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CKEditor 5 has Cross-site Scripting (XSS) in the HTML Support package

Moderate severity GitHub Reviewed Published Mar 4, 2026 in ckeditor/ckeditor5 • Updated Mar 19, 2026

Package

npm @ckeditor/ckeditor5-html-support (npm)

Affected versions

>= 29.0.0, < 47.6.0

Patched versions

47.6.0
npm ckeditor5 (npm)
>= 29.0.0, < 47.6.0
47.6.0

Description

Impact

A Cross-Site Scripting (XSS) vulnerability has been discovered in the General HTML Support feature. This vulnerability could be triggered by inserting specially crafted markup, leading to unauthorized JavaScript code execution, if the editor instance used an unsafe General HTML Support configuration.

This vulnerability affects only installations where the editor configuration meets the following criteria:

Patches

The problem has been recognized and patched. The fix will be available in version 47.6.0 (and above).

Workarounds

CKEditor 5 recommends configuring General HTML Support securely to ensure that unsafe content is not accepted. Please refer to the Security section for detailed guidance.

Credits

CKEditor 5 would like to thank:

  • Emilio Kevin
  • Jeongwoo Lee, Younsoung Kim, Minseok Kim and Jinyeong Kim from ENKI Whitehat

for responsibly reporting this vulnerability.

For more information

Email us at security@cksource.com if you have any questions or comments about this advisory.

References

@Mgsy Mgsy published to ckeditor/ckeditor5 Mar 4, 2026
Published to the GitHub Advisory Database Mar 4, 2026
Reviewed Mar 4, 2026
Published by the National Vulnerability Database Mar 5, 2026
Last updated Mar 19, 2026

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
Changed
Confidentiality
Low
Integrity
Low
Availability
None

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:C/C:L/I:L/A:N

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(11th percentile)

Weaknesses

Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users. Learn more on MITRE.

CVE ID

CVE-2026-28343

GHSA ID

GHSA-jrqm-vmqc-gm93

Source code

Credits

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