CVE-2005-1993 in sudo
Summary
by MITRE
Race condition in sudo 1.3.1 up to 1.6.8p8, when the ALL pseudo-command is used after a user entry in the sudoers file, allows local users to gain privileges via a symlink attack.
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Analysis
by VulDB Data Team • 07/05/2021
The vulnerability described in CVE-2005-1993 represents a critical race condition flaw in the sudo privilege escalation mechanism that affected versions 1.3.1 through 1.6.8p8. This issue arises specifically when the ALL pseudo-command is utilized in sudoers file configurations, creating a window of opportunity for malicious local users to exploit the system's privilege management. The race condition occurs during the processing of sudo commands where the system fails to properly validate file access permissions at critical moments, allowing attackers to manipulate the environment and escalate their privileges.
The technical implementation of this vulnerability stems from how sudo handles file operations when processing user entries with the ALL pseudo-command. When a user with specific sudoers permissions attempts to execute commands, the system creates temporary files or directories that can be manipulated through symbolic link attacks. The race condition manifests when the sudo process checks for file existence or permissions before actually accessing the file, but between these checks and the actual file access, an attacker can replace the targeted file with a symbolic link pointing to a privileged file. This timing window enables unauthorized access to system resources that should otherwise be restricted to privileged users.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it fundamentally undermines the security model that sudo is designed to enforce. Local attackers can leverage this flaw to bypass the intended access controls and potentially gain root privileges on affected systems. The attack vector is particularly dangerous because it requires minimal privileges to initiate and can be executed by any local user who has been granted specific sudo permissions. This vulnerability affects systems where the ALL pseudo-command is used in sudoers configurations, making it a widespread concern across Unix-like systems that implement sudo for privilege management.
The vulnerability aligns with CWE-367, which identifies the weakness of Time-of-Check to Time-of-Use (TOCTOU) race conditions as a critical security flaw. This classification emphasizes the fundamental issue of inconsistent state validation between security checks and actual operations. From an ATT&CK framework perspective, this vulnerability maps to privilege escalation techniques using local exploitation methods, specifically targeting the T1068 privilege escalation sub-technique. The attack requires the adversary to have local access to the system and knowledge of the sudoers configuration, but once exploited, it provides a persistent path to elevated privileges that can be used for further system compromise.
Mitigation strategies for this vulnerability include immediate patching of sudo versions to 1.6.9p1 or later, where the race condition has been addressed through improved file access validation. System administrators should also review sudoers configurations to minimize the use of the ALL pseudo-command and implement more granular permissions. Additional protective measures include disabling unnecessary sudo privileges, implementing proper file system permissions, and monitoring for suspicious symlink creation patterns. The vulnerability serves as a reminder of the critical importance of proper synchronization and validation in privilege management systems, where even small timing gaps can lead to significant security breaches. Organizations should conduct comprehensive audits of their sudo configurations and ensure that all systems are updated to patched versions to prevent exploitation of this race condition.