CVE-2005-0580 in cmd5checkpw
Summary
by MITRE
cmd5checkpw when running setuid does not properly drop privileges before calling the execvp function which allows local users to read the poppasswd file.
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Analysis
by VulDB Data Team • 07/01/2021
The vulnerability identified as CVE-2005-0580 affects the cmd5checkpw utility when executed with setuid privileges, representing a critical privilege escalation flaw that undermines fundamental security principles of Unix-like systems. This issue resides in the program's privilege management implementation where it fails to properly relinquish elevated privileges before invoking the execvp system call. The cmd5checkpw utility is typically used for password verification in certain mail server implementations, particularly those utilizing the courier authentication system. When the program runs with setuid root privileges, it should immediately drop these privileges to prevent unauthorized access to sensitive system resources. However, the flawed implementation allows the program to maintain elevated privileges during the execvp execution, creating a window of opportunity for local attackers to exploit this weakness.
The technical flaw manifests through improper privilege handling within the program's execution flow, where the setuid mechanism is not correctly managed before the execvp function call. This behavior creates a privilege escalation vector that directly violates the principle of least privilege, a fundamental security concept that requires programs to operate with the minimum necessary permissions. The vulnerability specifically affects systems where cmd5checkpw is installed with setuid root permissions, typically found in mail server configurations that use the courier authentication system for managing user passwords. When the program executes, it retains root privileges during the execvp call, allowing it to access files that would normally be restricted to root users. This oversight enables local users to read the poppasswd file, which contains password hashes for mail accounts and represents a significant security compromise.
The operational impact of this vulnerability extends beyond simple privilege escalation to encompass potential data leakage and unauthorized access to mail server credentials. Local attackers who can execute cmd5checkpw with setuid privileges can exploit this flaw to read the poppasswd file, which typically contains password hashes for user accounts that can be cracked using various password recovery techniques. This vulnerability affects systems where the courier mail server implementation is deployed, particularly in environments where multiple users have access to the system but should not have root-level privileges. The attack vector is straightforward since the vulnerability exists in the program's default execution path when run with setuid permissions, making it accessible to any local user who can execute the utility. The exploitation process requires minimal technical skill and can result in unauthorized access to multiple mail accounts, potentially leading to further system compromise through credential reuse attacks.
Mitigation strategies for CVE-2005-0580 should focus on immediate privilege management fixes and system hardening measures. The primary remediation involves modifying the cmd5checkpw source code to ensure proper privilege dropping before any execvp calls are made, implementing the standard security practice of dropping privileges as soon as possible after setuid execution. System administrators should also verify that the cmd5checkpw utility is not installed with unnecessary setuid permissions, as the functionality can often be achieved through alternative mechanisms that do not require root privileges. Additionally, regular security audits should be conducted to identify other setuid programs that may exhibit similar privilege management flaws, as this represents a common class of vulnerabilities that can lead to privilege escalation attacks. The vulnerability aligns with CWE-276, which addresses improper privileges, and relates to ATT&CK technique T1068, which covers privilege escalation through local exploits. Organizations should also consider implementing privilege separation mechanisms and monitoring for unauthorized access attempts to sensitive password files, as this vulnerability represents a classic example of how improper privilege handling can undermine system security.