CVE-2021-21391 Regular expression Denial of Service in multiple packages

What is CVE-2021-21391?

CVE-2021-21391 is a medium-severity vulnerability in ckeditor5, published on 29 Apr 2021.

Official description

CKEditor 5 provides a WYSIWYG editing solution. This CVE affects the following npm packages: ckeditor5-engine, ckeditor5-font, ckeditor5-image, ckeditor5-list, ckeditor5-markdown-gfm, ckeditor5-media-embed, ckeditor5-paste-from-office, and ckeditor5-widget. Following an internal audit, a regular expression denial of service (ReDoS) vulnerability has been discovered in multiple CKEditor 5 packages. The vulnerability allowed to abuse particular regular expressions, which could cause a significant performance drop resulting in a browser tab freeze. It affects all users using the CKEditor 5 packages listed above at version <= 26.0.0. The problem has been recognized and patched. The fix will be available in version 27.0.0.

Weakness: CWE-400

Which versions are affected by CVE-2021-21391?

16 open source packages ship an affected version, including @ckeditor/ckeditor5-engine, @ckeditor/ckeditor5-font and @ckeditor/ckeditor5-image. It affects 8 products.

Products include Ckeditor Ckeditor5-Engine, Ckeditor Ckeditor5-Font, Ckeditor Ckeditor5-Image, Ckeditor Ckeditor5-List, Ckeditor Ckeditor5-Markdown-Gfm, Ckeditor Ckeditor5-Media-Embed and 2 more.

How do I fix CVE-2021-21391?

Upgrade @ckeditor/ckeditor5-engine to 27.0.0 or later.

Is CVE-2021-21391 being exploited?

There is no known exploitation of CVE-2021-21391 in the wild and no public exploit code.

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as GHSA-3rh3-wfr4-76mj, UBUNTU-CVE-2021-21391.