TinyMCE Cross-Site Scripting (XSS) vulnerability in handling external SVG files through Object or Embed elements

Impact

A cross-site scripting (XSS) vulnerability was discovered in TinyMCE’s content loading and content inserting code. A SVG image could be loaded though an object or embed element and that image could potentially contain a XSS payload.

Fix

TinyMCE 6.8.1 introduced a new convert_unsafe_embeds option to automatically convert object and embed elements respective of their type attribute. From TinyMCE 7.0.0 onwards, the convert_unsafe_embeds option is enabled by default.

Workarounds

If you are using TinyMCE 6.8.1 or higher, set convert_unsafe_embeds to true. For any earlier versions, a custom NodeFilter is recommended to remove or modify any object or embed elements. This can be added using the editor.parser.addNodeFilter and editor.serializer.addNodeFilter APIs.

Acknowledgements

Tiny Technologies would like to thank Toni Huttunen of Fraktal Oy for discovering this vulnerability.

References

• TinyMCE 6.8.1
• TinyMCE 7.0.0