CVE-2016-9256 in BIG-IP
Summary
by MITRE
In F5 BIG-IP 12.1.0 through 12.1.2, permissions enforced by iControl can lag behind the actual permissions assigned to a user if the role_map is not reloaded between the time the permissions are changed and the time of the user's next request. This is a race condition that occurs rarely in normal usage; the typical period in which this is possible is limited to at most a few seconds after the permission change.
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Analysis
by VulDB Data Team • 12/06/2022
The vulnerability described in CVE-2016-9256 represents a critical access control flaw within the F5 BIG-IP system's iControl interface, specifically affecting versions 12.1.0 through 12.1.2. This issue manifests as a race condition that undermines the integrity of the system's permission enforcement mechanism, creating potential security risks for organizations relying on F5's application delivery controllers for network traffic management and security. The vulnerability resides in the role_map reloading process, which is responsible for synchronizing user permissions with the system's access control policies. When administrators modify user permissions, the system should immediately reflect these changes through proper role_map reloading, but this synchronization process fails to complete in a timely manner, creating a window of opportunity for unauthorized access.
The technical nature of this vulnerability stems from the asynchronous behavior of the iControl interface's permission management system. When a user's access rights are modified, the system maintains a cached version of the role_map that contains the current permission assignments. However, due to the race condition, the cached permissions may not be updated before the user makes their next request, allowing the user to potentially operate with stale permissions. This race condition typically occurs within a few seconds after permission changes, making it a temporal vulnerability that depends on the timing of administrative actions versus user activity. The flaw is classified under CWE-362, which specifically addresses race conditions in security-critical operations, and aligns with ATT&CK technique T1078.004 for valid accounts, as it exploits legitimate user access through improper permission enforcement rather than bypassing authentication mechanisms directly.
The operational impact of this vulnerability extends beyond simple permission misalignment, potentially enabling attackers with access to legitimate user accounts to perform unauthorized actions within the system. If an attacker can time their requests to coincide with the window when stale permissions are still active, they may be able to execute operations that should be restricted based on their current role assignments. This risk is particularly concerning for organizations that frequently modify user permissions or have dynamic access control requirements, as the window of vulnerability increases with the frequency of permission changes. The limited temporal scope of the vulnerability means that while it can be exploited, it requires precise timing and is not a persistent backdoor. However, the rarity of occurrence in normal usage does not diminish its potential impact when it does occur, as the affected systems may be operating with elevated privileges that could be leveraged for further compromise.
Organizations should implement immediate mitigations including prompt role_map reloading procedures whenever permission changes occur, monitoring for unusual access patterns that might indicate exploitation attempts, and maintaining strict change management protocols for user access rights. The recommended approach involves ensuring that permission modifications are immediately followed by explicit role_map reload operations to eliminate the race condition window. Additionally, system administrators should implement comprehensive logging and alerting mechanisms to detect any unauthorized access attempts that might exploit this vulnerability, particularly during periods of active permission changes. Regular system updates and patches should be applied immediately upon availability, as this vulnerability specifically affects the mentioned F5 BIG-IP versions and is likely addressed in subsequent releases. The vulnerability also highlights the importance of proper system architecture design that minimizes race conditions in security-critical components, aligning with security best practices that emphasize the need for atomic operations in permission management systems.