CVE-2026-98413 in Linux
Summary
by MITRE • 10/14/2026
In the Linux kernel, the following vulnerability has been resolved:
selinux: always fill AVC decision in avc_has_perm_noaudit()
avc_has_perm_noaudit() is documented to return a copy of the access decision in @avd, but its early return for an empty requested permission set leaves the buffer untouched. All callers pass an uninitialized stack variable and afterwards feed it to avc_audit(), and the inode hook even stores it in the per-task decision cache.
Fill in a deny-all, audit-all decision, similar to avd_init(), so every caller receives a defined value at no cost on the hot path.
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Analysis
by VulDB Data Team • 10/14/2026
The Linux Security Modules framework, specifically SELinux, relies heavily on Access Vector Cache mechanisms to enforce mandatory access control policies efficiently. A critical flaw was identified in the implementation of the function avc_has_perm_noaudit within this subsystem. This function is designed to evaluate whether a specific process has permission to perform an action on a target object and subsequently populate a provided structure with the resulting decision. The documentation for this API explicitly states that it returns a copy of the access decision via the output parameter, ensuring that callers receive a definitive result regardless of the outcome. However, the implementation contained a logic error where early exits occurred when the requested permission set was empty or invalid. In these specific scenarios, the function would return without initializing the output buffer, leaving it in an undefined state rather than providing a consistent default decision.
This uninitialized memory issue creates a significant security risk because all callers of this function subsequently pass the potentially garbage-filled structure to avc_audit for logging purposes and store it in per-task decision caches within inode hooks. When unallocated or stale stack data is passed to auditing mechanisms, it can lead to inconsistent log entries that obscure forensic analysis capabilities. More critically, if these uninitialized values are cached as part of task-specific decisions, they may influence future access control evaluations incorrectly. This behavior violates the principle of least privilege by potentially allowing actions based on random memory contents rather than explicit policy denials or allowances, thereby undermining the integrity of the mandatory access control system.
From a technical remediation perspective, the vulnerability was resolved by ensuring that avc_has_perm_noaudit always initializes the output structure with a deny-all and audit-all decision before returning, even when no permissions are requested. This approach mirrors the behavior of avd_init and ensures that every caller receives a well-defined value without imposing performance penalties on the hot path. By standardizing the return state to an explicit denial, the kernel guarantees consistent security posture regardless of edge cases in permission requests. This fix aligns with CWE-908 regarding use of uninitialized resource, addressing the root cause where critical security data was left unpopulated due to premature function exits.
The operational impact of this vulnerability extends beyond mere logging inaccuracies; it affects the reliability of SELinux enforcement across various subsystems that depend on accurate access decision caching. Systems relying on strict audit trails for compliance with standards such as NIST SP 800-53 or CIS benchmarks may find their monitoring capabilities compromised by inconsistent data entries. Furthermore, attackers exploiting race conditions or specific edge cases in permission requests could theoretically manipulate the uninitialized memory to bypass intended restrictions if the garbage values coincidentally matched allowed permissions. The patch ensures deterministic behavior, reinforcing the robustness of the security module against such anomalies and maintaining strict adherence to defined policy rules without performance degradation.