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.
| Score | Percentile |
|---|---|
| 0.16% | 5.70% |
| Base score | Version | Severity | Vector |
|---|---|---|---|
| 7.8 | 3.1 | — |
|
| Type | Value |
|---|---|
| GHSA | GHSA-74fp-pmv2-rh3f ↗ |
| CVE | CVE-2026-50258 ↗ |
| CWE id | Name |
|---|---|
| CWE-121 | Stack-based Buffer Overflow |