CVE-2000-0312 in OpenBSD
Summary
by MITRE
cron in OpenBSD 2.5 allows local users to gain root privileges via an argv[] that is not NULL terminated, which is passed to cron s fake popen function.
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Analysis
by VulDB Data Team • 05/29/2018
The vulnerability identified as CVE-2000-0312 represents a critical privilege escalation flaw within the cron daemon implementation of OpenBSD version 2.5. This issue stems from improper handling of command-line arguments in the cron service, specifically affecting how the system processes user-provided input through the fake popen function. The flaw exists at the intersection of buffer management and privilege handling, creating a pathway for local attackers to elevate their system access from standard user level to root privileges. The vulnerability demonstrates a classic example of improper input validation and memory management that can be exploited to bypass security controls.
The technical root cause of this vulnerability lies in the cron daemon's failure to properly null-terminate command-line arguments before passing them to the internal fake popen function. When cron processes scheduled tasks, it accepts user-provided command arguments through the argv array structure. In the affected OpenBSD 2.5 implementation, the cron service does not ensure that the argv array is properly null-terminated before invoking the fake popen function. This oversight creates a buffer overflow condition that allows malicious input to overwrite adjacent memory locations, potentially corrupting the program execution flow. The vulnerability specifically targets the argv[] array handling within the cron daemon's argument processing routine, which is part of the broader category of buffer overflow vulnerabilities classified under CWE-121. The improper null termination enables attackers to craft malicious command-line arguments that can manipulate the execution environment and exploit the memory corruption to gain elevated privileges.
The operational impact of CVE-2000-0312 is severe and directly affects system integrity and security posture. Local users who can execute commands on the target system can leverage this vulnerability to escalate their privileges to root level, effectively compromising the entire system. Once an attacker gains root access through this method, they can manipulate system files, install persistent backdoors, modify security configurations, and access all user data on the system. The attack vector requires only local system access, making it particularly dangerous as it can be exploited by any user with login privileges. This vulnerability aligns with ATT&CK technique T1068 which describes privilege escalation through local exploits, and represents a fundamental failure in the principle of least privilege enforcement within the operating system's privilege management system. The exploitation of this vulnerability can lead to complete system compromise and is classified as a high-severity issue according to industry security standards.
Mitigation strategies for CVE-2000-0312 must address both immediate remediation and long-term security hardening measures. The primary solution involves updating to a patched version of OpenBSD that properly handles argv array null termination in the cron daemon implementation. System administrators should immediately apply the relevant security patches released by OpenBSD to prevent exploitation of this vulnerability. Additionally, implementing proper input validation and bounds checking in all system components can prevent similar issues from occurring in the future. Security hardening measures should include restricting cron access to authorized users only, implementing proper file permissions for cron-related files, and monitoring for suspicious cron job activities. Organizations should also consider implementing intrusion detection systems to monitor for exploitation attempts and maintain regular security audits to identify potential vulnerabilities in system components. The vulnerability serves as a reminder of the critical importance of proper memory management and input validation in security-sensitive applications, particularly those with elevated privilege requirements, and demonstrates the necessity of following secure coding practices as outlined in the CWE guidelines for preventing buffer overflow conditions.