Ubuntu Security Notice 6168-2 - USN-6168-1 fixed a vulnerability in libx11. This update provides the corresponding update for Ubuntu 14.04 ESM, Ubuntu 16.04 ESM, and Ubuntu 18.04 ESM. Gregory James Duck discovered that libx11 incorrectly handled certain Request, Event, or Error IDs. If a user were tricked into connecting to a malicious X Server, a remote attacker could possibly use this issue to cause libx11 to crash, resulting in a denial of service.
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