Pwnkit is installed by default in most linux distributions, there is no permanent fix yet but there is a workaround, you can remove the suid bit from the binary using chmod 0755 /usr/bin/pkexec and that will make it impossible to exploit this bug.
- Pkexec is installed by default on all major Linux distributions.
- Pkexec has been vulnerable since its creation in May 2009.
- Any unprivileged local user can exploit this vulnerability to get full root privileges.
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-4034