A stack-based buffer overflow exists in the font alias resolution code of the X.Org X server and Xwayland due to a mismatch in maximum font name lengths between the X server (256 bytes) and libXfont2 (1024 bytes). When a font alias name length is between 257 and 1023 bytes, the X server copies the name into an undersized stack buffer without proper bounds checking, leading to overflow. This vulnerability (CVE-2026-50256) can cause denial of service via server crash or privilege escalation if the X server runs as root. Red Hat Enterprise Linux versions 8 (>=8 <8.10) and 10 (>=10 <10.2) are affected. Red Hat has released security updates fixing this issue as part of broader xorg-x11-server and Xwayland patches.

Successful exploitation can lead to a denial of service by crashing the X server or privilege escalation if the X server is running with root privileges. The CVSS v3.1 base score is 7.8 (High), reflecting high impact on confidentiality, integrity, and availability. There are no known exploits in the wild at this time.

Red Hat has released official security updates that fix this vulnerability. Users should apply the updates for xorg-x11-server and xorg-x11-server-Xwayland packages as provided in Red Hat Enterprise Linux 8.10 and 10.2 and later. Refer to Red Hat advisories RHSA-2026:26562 and RHSA-2026:26566 and the update instructions at https://access.redhat.com/articles/11258. Applying these updates fully mitigates the vulnerability.