XSS in TinyMCE

Impact

A cross-site scripting (XSS) vulnerability was discovered in: the core parser and media plugin. The vulnerability allowed arbitrary JavaScript execution when inserting a specially crafted piece of content into the editor via the clipboard or APIs. This impacts all users who are using TinyMCE 4.9.9 or lower and TinyMCE 5.2.1 or lower.

Patches

This vulnerability has been patched in TinyMCE 4.9.10 and 5.2.2 by improved HTML parsing and sanitization logic.

Workarounds

The workarounds available are:

• disable the media plugin and manually sanitize CDATA content (see below)

or

• upgrade to either TinyMCE 4.9.10 or TinyMCE 5.2.2

Example: Manually strip CDATA elements

setup: function(editor) {
  editor.on('PreInit', function() {
    editor.parser.addNodeFilter('#cdata', function(nodes) {
      for (var i = 0; i < nodes.length; i++) {
        nodes[i].remove();
      }
    });
  });
}

Acknowledgements

Tiny Technologies would like to thank Michał Bentkowski and intivesec for discovering these vulnerabilities.

References

https://www.tiny.cloud/docs/release-notes/release-notes522/#securityfixes

For more information

If you have any questions or comments about this advisory:

• Open an issue in the TinyMCE repo
• Email us at [infosec@tiny.cloud](mailto:infosec@tiny.cloud)