Junglewise Threat Intelligence

CVE-2026-34001: X.Org X server use-after-free in miSyncTriggerFence

CVE-2026-34001 · Severity: high · CVSS 7.8 · Published 2026-04-23

Technologies: X.Org Foundation X Server, X.Org Foundation Xwayland, Tigervnc. Vendors: X.Org Foundation, X.Org, Tigervnc.

Executive brief

A security vulnerability has been identified in the X.Org X server, a fundamental component used to manage graphical displays on Linux and Unix-like systems. An attacker with local access to the system can trigger a specific error in the display synchronization logic to crash the server or potentially gain unauthorized control over the system. This could lead to a total service outage for the graphical interface or allow an attacker to access sensitive data stored in memory.

Technical details

A use-after-free vulnerability exists in the X.Org X server within the miSyncTriggerFence() function of the XSYNC extension. The flaw is triggered during the fence triggering logic when a pointer is accessed after it has been freed (CWE-825). A local attacker with access to the X11 server can exploit this without user interaction. Successful exploitation can result in a denial of service (server crash) or arbitrary code execution via memory corruption. Patches have been released by major distributions including Red Hat for Xwayland and TigerVNC components that incorporate the X.Org server code.

Affected products

  • X.Org X server All versions prior to fixes released in April 2026
  • X.Org Xwayland
  • TigerVNC TigerVNC

Timeline

  • 2026-04-23: disclosed: Initial CVE publication
  • 2026-04-27: patched: Red Hat released fixes for TigerVNC (RHSA-2026:10739)
  • 2026-04-28: patched: Red Hat released fixes for Xwayland (RHSA-2026:11352)

References

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