It’s a privilege escalation vulnerability:
Linux users on Tuesday got a major dose of bad news — a 12-year-old vulnerability in a system tool called Polkit gives attackers unfettered root privileges on machines running most major distributions of the open source operating system.
Previously called PolicyKit, Polkit manages system-wide privileges in Unix-like OSes. It provides a mechanism for nonprivileged processes to safely interact with privileged processes. It also allows users to execute commands with high privileges by using a component called pkexec, followed by the command.
It was discovered in October, and disclosed last week — after most Linux distributions issued patches. Of course, there’s lots of Linux out there that never gets patched, so expect this to be exploited in the wild for a long time.
Of course, this vulnerability doesn’t give attackers access to the system. They have to get that some other way. But if they get access, this vulnerability gives them root privileges.