High · published June 5, 2026
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.
| Product | Versions | Fixed in |
|---|---|---|
| x.org/x_server | < 21.1.23 | 21.1.23 |
| x.org/xwayland | < 24.1.12 | 24.1.12 |
| redhat/enterprise_linux | all versions | — |
| redhat/enterprise_linux | all versions | — |
| redhat/enterprise_linux | all versions | — |
| redhat/enterprise_linux | all versions | — |