CKEditor 5 Markdown plugin Regular expression Denial of Service

Impact

A regular expression denial of service (ReDoS) vulnerability has been discovered in the CKEditor 5 Markdown plugin code. The vulnerability allowed to abuse a link recognition regular expression, which could cause a significant performance drop resulting in a browser tab freeze. It affects all users using the CKEditor 5 Markdown plugin at version <= 24.0.0.

Patches

The problem has been recognized and patched. The fix will be available in version 25.0.0.

Workarounds

The user can work around the issue by:

• Upgrading CKEditor 5 to version 25.0.0.
• Disabling the Markdown plugin.

More information

If you have any questions or comments about this advisory:

• Email us at [email protected]

Acknowledgements

The CKEditor 5 team would like to thank Erik Krogh Kristensen from the GitHub team for recognizing this vulnerability and
Alvaro Muñoz from GitHub for reporting it.