DOMPurify XSS via `selectedcontent` re-clone

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

DOMPurify is a DOM-only cross-site scripting sanitizer for HTML, MathML, and SVG. In 3.4.4, DOMPurify allowed selectedcontent by default, allowing browsers to re-clone an XSS payload after sanitization so that unsanitized markup inside <selectedcontent> is returned. This issue is fixed in version 3.4.5.

Source published

14 Jul 2026 19:56:02 UTC

Source modified

16 Jul 2026 14:47:21 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: cve-program · CVE Program Terms of Use. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 3.1 · 8.2 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:L/A:N

DOMPurify is a DOM-only cross-site scripting sanitizer for HTML, MathML, and SVG. In 3.4.4, DOMPurify allowed selectedcontent by default, allowing browsers to re-clone an XSS payload after sanitization so that unsanitized markup inside <selectedcontent> is returned. This issue is fixed in version 3.4.5.

Source published

14 Jul 2026 20:17:02 UTC

Source modified

24 Oct 2026 21:10:00 UTC

Observed here

25 Oct 2026 12:17:26 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 3.1 · [email protected] · Secondary · 8.2 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:L/A:N

### 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: 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 ```js 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: ```html <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: ```html <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](https://developer.mozilla.org/en-US/docs/Web/HTML/Reference/Elements/selectedcontent) 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.

Source published

1 Jun 2026 14:07:29 UTC

Source modified

1 Jun 2026 14:26:26 UTC

Observed here

24 Oct 2026 13:17:17 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:L/A:N

Publisher rating · HIGH