Ubuntu Security Notice 6453-1 - Jan-Niklas Sohn discovered that the X.Org X Server incorrectly handled prepending values to certain properties. An attacker could possibly use this issue to cause the X Server to crash, execute arbitrary code, or escalate privileges. Sri discovered that the X.Org X Server incorrectly handled destroying windows in certain legacy multi-screen setups. An attacker could possibly use this issue to cause the X Server to crash, execute arbitrary code, or escalate privileges.