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CVE-2026-50258

HIGH · CVSS 7.8EPSS 0.2%EU EUVD

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.

Key facts

CVSS score
7.8 (v3.1)
Severity
HIGH
CVSS vector
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Weakness (CWE)
CWE-121
EPSS score
0.2% (12th percentile)
In CISA KEV
No
In EU EUVD
Yes (EUVD-2026-34815)
Published
June 5, 2026
NVD last modified
August 5, 2026
Status
Modified

EU Vulnerability Database (EUVD)

This vulnerability is also tracked by ENISA as EUVD-2026-34815 in the EU Vulnerability Database. Last updated in EUVD on September 28, 2026.

View on the EU Vulnerability Database

Affected products

  • redhat / enterprise linux
  • redhat / enterprise linux
  • redhat / enterprise linux
  • redhat / enterprise linux
  • x.org / x server
  • x.org / xwayland

Certified products that may be affected

31 FIPS 140 or Common Criteria certified products, from automated matching by sec-certs.org.

See all 31 in the Security Certifications Explorer.

References

Last updated September 17, 2026 · Source: NVD, CISA KEV, FIRST.org EPSS

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