In guix-daemon in GNU Guix before 1618ca7, a content-addressed-mirrors file can be written to create a setuid program that allows a regular user to gain the privileges of the build user that runs it (even after the build has ended).
https://guix.gnu.org/en/blog/2025/privilege-escalation-vulnerability-2025-2/
https://codeberg.org/guix/guix/commit/1618ca7aa2ee8b6519ee9fd0b965e15eca2bfe45