VulnerabilityModified

CVE-2021-21391

Following an internal audit, a regular expression denial of service (ReDoS) vulnerability has been discovered in multiple CKEditor 5 packages.

MEDIUM 6.5EPSS 1.67%

Does this matter?

Lower severity and a low EPSS score (1.67%). Track it; it rarely justifies an emergency change on its own.

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.

CVSS 3.1: 6.5 MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
EPSS: 1.67% probability · 77th percentile
Public exploits: None in Exploit-DB
CISA KEV: Not listed
Weakness: CWE-400
Affected: ckeditor/ckeditor5-engine · ckeditor/ckeditor5-font · ckeditor/ckeditor5-image · ckeditor/ckeditor5-list · ckeditor/ckeditor5-markdown-gfm · ckeditor/ckeditor5-media-embed · ckeditor/ckeditor5-paste-from-office · ckeditor/ckeditor5-widget
Source: security-advisories@github.com

EPSS trend

EPSS 1.7% since 26 October 2026; no change recorded yet. Points are recorded when the score first appears and whenever it moves by a percentage point or more.

References

Source: NVD record, EPSS from FIRST.org, KEV from CISA, exploits from Exploit-DB. Refreshed daily. Download this record as JSON.