GHSA-6688-9rhm-gjv2: DOMPurify Remote Code Execution Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-6688-9rhm-gjv2",
  "modified" : "2026-10-05T23:43:53Z",
  "published" : "2026-10-05T23:43:53Z",
  "aliases" : [ ],
  "summary" : "DOMPurify: IN_PLACE returns a force-removed rawtext root whose text carries attacker markup — pure HTML reparse executes",
  "details" : "## Environment\n\n- dompurify 3.4.15 (current npm release); reproduced independently on jsdom 30.0.1 and 29.1.1 (Node.js 20.x / 26.x)\n- Config: `DOMPurify.sanitize(node, { IN_PLACE: true })` on a Node input; `SAFE_FOR_XML` at its default (`true`)\n\n## Summary\n\nThe 3.4.9 fix for the IN_PLACE detached-root class added two protections on the IN_PLACE return path: a fail-closed `TypeError` in `_forceRemove` when a node selected for removal cannot be detached, and a `_neutralizeSubtree` pass (`dist/purify.js` line 1336) that strips non-allowlisted **attributes** from removed subtrees.\n\nBoth miss the rawtext **text-content** form. When the force-removed root is a rawtext element (`<style>`), the payload lives in the node's *text*: the node detaches fine (the `TypeError` guard is not reached), `_neutralizeSubtree` strips nothing (there are no attributes), and the IN_PLACE exit returns the detached, never-sanitized `<style>` whose text still carries live markup. Serializing that node and re-parsing it in **plain HTML context** materializes the payload — no foreign-content context required.\n\nThe same Node input sanitized **without** `IN_PLACE` returns an empty result: the only difference is the IN_PLACE return path handing the killed node back.\n\n## Steps to reproduce\n\n```js\nconst { JSDOM } = require('jsdom');\nconst createDOMPurify = require('dompurify');   // 3.4.15\n\nconst window = new JSDOM('').window;\nconst DOMPurify = createDOMPurify(window);\n\nconst styleRoot = window.document.createElement('style');\nstyleRoot.setAttribute('onclick', 'alert(1)');    // attribute payload\nstyleRoot.textContent = '</style><img src=x onerror=1>';  // text payload\nwindow.document.body.appendChild(styleRoot);\n\nconst returned = DOMPurify.sanitize(styleRoot, { IN_PLACE: true });\n\nconsole.log(returned === styleRoot);                       // true (same node)\nconsole.log(styleRoot.parentNode === null);                // true (detached)\nconsole.log(styleRoot.outerHTML);\n// <style></style><img src=x onerror=1></style>\nconsole.log(styleRoot.getAttribute('onclick'));            // null  (attribute neutralized)\nconsole.log(styleRoot.textContent);                        // '</style><img src=x onerror=1>' (text survives)\n\n// plain HTML reparse (no foreign-content context involved):\nconst probe = window.document.createElement('div');\nprobe.innerHTML = returned.outerHTML || styleRoot.outerHTML;\nconsole.log(probe.querySelectorAll('img').length);         // 1\nconsole.log(probe.querySelector('img').getAttribute('onerror')); // \"1\"\n```\n\nObserved on 3.4.15: one node, one call — the `onclick` **attribute** is neutralized while the **text** payload (`</style><img src=x onerror=1>`) survives verbatim; serializing and re-parsing the returned node in plain HTML context materializes the `img` with the live `onerror` handler.\n\nContrast on the same Node input without `IN_PLACE`: `RETURN_DOM: true` → `<body></body>`; `RETURN_DOM_FRAGMENT: true` → 0 children — the payload is fully sanitized away. The only difference is the IN_PLACE return path.\n\nContrast on the removal trigger: `SAFE_FOR_XML: false` → the node is not removed (detached stays false); plain CSS text → not removed. The removal is gated by the mXSS text probes and happens *specifically because* the serialized node would re-open tags on reparse.\n\n## Root cause\n\n`_isUnsafeNode` (`dist/purify.js` 3.4.15, lines 1700–1714) removes nodes whose literal text would re-open tags on reparse — shape (b) in the source comment is \"text-only content that already carries the element's OWN end tag\", detected by the `LITERAL_TEXT_CLOSE` probe (line 385) alongside the `ELEMENT_MARKUP_PROBE` (line 339) rules. `_forceRemove` (line 1122) records the node in `DOMPurify.removed` (`{element}`) and detaches it. The removal is intentional: the upstream comment states these shapes are removed **because the literal serializer emits them verbatim for the HTML parser to re-open**.\n\nThe IN_PLACE exit then hands the force-removed root back to the caller — the very node whose removal `DOMPurify.removed` just recorded (verified: `DOMPurify.removed.some(e => e.element === root)` is `true` on the returned instance). The 3.4.9 `_neutralizeSubtree` pass (line 1336) addresses only the attribute form — its own docstring: \"walks a removed subtree and strips every attribute\" (purpose: cancel queued resource events). Rawtext text content is out of its scope, so the removal that was performed *specifically to prevent reparse* is undone by returning the node: you removed it to stop the reparse, then returned it.\n\nDifferential (one node, one call, same removal path): the `onclick` attribute is neutralized by the existing pass while the text payload survives verbatim — the attribute axis is covered, the text axis is the gap.\n\n## Impact\n\nIdentical blast radius to the published IN_PLACE family: an application that sanitizes a Node in `IN_PLACE` mode and re-inserts (or serializes and then re-inserts) the result materializes attacker markup in plain HTML context: script execution in the page. Moving the returned node via `appendChild` alone is safe; the round trip through serialization is what fires the payload. No foreign-content context is required with the close-tag payload.\n\n## Affected versions\n\n- Verified live: 3.4.15 (current).\n- Source-verified: the attribute-only `_neutralizeSubtree` and the IN_PLACE return path are present in 3.4.9–3.4.14; releases before 3.4.9 predate the fix entirely (unconditional return; individual pre-3.4.9 releases not dynamically tested).\n- Per cure53 advisory convention the affected range is reported as `<= 3.4.15` (current at time of writing).\n\n## Suggested remediation\n\n**Primary (root-cause, covers every form):** at the IN_PLACE exit, check whether the returned root was recorded during sanitization — `DOMPurify.removed.some(e => e.element === root)` — and fail closed: throw the same `TypeError` style used by the 3.4.9 detach guard (\"a node selected for removal could not be safely returned; refusing to sanitize in place\"), or return `null`. This is consistent with the existing fail-closed design and covers all present and future root-kill reasons in one check.\n\n**Secondary (form-specific):** extend `_neutralizeSubtree` to neutralize **text content of rawtext descendants** — the elements in `LITERAL_TEXT_ELEMENT_NAMES` (`style`, `script`, `xmp`, `iframe`, `noembed`, `noframes`, `plaintext`, `noscript`) — by rewriting `textContent` to a defanged form, matching the probe coverage of `_isUnsafeNode`/`LITERAL_TEXT_CLOSE`.\n\nA regression test asserting that a force-removed rawtext root comes back with no `/<[/\\w!]/` match in `textContent` (and is not returned at all under the primary fix) prevents re-introduction.\n\n## Prior art / differentiation\n\n- GHSA-r47g-fvhr-h676 (fixed 3.4.6): clobbered-form **root** removal — different trigger; this report's root is a normal allowlisted `style` element killed by the text probe.\n- GHSA-55q2-fjhq-7xh7 (low): IN_PLACE **hook removal** leaves a detached subtree executable — the attribute-form twin (hook-stripped subtree retains onload-class handlers). This report's rawtext **text** form is not covered by `_neutralizeSubtree`'s attribute stripping and is not that advisory.\n- GHSA-h8r8-wccr-v5f2 (medium): mXSS via re-contextualization in the standard (non-IN_PLACE) serialize path — different mechanism; IN_PLACE is not involved.\n- The 3.4.9 release notes credit @mozfreedyb for the IN_PLACE handling improvements that this residual escapes on the text axis.\n\n## Applicability scope (stated up front)\n\nThe payload materializes when the application **serializes and re-parses** the sanitizer output (`innerHTML` assignment, template rendering, markdown/HTML round trips) or otherwise consumes the returned node's markup. Moving the returned node via `appendChild` alone does not trigger it. Applications that pass **live, connected attacker trees** into `IN_PLACE` are explicitly warned against by upstream's own source comment; this report concerns the serialize-and-reinsert consumption pattern that the IN_PLACE mode exists to serve.",
  "severity" : [ ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "dompurify"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "3.4.16"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 3.4.15"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/cure53/DOMPurify/security/advisories/GHSA-6688-9rhm-gjv2"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/cure53/DOMPurify/pull/1636"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/cure53/DOMPurify/commit/b9b9d80f7e401771c2ccaef5f45def7eec8f27d7"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/cure53/DOMPurify"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/cure53/DOMPurify/releases/tag/3.4.16"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-79" ],
    "severity" : "LOW",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-10-05T23:43:53Z",
    "nvd_published_at" : null
  }
}