CVE-2026-50256: Xorg-x11-server: xorg-x11-server-xwayland: xorg-x11-server: stack buffer overflow in font alias resolution due to libxfont2 name length mismatch

Severity: high (CVSS 7.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-06-05 · updated 2026-08-05
Weakness: CWE-121

Description

A stack-based buffer overflow flaw was found in the X.Org X server and Xwayland. A mismatch between the X server and the libXfont2 library's maximum font name length can cause a stack buffer overflow during font alias resolution. The server allocates a 256 byte stack buffer but libXfont2's alias target name length is 1024 bytes. A font alias name between 257 and 1023 bytes causes the X server to copy that name into the undersized stack buffer without further checks. This may be used to crash the server, or for privilege escalation if the X server runs as root.

Affected products

Red Hat Enterprise Linux: 7.0, 8.0, 9.0, 10.0
xorg-x11-server: before 21.1.23 — fixed in 21.1.23
X.Org xwayland: before 24.1.12 — fixed in 24.1.12

How to fix

Upgrade to a fixed version: xorg-x11-server 21.1.23; X.Org xwayland 24.1.12. Check the vendor advisory for mitigations.

References

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