CVE-2026-46150

Technical summary

CVE-2026-46150 is a logic error in the Linux kernel's fanotify permission event handling. The fsnotify_get_mark_safe() function may return false for a mark associated with an unrelated notification group, allowing subsequent permission checks to be bypassed. The fix involves properly skipping detached marks that do not belong to the current group before proceeding with permission event validation. This prevents the premature exit from permission check logic and closes the window for unauthorized file access.

Business impact

Organizations running Linux systems face the risk of local privilege escalation and unauthorized file access. A local user could bypass file access monitoring and permissions, potentially allowing unauthorized data access, modification, or exfiltration. This is particularly concerning in multi-tenant environments, containerized deployments, and systems where fanotify is used to enforce file access policies. The impact is heightened in regulated environments where file access controls are critical compliance requirements.

Affected systems

The Linux kernel is affected by this vulnerability. All kernel versions prior to the fix are potentially vulnerable. Organizations should check their running kernel versions against vendor advisories to determine exposure. Both enterprise and community Linux distributions that include vulnerable kernel versions require patching.

Exploitability

Exploitation requires local access to the affected system; remote exploitation is not possible. The vulnerability requires the attacker to have local user privileges (PR:L per CVSS vector), making it suitable for insider threat scenarios or post-compromise lateral movement. The straightforward nature of the logic error suggests active exploitation is plausible once the vulnerability is widely understood.

Remediation

Apply the latest Linux kernel update from your distribution vendor that includes the fanotify permission event handling fix. Kernel updates typically address this through security patches released in maintenance kernels. Verify the applied kernel version contains the commit that corrects fsnotify_get_mark_safe() behavior for cross-group mark detection.

Patch guidance

Monitor your Linux distribution's security advisory channels for kernel updates addressing fanotify. Most major distributions (Ubuntu, Red Hat, Debian, SUSE, etc.) release kernel updates through their standard patch mechanisms. Prioritize applying updates to systems where fanotify is actively used for file access monitoring. Test updates in non-production environments first to ensure compatibility with your monitoring and security tools before broad deployment.

Detection guidance

Review audit logs and system call traces for unexpected fanotify permission event denials or bypasses on protected files. Monitor for local user activity involving file access to sensitive locations immediately after updates or configuration changes. Correlate fanotify event logs with unauthorized file access incidents. Organizations using EDR or kernel-level monitoring tools should review logs for permission bypass patterns around fanotify-protected resources.

Why prioritize this

This vulnerability merits rapid patching due to its HIGH CVSS score (7.1) and local privilege escalation potential. The logic error in permission event handling directly undermines file access control enforcement, which is critical in security-hardened systems. While exploitation requires local access, the ease of exploitation and the sensitivity of the affected subsystem justify priority treatment in patch management workflows.

Risk score, explained

The CVSS v3.1 score of 7.1 (HIGH) reflects high impact on confidentiality and integrity through local privilege escalation (C:H, I:H) with relatively low attack complexity (AV:L, AC:L, PR:L). The absence of availability impact is noted. The score appropriately reflects the serious nature of bypassing file access permission checks while acknowledging the local access prerequisite.

Frequently asked questions