# CVE-2026-56000: X.Org xorg-server and xwayland heap use-after-free in GLX CommonMakeCurrent

Source: https://junglewise.ai/threats/cve-2026-56000-x-org-xorg-server-and-xwayland-heap-use-after-free-in-glx  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-07-08. Updated: 2026-07-08  
License: CC BY 4.0 with a link back

CVE-2026-56000 · Severity: info · CVSS 9 · Published 2026-07-08

A vulnerability exists in the X.Org X server and Xwayland, which are fundamental components used to manage graphical displays and windows on Linux and Unix-like systems. A local attacker or a user with an active X connection can trigger a memory error that could lead to a system crash or potentially allow them to execute unauthorized code. This could compromise the stability of the workstation or allow an attacker to gain higher privileges on the system.

Technologies: [X.Org Xorg-Server](https://junglewise.ai/threats/technologies/xorg-server). Vendors: [X.Org](https://junglewise.ai/threats/vendors/x-org).

## Quick answers

**Is CVE-2026-56000 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-56000 being exploited in the wild.

**How severe is CVE-2026-56000?** Informational severity, with a CVSS score of 9, published 8 July 2026.

**Which products and versions are affected?** X.Org Xorg-Server before 21.1.24.

**Is there a fix for CVE-2026-56000?** A patch was published on 2026-05-31: Fix authored in upstream repository Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-56000 attacked?** It is attacked with local access or over the network, in an operating system.

**Am I affected by CVE-2026-56000?** Check whether you run X.Org Xorg-Server 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 heap use-after-free vulnerability exists in the CommonMakeCurrent() function within the GLX dispatch layer of xorg-server and xwayland. The function captures a direct pointer (oldTag) into the per-client cl->contextTags array. If a subsequent call to CommonMakeNewCurrent() triggers a realloc() of the contextTags array (which occurs when the initial 16-slot capacity is exceeded), the oldTag pointer becomes dangling. The subsequent call to GlxFreeContextTag(oldTag) then performs a write-what-where (zeroing five fields at fixed offsets) into freed heap memory. An attacker can trigger this by creating 17 GLX contexts and performing specific MakeCurrent requests. The issue is fixed in xorg-server 21.1.24 and xwayland 24.1.13.

## Affected products

- X.Org xorg-server before 21.1.24
- X.Org xwayland before 24.1.13

## Timeline

- 2026-05-31: patched: Fix authored in upstream repository
- 2026-07-08: advisory: X.Org Security Advisory released
- 2026-07-08: disclosed: Public disclosure on oss-security mailing list

## References

- [https://gitlab.freedesktop.org/xorg/xserver/-/commit/2779affbdb4354e894f490e56f962527d6125043](https://gitlab.freedesktop.org/xorg/xserver/-/commit/2779affbdb4354e894f490e56f962527d6125043)
- [https://www.openwall.com/lists/oss-security/2026/07/08/2](https://www.openwall.com/lists/oss-security/2026/07/08/2)

## Related threats

- [X.Org xorg-server and xwayland heap buffer overflow in glamor font atlas](https://junglewise.ai/threats/cve-2026-55999-x-org-xorg-server-and-xwayland-heap-buffer-overflow-in-glamor)
- [X.Org X server and Xwayland use-after-free in CreateSaverWindow](https://junglewise.ai/threats/cve-2026-50263-x-org-x-server-and-xwayland-use-after-free-in-createsaverwindow)