CVE-2015-3218 in PolicyKit
Summary
by MITRE
The authentication_agent_new function in polkitbackend/polkitbackendinteractiveauthority.c in PolicyKit (aka polkit) before 0.113 allows local users to cause a denial of service (NULL pointer dereference and polkitd daemon crash) by calling RegisterAuthenticationAgent with an invalid object path.
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Analysis
by VulDB Data Team • 06/25/2022
The vulnerability described in CVE-2015-3218 affects PolicyKit, a system-level authorization framework used in Unix-like operating systems to manage user permissions and access controls. This flaw exists within the authentication_agent_new function located in the polkitbackend/polkitbackendinteractiveauthority.c file of the PolicyKit implementation. The issue represents a classic denial of service vulnerability that can be exploited by local attackers to crash the polkitd daemon, effectively disrupting system authorization services and potentially rendering certain administrative functions unavailable. The vulnerability specifically manifests when the RegisterAuthenticationAgent method is invoked with an invalid object path parameter, creating a condition where the system attempts to dereference a NULL pointer during the authentication agent registration process.
The technical exploitation of this vulnerability leverages the lack of proper input validation within the authentication agent registration mechanism. When a local user crafts a malicious call to RegisterAuthenticationAgent with an invalid object path, the polkit backend fails to properly validate the input before attempting to process it. This validation failure leads to a NULL pointer dereference, which in turn causes the polkitd daemon to crash and terminate unexpectedly. The vulnerability demonstrates a clear weakness in the input sanitization and error handling mechanisms within the PolicyKit backend, where the system does not adequately check the legitimacy of object path parameters before proceeding with the authentication agent setup process. This type of vulnerability falls under CWE-476, which specifically addresses NULL pointer dereference conditions in software implementations.
The operational impact of CVE-2015-3218 extends beyond simple service disruption, as it can severely compromise system security and availability. When the polkitd daemon crashes, users lose access to critical authorization mechanisms that control administrative privileges, system configuration changes, and other privileged operations. This disruption can effectively lock users out of legitimate administrative functions while the service is restarting, creating a window of potential security risk where authorization controls may be temporarily weakened or unavailable. The vulnerability is particularly concerning because it allows local users to trigger a daemon crash without requiring elevated privileges, making it an attractive target for attackers seeking to disrupt system operations or create conditions for further exploitation. From an ATT&CK framework perspective, this vulnerability aligns with techniques involving privilege escalation and denial of service, potentially serving as a stepping stone for more sophisticated attacks.
The remediation for this vulnerability requires updating to PolicyKit version 0.113 or later, where the input validation has been properly implemented to prevent NULL pointer dereference conditions. System administrators should prioritize patching this vulnerability as it represents a straightforward fix that addresses the root cause of the issue. Additionally, organizations should implement monitoring for suspicious authentication agent registration attempts and consider implementing additional access controls to limit local user capabilities that could be exploited to trigger such vulnerabilities. The fix typically involves adding proper validation checks for object path parameters before any processing occurs, ensuring that invalid inputs are rejected rather than processed leading to crashes. This vulnerability serves as an example of why robust input validation and error handling should be implemented throughout system components, particularly in authorization frameworks that control critical system access.