pkexec from the PolKit (Policy Kit) program can be used to gain root privileges (CVE-2021-4034) on most modern Linux distributions.
The memory corruption bug in pkexec allows programs to be executed using elevated privileges. The pkexec command allows for non-privileged accounts to execute commands using elevated privileges.
Qualys security researchers have been able to independently verify the vulnerability, develop an exploit, and obtain full root privileges on default installations of Ubuntu, Debian, Fedora, and CentOS. Other Linux distributions are likely vulnerable and probably exploitable.