Xorg-x11-server: xorg-x11-server-xwayland: xorg-x11-server: stack buffer overflow in xkb key types due to unchecked shift levels

Summary

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.

Timeline

1. Jun 5, 2026, 10:31 AM UTCCVE published
2. Jun 9, 2026, 12:00 AM UTCCISA SSVC assessment

   Exploitation: none · Automatable: no · Technical impact: total

3. Sep 28, 2026, 11:46 AM UTCRecord last updated

Affected versions

• xorg-x11-server-Xwayland

  Version range not reported

• xorg-x11-server-Xwayland

  Version range not reported

• tigervnc

  Version range not reported

• xorg-x11-server

  Version range not reported

• tigervnc

  Version range not reported

• xorg-x11-server-Xwayland

  Version range not reported

• xorg-x11-server

  Version range not reported

• tigervnc

  Version range not reported

• xorg-x11-server

  Version range not reported

• tigervnc

  Version range not reported

• xorg-x11-server

  Version range not reported

• tigervnc

  Version range not reported

• xorg-x11-server

  Version range not reported

• xorg-x11-server-Xwayland

  Version range not reported

• tigervnc

  Version range not reported

• xorg-x11-server

  Version range not reported

• xorg-x11-server-Xwayland

  Version range not reported

• tigervnc

  Version range not reported

• xorg-x11-server

  Version range not reported

• xorg-x11-server-Xwayland

  Version range not reported

• tigervnc

  Version range not reported

• xorg-x11-server

  Version range not reported

• xorg-x11-server-Xwayland

  Version range not reported

• tigervnc

  Version range not reported

• xorg-x11-server-Xwayland

  Version range not reported

• xorg-x11-server

  Version range not reported

• tigervnc

  Version range not reported

• xorg-x11-server

  Version range not reported

• xorg-x11-server-Xwayland

  Version range not reported

• tigervnc

  Version range not reported

• xorg-x11-server

  Version range not reported

• xorg-x11-server-Xwayland

  Version range not reported

• tigervnc

  Version range not reported

• xorg-x11-server

  Version range not reported

• xorg-x11-server-Xwayland

  Version range not reported

• tigervnc

  Version range not reported

• xorg-x11-server

  Version range not reported

References 25