CVE-2026-50257

Description

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.

CVSS Vector

References

• https://access.redhat.com/security/cve/CVE-2026-50257
• https://bugzilla.redhat.com/show_bug.cgi?id=2485382
• https://gitlab.freedesktop.org/xorg/xserver/-/commit/f5abfb61994471023d8c6470428c8e30c411cc0b
• https://lists.x.org/archives/xorg-announce/2026-June/003702.html
• https://redhat.atlassian.net/browse/PSIRTSUPT-16950