CVE-2026-50258

Description

A stack-based buffer overflow flaw was found in the X.Org X server and Xwayland. The X server has multiple stack buffers sized XkbMaxShiftLevel * XkbNumKbdGroups but CheckKeyTypes() does not verify or clamp non-canonical key types to XkbMaxShiftLevel. A client can change key types to excessive shift levels and trigger stack overflows. This is caused by an incomplete fix of CVE-2025-26597. This may be used to crash the server, or for privilege escalation if the X server runs as root.

CVSS Vector

References

• https://access.redhat.com/security/cve/CVE-2026-50258
• https://bugzilla.redhat.com/show_bug.cgi?id=2485383
• https://gitlab.freedesktop.org/xorg/xserver/-/commit/543e108516428fc8c3bea91d6563ad266f9a801e
• https://lists.x.org/archives/xorg-announce/2026-June/003702.html
• https://redhat.atlassian.net/browse/PSIRTSUPT-16950