Impact

Users can insert malicious code into file names when uploading files, which is then executed in tooltips and popups in the backend.

Patches

Update to Contao 4.13.40 or Contao 5.3.4.

Workarounds

Disable uploads for untrusted users.

References

https://contao.org/en/security-advisories/cross-site-scripting-in-the-file-manager

For more information

If you have any questions or comments about this advisory, open an issue in contao/contao.

Credits

Thanks to Alexander Wuttke for reporting this vulnerability.