systemd-tmpfiles could be made to change ownership of arbitrary files.
USN-3816-1 fixed several vulnerabilities in systemd. However, the fix for CVE-2018-6954 was not sufficient. This update provides the remaining fixes.
19 November 2018
A security issue affects these releases of Ubuntu and its derivatives:
systemd-tmpfiles could be made to change ownership of arbitrary files.
USN-3816-1 fixed several vulnerabilities in systemd. However, the fix for CVE-2018-6954 was not sufficient. This update provides the remaining fixes.
We apologize for the inconvenience.
Original advisory details:
Jann Horn discovered that unit_deserialize incorrectly handled status messages above a certain length. A local attacker could potentially exploit this via NotifyAccess to inject arbitrary state across re-execution and obtain root privileges. (CVE-2018-15686)
Jann Horn discovered a race condition in chown_one(). A local attacker could potentially exploit this by setting arbitrary permissions on certain files to obtain root privileges. This issue only affected Ubuntu 18.04 LTS and Ubuntu 18.10. (CVE-2018-15687)
It was discovered that systemd-tmpfiles mishandled symlinks in non-terminal path components. A local attacker could potentially exploit this by gaining ownership of certain files to obtain root privileges. This issue only affected Ubuntu 16.04 LTS and Ubuntu 18.04 LTS. (CVE-2018-6954)
The problem can be corrected by updating your system to the following package versions:
To update your system, please follow these instructions: https://wiki.ubuntu.com/Security/Upgrades.
After a standard system update you need to reboot your computer to make all the necessary changes.
Vulmon