CVE-2026-50257: Red Hat Enterprise Linux

High severity, CVSS 7.8. EPSS: 0.2% chance of exploitation in the next 30 days.

A use-after-free flaw was found in the X.Org X server and Xwayland in miSyncDestroyFence(). A client that sets up multiple fence triggers can trigger a use-after-free function pointer call. An attacker would connect to the X server to set up a fence and await that fence, then a second X connection destroys the fence, causing the use-after-free. This may be used to crash the server, or for privilege escalation if the X server runs as root.

Affected products

• Red Hat Enterprise Linux: version 7.0 only; version 8.0 only; version 9.0 only; version 10.0 only
• X.org X Server: before 21.1.23 (fixed in 21.1.23)
• X.org Xwayland: before 24.1.12 (fixed in 24.1.12)

Published 2026-06-05. Last modified 2026-08-05.