CVE-2026-28343

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 [email protected] if you have any questions or comments about this advisory.

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:

• General HTML Support is enabled,
• General HTML Support configuration allows inserting unsafe markup (see Security section to learn more).

Untrusted input is rendered as active markup in a victim's browser, which can run script in their session. Typical impact: session or credential theft, and actions taken as the user.

CVE-2026-28343 has a CVSS score of 6.4 (Medium). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (47.6.0); upgrading removes the vulnerable code path.

Kodem intelligence

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

1. What is CVE-2026-28343? CVE-2026-28343 is a medium-severity cross-site scripting (XSS) vulnerability in @ckeditor/ckeditor5-html-support (npm), affecting versions >= 29.0.0, < 47.6.0. It is fixed in 47.6.0. Untrusted input is rendered as active markup in a victim's browser, which can run script in their session.
2. How severe is CVE-2026-28343? CVE-2026-28343 has a CVSS score of 6.4 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which packages are affected by CVE-2026-28343?
   • @ckeditor/ckeditor5-html-support (npm) (versions >= 29.0.0, < 47.6.0)
   • ckeditor5 (npm) (versions >= 29.0.0, < 47.6.0)
4. Is there a fix for CVE-2026-28343? Yes. CVE-2026-28343 is fixed in 47.6.0. Upgrade to this version or later.
5. Is CVE-2026-28343 exploitable, and should I be worried? Whether CVE-2026-28343 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-28343 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-28343?
   • Upgrade @ckeditor/ckeditor5-html-support to 47.6.0 or later
   • Upgrade ckeditor5 to 47.6.0 or later