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CKEditor 5 Markdown plugin Regular expression Denial of Service

Moderate severity GitHub Reviewed Published Jan 28, 2021 in ckeditor/ckeditor5 • Updated Jan 30, 2023

Package

npm @ckeditor/ckeditor5-markdown-gfm (npm)

Affected versions

<= 24.0.0

Patched versions

25.0.0

Description

Impact

A regular expression denial of service (ReDoS) vulnerability has been discovered in the CKEditor 5 Markdown plugin code. The vulnerability allowed to abuse a link recognition regular expression, which could cause a significant performance drop resulting in a browser tab freeze. It affects all users using the CKEditor 5 Markdown plugin at version <= 24.0.0.

Patches

The problem has been recognized and patched. The fix will be available in version 25.0.0.

Workarounds

The user can work around the issue by:

  • Upgrading CKEditor 5 to version 25.0.0.
  • Disabling the Markdown plugin.

More information

If you have any questions or comments about this advisory:

Acknowledgements

The CKEditor 5 team would like to thank Erik Krogh Kristensen from the GitHub team for recognizing this vulnerability and
Alvaro Muñoz from GitHub for reporting it.

References

@Mgsy Mgsy published to ckeditor/ckeditor5 Jan 28, 2021
Reviewed Jan 29, 2021
Published to the GitHub Advisory Database Jan 29, 2021
Published by the National Vulnerability Database Jan 29, 2021
Last updated Jan 30, 2023

Severity

Moderate

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
Low
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

EPSS score

0.097%
(42nd percentile)

Weaknesses

CVE ID

CVE-2021-21254

GHSA ID

GHSA-hgmg-hhc8-g5wr

Source code

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