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Vulnerability record · CVE-2021-21254 · published 29 January 2021

CVE-2021-21254: Ckeditor5 uncontrolled resource consumption vulnerability

Ckeditor · Ckeditor5

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.

6.5 CVSS 3.1 Medium EPSS 1.8% · top 22.4% CWE-400 · Uncontrolled resource consumption
6.5CVSS 3.1 base score, v2 4.0
1.8%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
6References
17 Jun 2026Last modified by NVD

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.

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

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://github.com/ckeditor/ckeditor5/releases/tag/v25.0.0 Release NotesThird Party Advisory
https://github.com/ckeditor/ckeditor5/security/advisories/GHSA-hgmg-hhc8-g5wr Third Party Advisory
https://www.npmjs.com/package/%40ckeditor/ckeditor5-markdown-gfm
https://github.com/ckeditor/ckeditor5/releases/tag/v25.0.0 Release NotesThird Party Advisory
https://github.com/ckeditor/ckeditor5/security/advisories/GHSA-hgmg-hhc8-g5wr Third Party Advisory
https://www.npmjs.com/package/%40ckeditor/ckeditor5-markdown-gfm

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Same products first, then exploited flaws of the same weakness class.

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Source: NIST National Vulnerability Database (record CVE-2021-21254), CISA KEV, FIRST EPSS (scores of 2026-09-30). This page is refreshed as NVD updates the record.