DOMPurify: Trusted Types policy survives clearConfig() and can poison later RETURN_TRUSTED_TYPE output

Exploitation

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

CVSS 4.0

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

EPSS

• CVE-2026-65899: 0.41% estimated exploitation activity in the next 30 days; percentile 35.59 (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.

Impact A DOMPurify instance that is reused across trust boundaries can stay bound to a previously supplied TRUSTEDTYPESPOLICY even after clearConfig() is called. A later caller that requests RETURNTRUSTEDTYPE receives a TrustedHTML object created by the old policy, not by a clean default configuration. If the old policy is unsafe or controlled by a less-trusted integration, this turns a later "default" sanitize call into script execution at a Trusted Types sink. TRUSTEDTYPESPOLICY: null on the later call also does not clear the retained policy. dompurify-trusted-types-policy-survives-clearconfig-poc.js Affected version Tested against DOMPurify 3.4.8, repository commit 825e617753ac1169306a542d3174a77f717a0cf6. Root cause parseConfig() overwrites trustedTypesPolicy when cfg.TRUSTEDTYPESPOLICY is truthy, but the default/null path only initializes the internal policy when trustedTypesPolicy === undefined. Once a custom policy has been set, later default config parsing leaves it in place.…

Published by the source

15 Jun 2026, 20:12 UTC

Last modified by the source

10 Sep 2026, 03:50 UTC

Source last checked

26 Oct 2026, 12:58 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-vxr8-fq34-vvx9

2. Revision 2 · amended · 25 Oct 2026

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

3. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-vxr8-fq34-vvx9

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# Patch Next advisory brief: CVE-2026-65899

Advisory: DOMPurify: Trusted Types policy survives `clearConfig()` and can poison later `RETURN_TRUSTED_TYPE` output
IDs: CVE-2026-65899, GHSA-vxr8-fq34-vvx9
Record: https://patchnext.com/advisories/cve-2026-65899 (revision 3, source checked 26 Oct 2026, 12:58 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Low (CVSS 2.1)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: dompurify 3.4.9. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm dompurify: affected < 3.4.9; fixed in 3.4.9

## 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://osv.dev/vulnerability/GHSA-vxr8-fq34-vvx9 (OSV record GHSA-vxr8-fq34-vvx9 lists affected ranges: npm dompurify >=0 <3.4.9 (fixed))
- Verified: https://github.com/advisories/GHSA-vxr8-fq34-vvx9 (GitHub-reviewed advisory GHSA-vxr8-fq34-vvx9 lists affected ranges: npm dompurify >=0 <3.4.9)

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