
            "ecosystem": "npm"
          },
          "database_specific": {
            "source": "https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/10/GHSA-c6gr-qvv4-5v3f/GHSA-c6gr-qvv4-5v3f.json",
            "last_known_affected_version_range": "<= 3.4.16"
          }
        }
      ],
      "modified": "2026-10-27T10:56:08.682782458Z",
      "provider": "osv",
      "references": [
        "https://github.com/cure53/DOMPurify/security/advisories/GHSA-c6gr-qvv4-5v3f",
        "https://github.com/cure53/DOMPurify/pull/1672",
        "https://github.com/cure53/DOMPurify/commit/a77a3e78b59f72fa4d1c83f22e121ad9cc7d3575",
        "https://github.com/cure53/DOMPurify",
        "https://github.com/cure53/DOMPurify/releases/tag/3.4.17"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-79"
        ],
        "severity": "LOW",
        "github_reviewed": true,
        "nvd_published_at": null,
        "github_reviewed_at": "2026-10-22T16:24:23Z"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-116802",
        "evidence": "/aliases"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/database_specific/severity"
  },
  "source_id": "core-osv",
  "document_id": 461504,
  "published_at": "2026-10-22T16:24:23+00:00"
}