CVE-2018-15686 in Communications Cloud Native Core Network Function Cloud Native Environment
Summary
by MITRE
A vulnerability in unit_deserialize of systemd allows an attacker to supply arbitrary state across systemd re-execution via NotifyAccess. This can be used to improperly influence systemd execution and possibly lead to root privilege escalation. Affected releases are systemd versions up to and including 239.
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Analysis
by VulDB Data Team • 10/02/2025
The vulnerability identified as CVE-2018-15686 resides within the systemd service manager's unit_deserialize function, representing a critical security flaw that enables arbitrary state injection across systemd re-execution processes. This vulnerability specifically targets the NotifyAccess parameter handling mechanism within systemd's serialization and deserialization processes, creating a pathway for malicious actors to manipulate system behavior through crafted input data. The flaw exists in systemd versions up to and including version 239, making a substantial portion of Linux distributions vulnerable to this attack vector.
The technical exploitation of this vulnerability occurs when systemd processes deserialize unit files containing malicious NotifyAccess configurations. During the re-execution process, the unit_deserialize function fails to properly validate or sanitize the NotifyAccess parameter, allowing attackers to inject arbitrary state information that persists across systemd restarts or re-execution events. This improper state handling creates a persistent backdoor within the system's service management framework, enabling attackers to manipulate how systemd processes are executed and managed. The vulnerability operates at the core of systemd's security model, where legitimate service management operations can be subverted through carefully crafted input data that bypasses normal validation checks.
The operational impact of CVE-2018-15686 extends beyond simple privilege escalation to encompass complete system compromise through the manipulation of critical system services. Attackers can leverage this vulnerability to gain root privileges by injecting malicious state information that influences systemd's execution behavior, potentially allowing them to modify service configurations, inject malicious code into running processes, or manipulate service startup sequences. The vulnerability's severity is amplified by systemd's widespread adoption across modern Linux distributions, where it serves as the primary system and service manager. This means that successful exploitation can affect the entire system's integrity and availability, as systemd controls essential system services and daemon processes.
This vulnerability aligns with CWE-20: Improper Input Validation, specifically manifesting as a failure to properly validate serialized data inputs within the systemd service management framework. The attack pattern follows the MITRE ATT&CK framework's privilege escalation techniques, particularly leveraging the 'Exploitation for Privilege Escalation' tactic. The vulnerability demonstrates characteristics of a command injection flaw where arbitrary state information can be injected into the system's core service management processes, creating persistent access vectors that can be maintained across system reboots. Organizations implementing systemd-based systems face significant risk from this vulnerability, as it enables attackers to establish persistent footholds within their environments while maintaining elevated privileges.
The recommended mitigations for CVE-2018-15686 involve immediate deployment of patched systemd versions, specifically systemd version 240 and later, which contain proper validation mechanisms for the NotifyAccess parameter. System administrators should also implement monitoring for suspicious unit file modifications and consider restricting write access to systemd unit directories. Additionally, organizations should conduct comprehensive vulnerability assessments to identify any systems running affected systemd versions and ensure proper patch management procedures are in place. The vulnerability underscores the importance of input validation in critical system components and highlights the need for robust security practices in service management frameworks that control fundamental system operations.