CVE-2016-7795 in systemd
Summary
by MITRE
The manager_invoke_notify_message function in systemd 231 and earlier allows local users to cause a denial of service (assertion failure and PID 1 hang) via a zero-length message received over a notify socket.
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Analysis
by VulDB Data Team • 09/26/2022
The vulnerability identified as CVE-2016-7795 resides within the systemd service manager implementation and represents a critical local privilege escalation vector that can result in system-wide denial of service conditions. This flaw specifically affects systemd versions 231 and earlier, where the manager_invoke_notify_message function fails to properly handle zero-length messages received through notify sockets. The issue manifests as an assertion failure that ultimately causes PID 1, which is the core systemd process, to hang indefinitely, effectively rendering the entire system unresponsive to service management operations.
The technical root cause of this vulnerability lies in the improper validation of message length within the notify socket communication mechanism. When a zero-length message is transmitted to the systemd manager through the notify socket interface, the function does not perform adequate bounds checking or length validation before attempting to process the message. This absence of input sanitization creates a condition where the system's assertion mechanisms trigger unexpectedly, leading to a cascade failure that prevents the manager process from continuing normal operations. The flaw operates at the kernel-level interface between user-space applications and the systemd daemon, leveraging the standard notify socket protocol that systemd uses for service status updates and communication.
From an operational perspective, this vulnerability presents significant risks to system stability and availability. Since PID 1 represents the systemd init process, any hang or failure in this critical component results in complete system service disruption. Local attackers with minimal privileges can exploit this weakness to cause persistent denial of service conditions that require manual intervention to resolve, including system reboots or manual PID 1 process termination. The impact extends beyond simple service disruption as it affects the entire system management infrastructure, potentially compromising system integrity and availability for legitimate users and applications relying on proper service management.
The vulnerability aligns with CWE-129, which addresses improper validation of input length, and demonstrates characteristics consistent with the ATT&CK technique T1499.004 for network denial of service. Organizations running affected systemd versions face potential operational risks including service outages, system unavailability, and increased attack surface for more sophisticated exploitation attempts. The flaw particularly impacts enterprise environments where systemd is the primary service manager, as it can be leveraged to disrupt critical infrastructure services. System administrators should prioritize patching affected systems and implementing monitoring solutions to detect potential exploitation attempts, while also reviewing service configurations to minimize the attack surface through proper socket access controls and privilege separation mechanisms.
Mitigation strategies should include immediate deployment of systemd patches addressing this specific assertion failure, implementation of proper input validation at all communication interfaces, and establishment of monitoring protocols to detect anomalous notify socket activity. Additionally, organizations should consider implementing privilege separation techniques and access controls to limit local user capabilities that could exploit this vulnerability, while maintaining regular security assessments to identify similar weaknesses in system management components.