CVE-2026-50262: X.Org X Server Out-of-Bounds Read Information Disclosure

Technical summary

The vulnerability exists in __glXDisp_ChangeDrawableAttributes() where incorrect size validation permits an out-of-bounds read (CWE-125). An attacker with local access can specify a client-controlled byte count that exceeds the request buffer, causing the function to read memory outside its intended boundaries. While a code path for out-of-bounds writes exists, it requires byte-swapped client operations which are disabled by default, significantly limiting that attack surface.

Business impact

Exploitation could result in unauthorized disclosure of sensitive information resident in server memory, including cryptographic material, session tokens, or user data depending on memory layout. For organizations deploying X.Org-based desktop environments or remote X11 sessions, this represents a data confidentiality risk. The local requirement and medium CVSS score suggest this is not an immediate critical threat but merits prioritization in environments where untrusted local users have system access.

Affected systems

The vulnerability affects X.Org X server and Xwayland implementations. Red Hat Enterprise Linux systems running affected versions of these display server components are explicitly vulnerable. Other Linux distributions and systems bundling vulnerable X.Org versions may also be impacted; organizations should verify their specific vendor advisories for patch availability and affected version ranges.

Exploitability

This vulnerability requires local access (authenticated user) on the target system and can be exploited without user interaction. The low complexity attack vector means standard tooling and techniques are sufficient for exploitation. The lack of current KEV catalog status indicates active exploitation in the wild has not been formally documented as of the data capture date, but organizations should not interpret this as low priority given the accessibility of the attack.

Remediation

Update X.Org X server and Xwayland to patched versions released by your vendor. Red Hat, and other distribution maintainers have released security updates addressing this issue. Verify against official vendor advisories for your specific product versions and deployment model (server or client). If immediate patching is not feasible, restricting local system access or disabling X11 forwarding for untrusted users provides interim risk reduction.

Patch guidance

Consult your Linux distribution's security advisory for CVE-2026-50262 to identify the corrected package versions. For Red Hat Enterprise Linux systems, patches are available through the standard errata channels. Test updates in a non-production environment before deployment to ensure compatibility with your X11 and Xwayland infrastructure. Verify the patched version resolves both the read and write code paths per vendor documentation.

Detection guidance

Monitor system logs for unusual X server or Xwayland process behavior, including unexpected memory access patterns or crashes. Network-based detection is limited since this is a local vulnerability; focus on host-level intrusion detection rules monitoring X11 protocol anomalies or abnormal drawable attribute changes. Organizations running security scanning tools should ensure these tools are updated to detect vulnerable X.Org versions in inventory scans.

Why prioritize this

Although CVSS 5.5 is moderate, prioritize this vulnerability in environments where untrusted or multi-tenant local users access X11 services or where X11 forwarding is used for remote desktop access. The authentication requirement reduces risk in single-user systems but increases priority for shared workstations, container hosts, or remote access gateways. Information disclosure from memory can have cascading security consequences if sensitive data is exposed.

Risk score, explained

The CVSS 3.1 score of 5.5 reflects a local attack requiring authentication (PR:L), no user interaction, and high confidentiality impact with no integrity or availability impact (C:H/I:N/A:N). The score appropriately captures the risk of unauthorized memory disclosure while accounting for the local-only attack vector. Organizations with defense-in-depth controls limiting local user privileges may adjust their internal risk scoring downward.

Frequently asked questions