CVE-2009-0360 in pam-krb5
Summary
by MITRE
Russ Allbery pam-krb5 before 3.13, when linked against MIT Kerberos, does not properly initialize the Kerberos libraries for setuid use, which allows local users to gain privileges by pointing an environment variable to a modified Kerberos configuration file, and then launching a PAM-based setuid application.
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Analysis
by VulDB Data Team • 12/21/2024
The vulnerability identified as CVE-2009-0360 affects the pam-krb5 module version 3.12 and earlier, which serves as a Pluggable Authentication Module for integrating Kerberos authentication into Linux systems. This issue specifically manifests when pam-krb5 is linked against the MIT Kerberos library implementation, creating a critical privilege escalation vector for local attackers. The flaw stems from improper initialization of Kerberos library components during setuid application execution, fundamentally undermining the security model that protects privileged operations from malicious environment manipulation.
The technical root cause of this vulnerability lies in the insufficient initialization of Kerberos library state when pam-krb5 operates within setuid contexts. When a PAM-based setuid application launches, the Kerberos libraries must be properly configured to handle the elevated privilege environment. However, pam-krb5 versions prior to 3.13 fail to initialize these libraries correctly, allowing attackers to manipulate environment variables such as KRB5_CONFIG to point to maliciously crafted Kerberos configuration files. This misconfiguration creates a path where local users can inject arbitrary Kerberos settings that persist through the setuid execution context, effectively bypassing the security boundaries that should prevent privilege escalation.
The operational impact of this vulnerability extends beyond simple local privilege escalation, as it represents a fundamental breakdown in the security model of setuid applications. Attackers can leverage this flaw to execute arbitrary code with elevated privileges, potentially gaining access to sensitive system resources, modifying critical system files, or establishing persistent backdoors. The vulnerability is particularly concerning because it operates silently within the normal operation of legitimate setuid applications, making detection difficult and exploitation straightforward for attackers familiar with Kerberos internals. This issue affects systems where pam-krb5 is configured as part of the authentication stack for applications requiring Kerberos authentication, commonly found in enterprise environments with centralized authentication systems.
Mitigation strategies for this vulnerability require immediate patching of pam-krb5 to version 3.13 or later, which implements proper Kerberos library initialization for setuid contexts. System administrators should also implement strict environment variable controls and monitoring for unauthorized Kerberos configuration file modifications. The vulnerability aligns with CWE-276, which addresses improper privilege management, and maps to ATT&CK technique T1068, privilege escalation through environment variable manipulation. Organizations should conduct comprehensive vulnerability assessments to identify systems running affected pam-krb5 versions and implement configuration management controls to prevent unauthorized modifications to Kerberos configuration files. Additionally, regular security audits should verify that setuid applications properly initialize security libraries and that environment variable handling follows secure coding practices to prevent similar vulnerabilities from emerging in other components of the authentication stack.