Impact

It is possible to inject code into the tl_log table that will be executed in the browser when the system log is called in the back end.

Patches

Update to Contao 4.9.16 or 4.11.5.

Workarounds

Disable the system log module in the back end for all users (especially admin users).

References

https://contao.org/en/security-advisories/cross-site-scripting-in-the-system-log-2021

For more information

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

References

• GHSA-h58v-c6rf-g9f7
• https://nvd.nist.gov/vuln/detail/CVE-2021-35210
• https://contao.org/en/security-advisories/cross-site-scripting-in-the-system-log-2021.html
• https://github.com/FriendsOfPHP/security-advisories/blob/master/contao/contao/CVE-2021-35210.yaml
• https://github.com/FriendsOfPHP/security-advisories/blob/master/contao/core-bundle/CVE-2021-35210.yaml