PatchSiren cyber security CVE debrief

CVE-2026-50258 Red Hat CVE debrief

CVE-2026-50258 is a HIGH severity vulnerability in X.Org X server and Xwayland, with a CVSS score of 7.8. 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.

Vendor: Red Hat
Product: Red Hat Enterprise Linux 10
CVSS: HIGH 7.8
CISA KEV: Not listed in stored evidence
Original CVE published: 2026-06-05
Original CVE updated: 2026-08-05
Advisory published: 2026-06-05
Advisory updated: 2026-08-05

Who should care

Users of X.Org X server and Xwayland should apply patches or mitigations to prevent exploitation.

Technical summary

The vulnerability exists in the X.Org X server and Xwayland due to a stack-based buffer overflow flaw. The X server has multiple stack buffers sized XkbMaxShiftLevel * XkbNumKbdGroups but CheckKeyTypes() does not verify or clamp non-canonical key types to XkbMaxShiftLevel.

Defensive priority

HIGH

Recommended defensive actions

Apply patches or updates from vendors
Restrict access to the X server
Monitor for suspicious activity

Evidence notes

The vulnerability was caused by an incomplete fix of CVE-2025-26597.

Sources and references

Verified primary and authoritative sources

CVE-2026-50258 CVE Program record
Publisher, destination, and source semantics verified

URL: https://www.cve.org/CVERecord?id=CVE-2026-50258

CVE Program - Official CVE Program record with source-provided CVE metadata.
CVE-2026-50258 NVD vulnerability detail
Publisher, destination, and source semantics verified

URL: https://nvd.nist.gov/vuln/detail/CVE-2026-50258

NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

Mitigation or vendor reference
Unverified legacy reference

URL: https://access.redhat.com/security/cve/CVE-2026-50258

[email protected] - Third Party Advisory
Mitigation or vendor reference
Unverified legacy reference

URL: https://gitlab.freedesktop.org/xorg/xserver/-/commit/543e108516428fc8c3bea91d6563ad266f9a801e

[email protected] - Patch
Mitigation or vendor reference
Unverified legacy reference

URL: https://lists.x.org/archives/xorg-announce/2026-June/003702.html

[email protected] - Mailing List, Third Party Advisory
Source reference
Unverified legacy reference

URL: https://redhat.atlassian.net/browse/PSIRTSUPT-16950

[email protected] - Permissions Required

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.