CVE-2021-21391

Description

### Impact 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. ### Patches The problem has been recognized and patched. The fix will be available in version 27.0.0. ### For more information Email us at security@cksource.com if you have any questions or comments about this advisory. ### Acknowledgements The CKEditor 5 team would like to thank Yeting Li for recognizing and reporting these vulnerabilities.

How to fix CVE-2021-21391

To remediate CVE-2021-21391, upgrade the affected package to a fixed version below.

—upgrade to 27.0.0 or later
—upgrade to 27.0.0 or later
—upgrade to 27.0.0 or later
—upgrade to 27.0.0 or later
—upgrade to 27.0.0 or later
—upgrade to 27.0.0 or later
—upgrade to 27.0.0 or later
—upgrade to 27.0.0 or later

Is CVE-2021-21391 being exploited?

Low — EPSS is 1.4%, meaning exploitation activity has not been observed at scale.

Affected packages (8)

from 0, < 27.0.0
from 0, < 27.0.0
from 0, < 27.0.0
from 0, < 27.0.0
from 0, < 27.0.0
from 0, < 27.0.0
from 0, < 27.0.0
from 0, < 27.0.0

CVSS scores

Source	Version	Severity	Vector
osv	CVSS 3.1	MEDIUM6.5	CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H