Ubuntu Security Notice 3453-1 - Michal Srb discovered that the X.Org X server incorrectly handled shared memory segments. An attacker able to connect to an X server, either locally or remotely, could use this issue to crash the server, or possibly replace shared memory segments of other X clients in the same session. Michal Srb discovered that the X.Org X server incorrectly handled XKB buffers. An attacker able to connect to an X server, either locally or remotely, could use this issue to crash the server, or possibly execute arbitrary code. Various other issues were also addressed.
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