CVE-2026-28343: CKEditor 5 cross-site scripting in HTML Support

CVE-2026-28343 · Severity: low · CVSS 3.1 · Published 2026-03-04

CKEditor 5 is a popular rich-text editor used on many websites to allow users to create and format content. A cross-site scripting (XSS) vulnerability in its HTML Support feature could allow attackers to inject malicious JavaScript code that executes in the context of a website, potentially stealing user credentials or session data if the editor is misconfigured to accept unsafe HTML markup.

Technologies: CKEditor 5, ckeditor5 (npm). Vendors: CKEditor, npm.

Quick answers

Is CVE-2026-28343 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-28343 being exploited in the wild.
How severe is CVE-2026-28343?
Low severity, with a CVSS score of 3.1, published 4 March 2026.
Which products and versions are affected?
CKEditor 5 29.0.0 to 47.5.x; Ckeditor5-Html-Support 29.0.0 to 47.5.x; @ckeditor/ckeditor5-html-support (npm) SEMVER:introduced=29.0.0,fixed=47.6.0; ckeditor5 (npm) SEMVER:introduced=29.0.0,fixed=47.6.0.
Is there a fix for CVE-2026-28343?
Yes. @ckeditor/ckeditor5-html-support (npm): upgrade to 47.6.0 or later; ckeditor5 (npm): upgrade to 47.6.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-28343 attacked?
It is attacked over the network, in a software library.
Am I affected by CVE-2026-28343?
Check whether you run CKEditor 5, Ckeditor5-Html-Support, @ckeditor/ckeditor5-html-support (npm) or one of the others listed at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

  • @ckeditor/ckeditor5-html-support (npm): upgrade to 47.6.0 or later
    npm install @ckeditor/ckeditor5-html-support@47.6.0
  • ckeditor5 (npm): upgrade to 47.6.0 or later
    npm install ckeditor5@47.6.0

Technical details

A Cross-Site Scripting (XSS) vulnerability exists in the General HTML Support feature of CKEditor 5 (CWE-79). The vulnerability can be triggered when an attacker inserts specially crafted markup into an editor instance that has General HTML Support enabled with an unsafe configuration allowing unsafe markup insertion. The attack requires low privilege level and does not require user interaction, but only affects installations where General HTML Support is explicitly enabled and misconfigured. Attackers can execute arbitrary JavaScript code in the context of the affected website. The vulnerability was patched in version 47.6.0 and above; users should upgrade immediately or implement secure General HTML Support configuration as recommended in the advisory.

Affected products

  • CKEditor CKEditor 5 29.0.0 to 47.5.x
  • CKEditor ckeditor5-html-support 29.0.0 to 47.5.x

Identifiers

  • CVE-2026-28343
  • GHSA-jrqm-vmqc-gm93

Timeline

  • 2026-03-04: disclosed: Vulnerability published via GHSA-jrqm-vmqc-gm93
  • 2026-03-04: patched: Fix available in version 47.6.0 and above

References

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