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

Source: https://junglewise.ai/threats/cve-2026-34001-x-org-x-server-use-after-free-in-misynctriggerfence  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-04-23. Updated: 2026-05-19  
License: CC BY 4.0 with a link back

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

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.

Technologies: [Tigervnc](https://junglewise.ai/threats/technologies/tigervnc), [X.Org Foundation X Server](https://junglewise.ai/threats/technologies/x-server), [X.Org Foundation Xwayland](https://junglewise.ai/threats/technologies/xwayland). Vendors: [Tigervnc](https://junglewise.ai/threats/vendors/tigervnc), [X.Org Foundation](https://junglewise.ai/threats/vendors/x-org-foundation).

## Quick answers

**Is CVE-2026-34001 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-34001 being exploited in the wild.

**How severe is CVE-2026-34001?** High severity, with a CVSS score of 7.8, published 23 April 2026.

**Which products and versions are affected?** X.Org Foundation X Server All versions prior to fixes released in April 2026.

**Is there a fix for CVE-2026-34001?** A patch was published on 2026-04-27: Red Hat released fixes for TigerVNC (RHSA-2026:10739) Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-34001 attacked?** It is attacked with local access, in an operating system.

**Am I affected by CVE-2026-34001?** Check whether you run Tigervnc, X.Org Foundation X Server or X.Org Foundation Xwayland at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## 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

- [https://access.redhat.com/errata/RHSA-2026:10739](https://access.redhat.com/errata/RHSA-2026:10739)
- [https://access.redhat.com/errata/RHSA-2026:11352](https://access.redhat.com/errata/RHSA-2026:11352)
- [https://access.redhat.com/errata/RHSA-2026:11369](https://access.redhat.com/errata/RHSA-2026:11369)
- [https://access.redhat.com/errata/RHSA-2026:11388](https://access.redhat.com/errata/RHSA-2026:11388)
- [https://access.redhat.com/errata/RHSA-2026:11656](https://access.redhat.com/errata/RHSA-2026:11656)
- [https://access.redhat.com/errata/RHSA-2026:11692](https://access.redhat.com/errata/RHSA-2026:11692)
- [https://access.redhat.com/errata/RHSA-2026:13414](https://access.redhat.com/errata/RHSA-2026:13414)

## Related threats

- [X.Org X Server double free in XKB SetGeometry](https://junglewise.ai/threats/cve-2026-88812-a-double-free-in-xkb-setgeometryin-x-org-x-server-before-21-1-25)
- [X.Org X server use-after-free in SyncChangeCounter](https://junglewise.ai/threats/cve-2026-50261-x-org-x-server-use-after-free-in-syncchangecounter)
- [X.Org X server and Xwayland use-after-free in FreeCounter](https://junglewise.ai/threats/cve-2026-50260-x-org-x-server-and-xwayland-use-after-free-in-freecounter)
- [X.Org X server stack buffer overflow in XKB SetMap request](https://junglewise.ai/threats/cve-2026-50259-x-org-x-server-stack-buffer-overflow-in-xkb-setmap-request)
- [X.Org X server out-of-bounds read in XKB geometry processing](https://junglewise.ai/threats/cve-2026-34000-x-org-x-server-out-of-bounds-read-in-xkb-geometry-processing)