DOMPurify SAFE_FOR_TEMPLATES bypass: split template expressions survive in attached shadow root content on DOM output modes

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

9.2 · CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:H/VA:L/SC:N/SI:N/SA:N · score source

EPSS

• CVE-2026-116804: 0.18% estimated exploitation activity in the next 30 days; percentile 7.45 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary When DOMPurify is configured with `SAFE_FOR_TEMPLATES: true` together with a DOM-returning mode (`RETURN_DOM: true`, `RETURN_DOM_FRAGMENT: true`, or `IN_PLACE: true`), template expressions such as `{{...}}`, `${...}`, and ` ` survive sanitization inside the text content of an attached shadow root. The post-walk safety net `_scrubTemplateExpressions` (`src/purify.ts:1717`) was extended to recurse into ` .content`, but it never recurses into attached shadow roots. An attacker who can supply a DOM node carrying a shadow root (the `IN_PLACE` and shadow-aware `RETURN_DOM` surfaces) can split an expression across text nodes separated by disallowed elements; after those elements are removed the fragments become adjacent and serialize into a complete expression that a downstream template engine will evaluate.

Root Cause `SAFE_FOR_TEMPLATES` neutralizes template expressions through two mechanisms: a per-text-node strip during the main walk (`_stripTemplateExpressions`, applied…

Published by the source

22 Oct 2026, 16:25 UTC

Last modified by the source

27 Oct 2026, 10:56 UTC

Source last checked

28 Oct 2026, 06:00 UTC

1. Revision 6 · amended · 28 Oct 2026

   Amended from osv record GHSA-cg2g-xh64-v4q7

2. Revision 5 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-cg2g-xh64-v4q7

3. Revision 4 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-cg2g-xh64-v4q7

4. Revision 3 · amended · 24 Oct 2026

   Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

5. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GHSA-cg2g-xh64-v4q7

6. Revision 1 · created · 23 Oct 2026

   Published from ghsa record GHSA-cg2g-xh64-v4q7

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# Patch Next advisory brief: CVE-2026-116804

Advisory: DOMPurify SAFE_FOR_TEMPLATES bypass: split template expressions survive in attached shadow root content on DOM output modes
IDs: CVE-2026-116804, GHSA-cg2g-xh64-v4q7
Record: https://patchnext.com/advisories/ghsa-cg2g-xh64-v4q7 (revision 6, source checked 28 Oct 2026, 06:00 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Critical (CVSS 9.2)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: dompurify 3.4.17. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm dompurify: affected >= 3.4.4, < 3.4.17; fixed in 3.4.17

## Suggested inspection (read-only)
- `npm ls dompurify --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on dompurify.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-cg2g-xh64-v4q7 (GitHub-reviewed advisory GHSA-cg2g-xh64-v4q7 lists affected ranges: npm dompurify >=3.4.4 <=3.4.16)
- Verified: https://osv.dev/vulnerability/GHSA-cg2g-xh64-v4q7 (OSV record GHSA-cg2g-xh64-v4q7 lists affected ranges: npm dompurify >=3.4.4 <3.4.17 (fixed))

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