Ubuntu Security Notice USN-6555-2

Ubuntu Security Notice 6555-2 - USN-6555-1 fixed several vulnerabilities in X.Org. This update provides the corresponding update for Ubuntu 16.04 LTS and Ubuntu 18.04 LTS. Jan-Niklas Sohn discovered that the X.Org X Server incorrectly handled XKB button actions. An attacker could possibly use this issue to cause the X Server to crash, execute arbitrary code, or escalate privileges.