HTML comments vulnerability allowing to execute JavaScript code

Exploitation

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

CVSS

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

EPSS

• CVE-2021-41165: 1.57% estimated exploitation activity in the next 30 days; percentile 75.45 (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.

Affected packages The vulnerability has been discovered in the core HTML processing module and may affect all plugins used by CKEditor 4. Impact A potential vulnerability has been discovered in CKEditor 4 HTML processing core module. The vulnerability allowed to inject malformed comments HTML bypassing content sanitization, which could result in executing JavaScript code. It affects all users using the CKEditor 4 at version < 4.17.0. Patches The problem has been recognized and patched. The fix will be available in version 4.17.0. For more information Email us at security@cksource.com if you have any questions or comments about this advisory. Acknowledgements The CKEditor 4 team would like to thank William Bowling (wbowling) for recognizing and reporting this vulnerability.

Published by the source

17 Nov 2021, 21:58 UTC

Last modified by the source

8 Jul 2026, 06:28 UTC

Source last checked

26 Oct 2026, 12:30 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-7h26-63m7-qhf2

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-7h26-63m7-qhf2

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2021-41165

Advisory: HTML comments vulnerability allowing to execute JavaScript code
IDs: CVE-2021-41165, GHSA-7h26-63m7-qhf2
Record: https://patchnext.com/advisories/cve-2021-41165 (revision 2, source checked 26 Oct 2026, 12:30 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.2)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: ckeditor4 4.17.0; ckeditor/ckeditor 4.17.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm ckeditor4: affected < 4.17.0; fixed in 4.17.0
- Packagist ckeditor/ckeditor: affected < 4.17.0; fixed in 4.17.0

## Suggested inspection (read-only)
- `npm ls ckeditor4 --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.
- Packagist ckeditor/ckeditor: check the installed version with your package manager.

## 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 ckeditor4, ckeditor/ckeditor.
- 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-7h26-63m7-qhf2 (OSV record GHSA-7h26-63m7-qhf2 lists affected ranges: npm ckeditor4 >=0 =0 <4.17.0 (fixed))
- Verified: https://github.com/advisories/GHSA-7h26-63m7-qhf2 (GitHub-reviewed advisory GHSA-7h26-63m7-qhf2 lists affected ranges: npm ckeditor4 >=0 =0 <4.17.0)

Commands are suggestions: review each one before running it.