Key excerpt/context from the advisory:
We discovered a Local Privilege Escalation (from any user to root) in
polkit's pkexec, a SUID-root program that is installed by default on
every major Linux distribution:
"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.
