CVE-2026-50259: X.Org X server stack buffer overflow in XKB SetMap request

CVE-2026-50259 · Severity: high · CVSS 7.8 · Published 2026-06-05

A security vulnerability has been identified in the X.Org X server and Xwayland, components responsible for managing graphical displays on Linux and Unix-like systems. An attacker with local access to a system can exploit this flaw to crash the display server or potentially gain administrative (root) privileges. This could lead to a full system takeover or a denial of service for all users on the affected machine.

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

Quick answers

Is CVE-2026-50259 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-50259 being exploited in the wild.
How severe is CVE-2026-50259?
High severity, with a CVSS score of 7.8, published 5 June 2026.
Which products and versions are affected?
X.Org Foundation X Server <= 21.1.22; X.Org Foundation Xwayland <= 24.1.9.
Is there a fix for CVE-2026-50259?
A patch was published on 2026-04-20: Upstream fix committed to GitLab Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-50259 attacked?
It is attacked with local access, in an operating system.
Am I affected by CVE-2026-50259?
Check whether you run 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 stack-based buffer overflow exists in the _XkbSetMapChecks() function within the X.Org X server and Xwayland. The function declares a fixed-size stack buffer, mapWidths[256], which is indexed by a key type index. A helper function, CheckKeyTypes(), fails to properly validate or clamp the 'nMaps' value (derived from client-controlled 'firstType' and 'nTypes' fields) when the XkbSetMapResizeTypes flag is set. By sending specifically crafted SetMap requests, a local attacker can bypass index checks and write past the buffer boundaries into adjacent stack variables. This can result in a server crash or arbitrary code execution with the privileges of the X server (often root). The issue is fixed in xorg-server 21.1.23 and xwayland 24.1.12.

Affected products

  • X.Org X server <= 21.1.22
  • X.Org Xwayland <= 24.1.9

Timeline

  • 2026-04-20: patched: Upstream fix committed to GitLab
  • 2026-06-02: advisory: X.Org Security Advisory released
  • 2026-06-05: disclosed: CVE published and NVD record created

References

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