CVE-2000-0668 in pam_console
Summary
by MITRE
pam_console PAM module in Linux systems allows a user to access the system console and reboot the system when a display manager such as gdm or kdm has XDMCP enabled.
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Analysis
by VulDB Data Team • 12/09/2024
The vulnerability described in CVE-2000-0668 represents a critical privilege escalation flaw within the pam_console pluggable authentication module on Linux systems. This issue specifically affects environments where display managers such as gdm or kdm are configured with XDMCP (X Display Manager Control Protocol) enabled, creating a dangerous intersection between authentication mechanisms and system console access. The pam_console module was designed to provide console access to users during authentication processes, but this implementation contained a fundamental security flaw that allowed unauthorized users to gain elevated privileges.
The technical flaw stems from insufficient access controls and privilege validation within the pam_console module's interaction with XDMCP-enabled display managers. When XDMCP is active, the module fails to properly verify that the requesting user has legitimate authorization to access system console functions. This oversight creates an attack vector where any authenticated user can potentially invoke console access and execute system reboot operations. The vulnerability operates at the authentication module level, bypassing normal privilege boundaries that should prevent non-privileged users from accessing critical system functions. This type of flaw aligns with CWE-284, which describes improper access control vulnerabilities where insufficient checks allow unauthorized access to protected resources.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it provides attackers with the ability to disrupt system availability through unauthorized reboot operations. An attacker who successfully exploits this vulnerability can effectively cause denial of service conditions by rebooting the system at will, potentially disrupting critical services and data availability. The attack scenario becomes particularly concerning in multi-user environments where display managers are commonly used, as it allows any authenticated user to potentially gain root-level access to console functions. This vulnerability essentially undermines the fundamental security model of Unix-like systems by allowing users to bypass traditional privilege separation mechanisms that normally prevent access to system-level functions.
Mitigation strategies for this vulnerability require immediate implementation of several security controls. The primary recommendation involves disabling XDMCP functionality on display managers when it is not strictly required, as this eliminates the attack surface entirely. System administrators should also ensure that pam_console module configurations properly validate user privileges and implement additional access controls before granting console access. Regular security audits should verify that display manager configurations do not inadvertently expose console functionality to unauthorized users. Organizations should implement principle of least privilege principles and regularly review authentication module configurations to prevent similar issues. This vulnerability demonstrates the importance of proper privilege validation in authentication modules and aligns with ATT&CK technique T1068, which covers privilege escalation through local system exploitation. The security implications extend to maintaining system integrity and availability, as unauthorized reboot capabilities can be leveraged for both disruptive attacks and potential data corruption scenarios.