CVE-2013-4327 in Linux
Summary
by MITRE
systemd does not properly use D-Bus for communication with a polkit authority, which allows local users to bypass intended access restrictions by leveraging a PolkitUnixProcess PolkitSubject race condition via a (1) setuid process or (2) pkexec process, a related issue to CVE-2013-4288.
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Analysis
by VulDB Data Team • 01/08/2022
The vulnerability described in CVE-2013-4327 represents a critical security flaw in systemd's implementation of D-Bus communication with polkit authority components. This issue stems from improper handling of D-Bus message passing mechanisms when interacting with polkit subjects, specifically creating opportunities for local privilege escalation through race condition exploitation. The flaw affects systems where systemd manages service execution and polkit handles authorization decisions, creating a pathway for unauthorized access to privileged operations.
The technical root cause involves a race condition within the PolkitUnixProcess PolkitSubject implementation where systemd fails to properly validate process credentials during D-Bus communication. When a setuid process or pkexec process attempts to perform privileged operations, the timing window between credential validation and actual authorization enforcement allows malicious actors to manipulate the authorization flow. This race condition occurs because systemd's D-Bus interface does not adequately synchronize access to polkit authority components, enabling attackers to exploit temporal inconsistencies in credential verification.
The operational impact of this vulnerability is significant as it allows local users to bypass intended access restrictions without requiring elevated privileges. Attackers can leverage this weakness to execute privileged operations that should normally be restricted to administrators or specific user groups. The vulnerability affects systems running systemd versions that implement the problematic D-Bus communication patterns, potentially compromising entire system security if exploited successfully. The attack vector through setuid processes and pkexec processes makes this particularly dangerous as these are common mechanisms for privilege escalation in Unix-like systems.
This vulnerability aligns with CWE-362, which describes race conditions in security-critical code sections, and relates to the ATT&CK technique T1068, which covers "Exploitation for Privilege Escalation." The issue demonstrates poor implementation of access control mechanisms within the system's service management framework, creating opportunities for unauthorized privilege elevation. Organizations using systemd-based systems are particularly vulnerable, as this flaw can be exploited without requiring network access or specialized knowledge beyond understanding basic Unix privilege models.
Mitigation strategies include updating systemd to versions that properly address the D-Bus communication race condition with polkit authority components. System administrators should also implement additional monitoring for suspicious setuid and pkexec usage patterns, along with regular security audits of system services. The vulnerability highlights the importance of proper synchronization mechanisms in security-critical code paths and underscores the necessity of thorough testing for race conditions in authorization frameworks. Organizations should also consider implementing additional access control measures beyond the default systemd configuration to reduce the attack surface for such privilege escalation techniques.