Craft CMS has potential authenticated Remote Code Execution via Twig SSTI

For this to work, the attacker must have administrator access to the Craft Control Panel, and allowAdminChanges must be enabled, which is against Craft CMS' recommendations for any non-dev environment.

https://craftcms.com/knowledge-base/securing-craft#set-allowAdminChanges-to-false-in-production

Alternatively, they can have a non-administrator account with allowAdminChanges disabled, but they must have access to the System Messages utility.

It is possible to craft a malicious payload using the Twig map filter in text fields that accept Twig input under Settings in the Craft control panel or using the System Messages utility, which could lead to a RCE.

Users should update to the patched versions (5.8.22 and 4.16.18) to mitigate the issue.

References:

https://github.com/craftcms/cms/pull/18208