CVE-2025-26595 is a high-severity stack-based buffer overflow vulnerability found in the XkbVModMaskText() function of X.Org and Xwayland. The function copies virtual modifier names into a fixed-size stack buffer without validating the size, which can cause a buffer overflow. This flaw affects versions up to 22.0.0 and has a CVSS 3.1 base score of 7.8 (AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H), indicating local attack vector with low complexity and requiring low privileges, no user interaction, and resulting in high impact on confidentiality, integrity, and availability. Red Hat has released security advisories RHSA-2025:2500 and RHSA-2025:2502, providing patched tigervnc packages for Red Hat Enterprise Linux 8 and 9 that fix this and other related vulnerabilities in X.Org/Xwayland components. The advisories include detailed package versions and instructions for applying the updates.

Successful exploitation of this vulnerability could allow a local attacker with low privileges to cause a buffer overflow in X.Org/Xwayland, potentially leading to arbitrary code execution or denial of service. The CVSS score of 7.8 reflects high impact on confidentiality, integrity, and availability. However, no known exploits in the wild have been reported at this time.

Red Hat has released official patches for this vulnerability as part of updated tigervnc packages for Red Hat Enterprise Linux versions 8 and 9. Users should apply these updates promptly following the guidance in Red Hat advisories RHSA-2025:2500 and RHSA-2025:2502 and the instructions at https://access.redhat.com/articles/11258. Applying these official fixes fully mitigates the vulnerability. No additional mitigation steps are required beyond applying the vendor-provided patches.