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Ubuntu Security Notice USN-6407-2
October 10, 2023

libx11 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)
- Ubuntu 14.04 LTS (Available with Ubuntu Pro)

Summary:

Several security issues were fixed in libx11.

Software Description:
- libx11: X11 client-side library

Details:

USN-6407-1 fixed several vulnerabilities in libx11. This update provides
the corresponding update for Ubuntu 14.04 LTS, Ubuntu 16.04 LTS and Ubuntu 18.04 LTS.

Original advisory details:

 Gregory James Duck discovered that libx11 incorrectly handled certain
 keyboard symbols. If a user were tricked into connecting to a malicious X
 server, a remote attacker could use this issue to cause libx11 to crash,
 resulting in a denial of service, or possibly execute arbitrary code.
 (CVE-2023-43785)

 Yair Mizrahi discovered that libx11 incorrectly handled certain malformed
 XPM image files. If a user were tricked into opening a specially crafted
 XPM image file, a remote attacker could possibly use this issue to consume
 memory, leading to a denial of service. (CVE-2023-43786)

 Yair Mizrahi discovered that libx11 incorrectly handled certain malformed
 XPM image files. If a user were tricked into opening a specially crafted
 XPM image file, a remote attacker could use this issue to cause libx11 to
 crash, leading to a denial of service, or possibly execute arbitrary code.
 (CVE-2023-43787)

Update instructions:

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

Ubuntu 18.04 LTS (Available with Ubuntu Pro):
  libx11-6                        2:1.6.4-3ubuntu0.4+esm2

Ubuntu 16.04 LTS (Available with Ubuntu Pro):
  libx11-6                        2:1.6.3-1ubuntu2.2+esm4

Ubuntu 14.04 LTS (Available with Ubuntu Pro):
  libx11-6                        2:1.6.2-1ubuntu2.1+esm5

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

References:
  https://ubuntu.com/security/notices/USN-6407-2
  https://ubuntu.com/security/notices/USN-6407-1
  CVE-2023-43785, CVE-2023-43786, CVE-2023-43787