Impact

Authenticated users can inject malicious code in widgets with units, which is then executed both in the element preview (back end) and on the website (front end).

Patches

Update to Contao 4.9.42, 4.13.28 or 5.1.10.

Workarounds

Disable login for all untrusted back end users.

References

https://contao.org/en/security-advisories/cross-site-scripting-in-widgets-with-units

For more information

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

Credits

Thanks to Christian Pöschl and Fabian Brenner from usd AG for reporting this vulnerability.