Bug 2485382 (CVE-2026-50257) - CVE-2026-50257 xorg-x11-server: xorg-x11-server-Xwayland: xorg-x11-server: use-after-free in miSyncDestroyFence()
Summary: CVE-2026-50257 xorg-x11-server: xorg-x11-server-Xwayland: xorg-x11-server: us...
Keywords:
Status: NEW
Alias: CVE-2026-50257
Product: Security Response
Classification: Other
Component: vulnerability
Version: unspecified
Hardware: All
OS: Linux
high
high
Target Milestone: ---
Assignee: Product Security DevOps Team
QA Contact:
URL:
Whiteboard:
Depends On:
Blocks:
TreeView+ depends on / blocked
 
Reported: 2026-06-05 08:11 UTC by OSIDB Bzimport
Modified: 2026-06-05 10:30 UTC (History)
2 users (show)

Fixed In Version:
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Description OSIDB Bzimport 2026-06-05 08:11:51 UTC 
A client that sets up multiple fence triggers can trigger a use-after-free function pointer call in miSyncDestroyFence(). An attacker connects to the X server to set up a fence and awaits that fence, then a second X connection destroys the fence, causing the use-after-free.

Any X client that can connect to the server can trigger this issue. This may be used to crash the server, or for privilege escalation if the X server runs as root.

Components affected: xorg-x11-server, xorg-x11-server-Xwayland
Versions affected: xorg-x11-server <= 21.1.22, xorg-x11-server-Xwayland <= 24.1.9

Fixed upstream in xorg-server-21.1.23 and xwayland-24.1.12.
Fix: https://gitlab.freedesktop.org/xorg/xserver/-/commit/f5abfb61994471023d8c6470428c8e30c411cc0b

Reported via ZDI-CAN-30159 (Trend Micro Zero Day Initiative). Tracking: PSIRTSUPT-16950.
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