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Ubuntu Security Notice USN-6555-2
December 13, 2023

xorg-server vulnerabilities
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A security issue affects these releases of Ubuntu and its derivatives:

- Ubuntu 18.04 LTS (Available with Ubuntu Pro)
- Ubuntu 16.04 LTS (Available with Ubuntu Pro)

Summary:

Several security issues were fixed in X.Org X Server.

Software Description:
- xorg-server: X.Org X11 server

Details:

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.

Original advisory details:

 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.
 (CVE-2023-6377)

 Jan-Niklas Sohn discovered that the X.Org X Server incorrectly handled
 memory when processing the RRChangeOutputProperty and
 RRChangeProviderProperty APIs. An attacker could possibly use this issue to
 cause the X Server to crash, or obtain sensitive information.
 (CVE-2023-6478)

Update instructions:

The problem can be corrected by updating your system to the following
package versions:

Ubuntu 18.04 LTS (Available with Ubuntu Pro):
  xserver-xorg-core               2:1.19.6-1ubuntu4.15+esm3
  xwayland                        2:1.19.6-1ubuntu4.15+esm3

Ubuntu 16.04 LTS (Available with Ubuntu Pro):
  xserver-xorg-core               2:1.18.4-0ubuntu0.12+esm8
  xwayland                        2:1.18.4-0ubuntu0.12+esm8

After a standard system update you need to reboot your computer to make all
the necessary changes.

References:
  https://ubuntu.com/security/notices/USN-6555-2
  https://ubuntu.com/security/notices/USN-6555-1
  CVE-2023-6377, CVE-2023-6478