CVE-2015-4625 in PolicyKit
Summary
by MITRE
Integer overflow in the authentication_agent_new_cookie function in PolicyKit (aka polkit) before 0.113 allows local users to gain privileges by creating a large number of connections, which triggers the issuance of a duplicate cookie value.
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Analysis
by VulDB Data Team • 06/25/2022
The vulnerability identified as CVE-2015-4625 represents a critical integer overflow flaw within the PolicyKit authentication system, specifically affecting the authentication_agent_new_cookie function in versions prior to 0.113. This issue resides in the core privilege management framework that governs how applications request and receive elevated permissions on Unix-like operating systems. PolicyKit serves as a central authorization framework that bridges the gap between user sessions and system-level operations, making it a prime target for privilege escalation attacks. The flaw manifests when local users exploit the function's handling of connection counts, leading to predictable cookie value generation that can be manipulated for malicious purposes.
The technical implementation of this vulnerability stems from improper integer overflow handling within the authentication_agent_new_cookie function where consecutive connection attempts can cause the internal counter to wrap around, resulting in duplicate cookie values being issued. This occurs because the system fails to properly validate or constrain the number of connections that can be established before cookie generation, allowing attackers to calculate and predict when the integer will overflow. When the integer reaches its maximum value and wraps to zero, the system may reuse previously issued cookie values, creating a scenario where multiple authentication sessions can share the same cryptographic identifier. This predictable behavior violates fundamental security principles of authentication systems and creates opportunities for session hijacking or privilege escalation attacks.
The operational impact of this vulnerability extends beyond simple local privilege escalation to potentially compromise entire system security postures. Local attackers can leverage this flaw to gain elevated privileges without requiring additional authentication mechanisms, effectively bypassing the layered security controls that PolicyKit is designed to enforce. The vulnerability affects systems where PolicyKit is actively used for privilege management, which includes most modern Linux distributions and Unix-like systems that implement this authorization framework. Attackers can systematically create multiple connections until the integer overflow occurs, then exploit the duplicate cookie values to perform unauthorized actions that should require elevated privileges. This vulnerability aligns with CWE-190, which specifically addresses integer overflow conditions, and represents a classic example of how improper input validation can lead to security breaches in authentication systems.
Mitigation strategies for CVE-2015-4625 primarily focus on immediate software updates and system hardening measures. Organizations should prioritize upgrading to PolicyKit version 0.113 or later, where the integer overflow has been properly addressed through enhanced input validation and counter management. Additionally, system administrators should implement monitoring for unusual connection patterns that might indicate exploitation attempts, particularly around the threshold where integer overflow occurs. The vulnerability demonstrates the importance of proper integer handling in security-critical code and aligns with ATT&CK technique T1068, which covers privilege escalation through local exploits. Network segmentation and limiting local user access to systems running PolicyKit can provide additional defense-in-depth measures, though the most effective solution remains the immediate application of vendor patches and updates to address the root cause of the integer overflow condition.
The broader implications of this vulnerability highlight the critical importance of robust input validation in authentication systems and the potential for seemingly minor implementation flaws to create significant security risks. This flaw exemplifies how authentication frameworks that handle sensitive privilege operations must be rigorously tested for edge cases, particularly around integer handling and resource management. The vulnerability also underscores the necessity of continuous security auditing of core system components, as PolicyKit serves as a fundamental building block for many security mechanisms in modern operating systems. Organizations should conduct comprehensive vulnerability assessments to identify other potential integer overflow conditions within their authentication and authorization systems, ensuring that similar flaws do not exist in other components of their security infrastructure.