CVE-2018-14600: Canonical Ubuntu Linux

Critical severity, CVSS 9.8. EPSS: 9.3% chance of exploitation in the next 30 days.

An issue was discovered in libX11 through 1.6.5. The function XListExtensions in ListExt.c interprets a variable as signed instead of unsigned, resulting in an out-of-bounds write (of up to 128 bytes), leading to DoS or remote code execution.

Affected products

• Canonical Ubuntu Linux: version 12.04 only; version 14.04 only; version 16.04 only; version 18.04 only
• Debian Debian Linux: version 8.0 only
• X.org LIBX11: up to and including 1.6.5

Published 2018-08-24. Last modified 2026-06-17.