CVE-2017-14681 in P3Scan
Summary
by MITRE
The daemon in P3Scan 3.0_rc1 and earlier creates a p3scan.pid file after dropping privileges to a non-root account, which might allow local users to kill arbitrary processes by leveraging access to this non-root account for p3scan.pid modification before a root script executes a "kill `cat /pathname/p3scan.pid`" command, as demonstrated by etc/init.d/p3scan.
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Analysis
by VulDB Data Team • 11/18/2019
The vulnerability identified as CVE-2017-14681 resides within the P3Scan email scanning daemon version 3.0_rc1 and earlier, presenting a critical privilege escalation risk through improper file handling during the daemon startup process. This flaw manifests when the daemon creates a p3scan.pid file while operating under non-root privileges, establishing a persistent file that can be manipulated by local users who have access to the non-root account. The issue stems from the daemon's failure to properly secure the pid file's location and permissions, creating a race condition that allows malicious users to substitute their own process ID into the file before the root script executes its kill command.
The technical exploitation of this vulnerability follows a well-defined pattern that leverages the daemon's privilege dropping mechanism and subsequent pid file creation. When P3Scan drops privileges from root to a non-root account, it continues to write the pid file to a location that can be modified by users with access to the non-root account. This creates a window of opportunity where an attacker can modify the p3scan.pid file to contain a process ID belonging to another running process, particularly one that the attacker wishes to terminate or manipulate. The root script located at etc/init.d/p3scan executes a command that reads the pid file and issues a kill signal to the process ID contained within, effectively allowing the local user to kill arbitrary processes on the system.
This vulnerability directly maps to CWE-276, which addresses improper file permissions, and CWE-362, which covers concurrent execution of potentially conflicting operations. The flaw represents a classic race condition scenario where the timing between privilege dropping and file creation creates a security gap. From an operational perspective, this vulnerability enables local users to escalate their privileges and potentially compromise system integrity by targeting critical system processes. The attack vector is particularly dangerous because it requires minimal privileges to exploit, as the attacker only needs access to the non-root account used by the daemon, which is typically a standard requirement for daemon operation.
The impact of this vulnerability extends beyond simple process termination, as it can be leveraged to disrupt system services, compromise security mechanisms, or create backdoor access points. The attack follows the ATT&CK technique T1068, which describes the use of privilege escalation to gain access to higher-level system functions. Organizations running affected versions of P3Scan face significant risk, as local users can potentially target critical system processes such as network services, logging daemons, or security monitoring tools. The vulnerability is particularly concerning in multi-user environments where daemon accounts may be accessible to users who should not have such privileges.
Mitigation strategies for CVE-2017-14681 focus on addressing the root cause through proper privilege management and file handling practices. The most effective solution involves ensuring that the p3scan.pid file is created with appropriate permissions and ownership before the daemon drops privileges, preventing modification by unauthorized users. Additionally, implementing proper file locking mechanisms or using atomic file creation techniques can prevent the race condition that enables exploitation. System administrators should also consider upgrading to P3Scan versions that have addressed this vulnerability, as the original issue has been resolved in later releases. Security monitoring should include detection of unauthorized modifications to daemon pid files, particularly those associated with system services that run with elevated privileges. The remediation process should also involve reviewing and hardening the privilege separation mechanisms used by the daemon to ensure that file creation and modification operations cannot be exploited by local users.