CVE-2001-0040 in apcupsd
Summary
by MITRE
APC UPS daemon, apcupsd, saves its process ID in a world-writable file, which allows local users to kill an arbitrary process by specifying the target process ID in the apcupsd.pid file.
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Analysis
by VulDB Data Team • 09/21/2024
The vulnerability described in CVE-2001-0040 affects the APC UPS daemon known as apcupsd which is commonly used to manage uninterruptible power supply systems in computing environments. This daemon is responsible for monitoring power conditions and managing system shutdown procedures during power failures. The core issue stems from the daemon's improper handling of its process identification file, specifically the apcupsd.pid file that it creates during operation. The daemon writes its own process identifier to this file without proper access controls, resulting in a world-writable file that can be modified by any local user on the system.
The technical flaw represents a classic privilege escalation vulnerability where a local attacker can manipulate the process ID stored in the apcupsd.pid file to target any running process on the system. When the apcupsd daemon attempts to read this file during its operation, it will execute commands against the process ID specified in the file rather than its own legitimate process. This creates an opportunity for malicious users to cause arbitrary process termination by simply modifying the PID file to contain the process ID of a target process they wish to kill. The vulnerability essentially allows for process injection and manipulation through a simple file modification attack.
The operational impact of this vulnerability is significant for system security and availability. Local users with minimal privileges can exploit this weakness to disrupt critical system services by terminating essential processes such as system daemons, network services, or even the apcupsd daemon itself. This creates a potential denial of service scenario where an attacker can systematically kill processes to destabilize system operations or gain further access to the system through service disruption. The vulnerability also enables more sophisticated attacks where an attacker might target specific processes to disable security mechanisms or create conditions favorable for additional exploitation. According to CWE classification, this represents a CWE-276: Improper File Permissions for Critical Resources, which directly relates to inadequate access control measures for system files.
The attack surface for this vulnerability is primarily local, as it requires physical or authenticated access to the system where apcupsd is running. However, the impact can be severe because it provides attackers with a mechanism to manipulate running processes without requiring elevated privileges. From an ATT&CK framework perspective, this vulnerability maps to techniques involving privilege escalation and process injection, specifically T1068: Exploitation for Privilege Escalation and T1059: Command and Scripting Interpreter. The vulnerability also aligns with T1489: Service Stop, as it allows for the termination of system services through manipulation of process identification files. Organizations should implement proper file permissions for the apcupsd.pid file, ensuring that only the apcupsd process has write access to it while maintaining appropriate read permissions for system administrators. Additionally, system monitoring should be implemented to detect unauthorized modifications to critical system files. The recommended mitigation involves configuring the daemon to create the PID file with restrictive permissions and implementing proper file integrity monitoring to detect any unauthorized changes to critical system resources.