CVE-2001-0905 in Procmail
Summary
by MITRE
Race condition in signal handling of procmail 3.20 and earlier, when running setuid, allows local users to cause a denial of service or gain root privileges by sending a signal while a signal handling routine is already running.
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Analysis
by VulDB Data Team • 04/22/2019
The vulnerability identified as CVE-2001-0905 represents a critical race condition in the signal handling mechanism of procmail version 3.20 and earlier when operating in setuid mode. This flaw exists within the mail delivery agent's signal processing logic where multiple signals can be handled concurrently, creating a window of opportunity for malicious exploitation. The vulnerability specifically manifests when procmail is executed with elevated privileges through setuid permissions, making it a prime target for privilege escalation attacks.
The technical implementation of this race condition stems from the improper synchronization of signal handlers within procmail's execution environment. When a signal is received while another signal handler is already in progress, the application fails to properly queue or defer subsequent signal processing. This condition creates a scenario where concurrent signal handling can lead to memory corruption or unexpected program behavior. The flaw is particularly dangerous because it occurs in a setuid context where the process maintains elevated privileges, allowing an attacker to manipulate the signal handling sequence to achieve unauthorized system access.
The operational impact of this vulnerability extends beyond simple denial of service to include potential privilege escalation to root level access. Local users can exploit this condition by carefully timing signal delivery to trigger the race condition during critical signal handling operations. The vulnerability can be leveraged to either cause the mail delivery process to crash and terminate, thereby denying service to legitimate users, or more critically to execute arbitrary code with root privileges through manipulation of the signal handling state. This dual nature makes the vulnerability particularly attractive to attackers seeking system compromise.
Mitigation strategies for this vulnerability require immediate patching of procmail installations to versions that address the race condition in signal handling. System administrators should ensure that all procmail installations are updated to versions containing proper signal handling synchronization mechanisms. Additionally, implementing proper signal masking and blocking during critical sections of code can prevent the race condition from occurring. The vulnerability aligns with CWE-362 which describes Concurrent Execution using Shared Resource with Improper Synchronization, and maps to ATT&CK technique T1068 which covers Exploitation for Privilege Escalation. Organizations should also consider implementing monitoring for unusual signal handling patterns and ensure that setuid binaries are properly audited for similar race condition vulnerabilities.