Impact

A cross-site scripting (XSS) vulnerability was discovered in the schema validation logic of the core parser. The vulnerability allowed arbitrary JavaScript execution when inserting a specially crafted piece of content into the editor using the clipboard or editor APIs. This malicious content could then end up in content published outside the editor, if no server-side sanitization was performed. This impacts all users who are using TinyMCE 5.8.2 or lower.

Patches

This vulnerability has been patched in TinyMCE 5.9.0 by ensuring schema validation was still performed after unwrapping invalid elements.

Workarounds

To work around this vulnerability, either:

• Upgrade to TinyMCE 5.9.0 or higher
• Manually sanitize the content using the BeforeSetContent event (see below)

Example: Manually sanitize content

editor.on('BeforeSetContent', function(e) {
  var sanitizedContent = ...; // Manually sanitize content here
  e.content = sanitizedContent;
});

Acknowledgements

Tiny Technologies would like to thank William Bowling for discovering this vulnerability.

References

https://www.tiny.cloud/docs/release-notes/release-notes59/#securityfixes

For more information

If you have any questions or comments about this advisory:

• Email us at infosec@tiny.cloud
• Open an issue in the TinyMCE repo

References

• GHSA-5h9g-x5rv-25wg
• https://www.tiny.cloud/docs/release-notes/release-notes59/#securityfixes