https://www.qualys.com/2022/01/25/cve-2021-4034/pwnkit.txt
" "Polkit (formerly PolicyKit) is a component for controlling system-wide privileges in Unix-like operating systems. It provides an organized way for non-privileged processes to communicate with privileged ones. [...] It is also possible to use polkit to execute commands with elevated privileges using the command pkexec followed by the command intended to be executed (with root permission)." (Wikipedia)
This vulnerability is an attacker's dream come true:
-
pkexec is installed by default on all major Linux distributions (we exploited Ubuntu, Debian, Fedora, CentOS, and other distributions are probably also exploitable);
-
pkexec is vulnerable since its creation, in May 2009 (commit c8c3d83, "Add a pkexec(1) command");
-
any unprivileged local user can exploit this vulnerability to obtain full root privileges;
-
although this vulnerability is technically a memory corruption, it is exploitable instantly, reliably, in an architecture-independent way;
-
and it is exploitable even if the polkit daemon itself is not running.
We will not publish our exploit immediately; however, please note that this vulnerability is trivially exploitable, and other researchers might publish their exploits shortly after the patches are available. If no patches are available for your operating system, you can remove the SUID-bit from pkexec as a temporary mitigation; for example:
This vulnerability is one of our most beautiful discoveries; to honor its memory, we recommend listening to DJ Pone's "Falken's Maze" (double pun intended) while reading this advisory. Thank you very much! "