CVE-2023-45818

TinyMCE mXSS vulnerability in undo/redo, getContent API, resetContent API, and Autosave plugin

Fix

To avoid this vulnerability:

• Upgrade to TinyMCE 5.10.8 or higher for TinyMCE 5.x.
• Upgrade to TinyMCE 6.7.1 or higher for TinyMCE 6.x.

Acknowledgements

Tiny Technologies would like to thank Masato Kinugawa of Cure53 for discovering this vulnerability.

References

• TinyMCE 5.10.8 Release Notes
• TinyMCE 6.7.1 Release Notes

For more information

If you have any questions or comments about this advisory:

• Email us at [email protected]
• Open an issue in the TinyMCE repo

A mutation cross-site scripting (mXSS) vulnerability was discovered in TinyMCE’s core undo and redo functionality. When a carefully-crafted HTML snippet passes the XSS sanitisation layer, it is manipulated as a string by internal trimming functions before being stored in the undo stack. If the HTML snippet is restored from the undo stack, the combination of the string manipulation and reparative parsing by either the browser's native DOMParser API (TinyMCE 6) or the SaxParser API (TinyMCE 5) mutates the HTML maliciously, allowing an XSS payload to be executed.
​This vulnerability also impacts these related TinyMCE APIs and plugins:​

• tinymce.Editor.getContent({ format: 'raw' })
• tinymce.Editor.resetContent()
• Autosave Plugin

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-2023-45818 has a CVSS score of 6.1 (Medium). The vector is network-reachable, no privileges required, and user interaction required. 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 (6.7.1, 5.10.8); upgrading removes the vulnerable code path.

Kodem intelligence

Already deployed Kodem?

This vulnerability has been patched in TinyMCE 5.10.8 and TinyMCE 6.7.1 by ensuring HTML is trimmed using node-level manipulation instead of string manipulation.

1. What is CVE-2023-45818? CVE-2023-45818 is a medium-severity cross-site scripting (XSS) vulnerability in tinymce (npm), affecting versions >= 6.0.0, < 6.7.1. It is fixed in 6.7.1, 5.10.8. Untrusted input is rendered as active markup in a victim's browser, which can run script in their session.
2. How severe is CVE-2023-45818? CVE-2023-45818 has a CVSS score of 6.1 (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-2023-45818?
   • tinymce (npm) (versions >= 6.0.0, < 6.7.1)
   • TinyMCE (nuget) (versions >= 6.0.0, < 6.7.1)
   • tinymce/tinymce (composer) (versions >= 6.0.0, < 6.7.1)
4. Is there a fix for CVE-2023-45818? Yes. CVE-2023-45818 is fixed in 6.7.1, 5.10.8. Upgrade to this version or later.
5. Is CVE-2023-45818 exploitable, and should I be worried? Whether CVE-2023-45818 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-2023-45818 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-2023-45818?
   • Upgrade tinymce to 6.7.1 or later
   • Upgrade TinyMCE to 6.7.1 or later
   • Upgrade tinymce/tinymce to 6.7.1 or later
   • Upgrade tinymce to 5.10.8 or later
   • Upgrade TinyMCE to 5.10.8 or later
   • Upgrade tinymce/tinymce to 5.10.8 or later

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