CVE-2021-21254

Name: CVE-2021-21254
Creator: NVD / NIST
Published: 2021-01-29T22:15:14.797+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

MEDIUMCVSS 6.5/10EPSS 1.79%

Last modified Jun 17, 2026

CVE-2021-21254 is a medium-severity vulnerability rated 6.5/10 on the CVSS scale. CKEditor 5 is an open source rich text editor framework with a modular architecture. The CKEditor 5 Markdown plugin (@ckeditor/ckeditor5-markdown-gfm) before version 25.0.0 has a regex denial of service (ReDoS) vulnerability. EPSS estimates a 1.79% chance of exploitation in the next 30 days.

Description

CKEditor 5 is an open source rich text editor framework with a modular architecture. The CKEditor 5 Markdown plugin (@ckeditor/ckeditor5-markdown-gfm) before version 25.0.0 has a regex denial of service (ReDoS) vulnerability. The vulnerability allowed to abuse link recognition regular expression, which could cause a significant performance drop resulting in browser tab freeze. It affects all users using CKEditor 5 Markdown plugin at version <= 24.0.0. The problem has been recognized and patched. The fix will be available in version 25.0.0.

Metrics

CVSS 3.1

6.5/10

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

EPSS Probability

1.79%

75.6th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-400

Affected Software

Vendor	Product	Versions
Ckeditor	Ckeditor5	< 25.0.0

References

https://github.com/ckeditor/ckeditor5/releases/tag/v25.0.0Release Notes, Third Party Advisory
https://github.com/ckeditor/ckeditor5/security/advisories/GHSA-hgmg-hhc8-g5wrThird Party Advisory
https://www.npmjs.com/package/%40ckeditor/ckeditor5-markdown-gfm
https://github.com/ckeditor/ckeditor5/releases/tag/v25.0.0Release Notes, Third Party Advisory
https://github.com/ckeditor/ckeditor5/security/advisories/GHSA-hgmg-hhc8-g5wrThird Party Advisory
https://www.npmjs.com/package/%40ckeditor/ckeditor5-markdown-gfm

Timeline

Published: Jan 29, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-21254?

How severe is CVE-2021-21254?

CVE-2021-21254 has a CVSS score of 6.5/10 (MEDIUM severity). The EPSS model estimates a 1.79% probability of exploitation in the next 30 days.

How do I fix CVE-2021-21254?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-21254?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST