Privilege Escalation

bullseye is vulnerable to privilege escalation.The attack consists in having an unprivileged user spawn a build process, for instance with guix build, that makes its build directory world-writable. The user then creates a hardlink to a root-owned file such as /etc/shadow in that build directory. If the user passed the --keep-failed option and the build eventually fails, the daemon changes ownership of the whole build tree,including the hardlink, to the user. At that point, the user has write access to the target file.