CVE-2001-0872 in OpenSSH
Summary
by MITRE
OpenSSH 3.0.1 and earlier with UseLogin enabled does not properly cleanse critical environment variables such as LD_PRELOAD, which allows local users to gain root privileges.
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Analysis
by VulDB Data Team • 12/26/2024
The vulnerability described in CVE-2001-0872 represents a critical privilege escalation flaw in OpenSSH versions 3.0.1 and earlier when the UseLogin configuration option is enabled. This issue stems from insufficient sanitization of environment variables during the login process, creating a pathway for local attackers to elevate their privileges to root level access. The flaw specifically targets the LD_PRELOAD environment variable, which is commonly used to preload shared libraries in Unix-like systems, making it a prime target for exploitation.
The technical mechanism behind this vulnerability involves the improper handling of environment variables within the SSH daemon's login process. When UseLogin is enabled, OpenSSH creates a login session that should properly isolate and sanitize environment variables to prevent malicious interference. However, the implementation failed to cleanse critical variables including LD_PRELOAD, which can be manipulated by attackers to inject malicious code into the privileged login process. This occurs because the system does not adequately filter or remove potentially dangerous environment variables before executing privileged operations.
From an operational impact perspective, this vulnerability presents a severe security risk as it allows local users to bypass normal access controls and gain root privileges without requiring authentication. The exploitation process typically involves crafting a malicious shared library that gets loaded through LD_PRELOAD, which then executes arbitrary code with elevated privileges. This represents a classic privilege escalation vector that can be leveraged to establish persistent access, compromise system integrity, and potentially exfiltrate sensitive data. The vulnerability affects systems where OpenSSH is configured with UseLogin enabled, which was common in many enterprise environments during that time period.
The flaw aligns with CWE-22, which describes improper limitation of a pathname to a restricted directory, and CWE-78, which addresses improper neutralization of special elements used in OS commands. Additionally, this vulnerability maps to ATT&CK technique T1068, which covers "Exploitation for Privilege Escalation" and T1548.001, which covers "Abuse Elevation Control Mechanism." The attack surface is particularly concerning because it requires minimal privileges to exploit and can be automated, making it attractive to both malicious actors and security researchers. Organizations should prioritize immediate patching of affected OpenSSH versions, disable UseLogin if not required, and implement proper environment variable sanitization practices to prevent similar vulnerabilities from being exploited.
Mitigation strategies should include upgrading to OpenSSH versions 3.0.2 or later where this vulnerability has been addressed, disabling the UseLogin option in SSH configuration files when possible, and implementing comprehensive environment variable filtering mechanisms. System administrators should also consider implementing additional security controls such as mandatory access controls, privilege separation mechanisms, and regular security auditing to detect potential exploitation attempts. The vulnerability demonstrates the critical importance of proper environment variable handling in privileged processes and serves as a reminder of the need for thorough security testing of authentication and authorization mechanisms in network services.