CVE-1999-0123 in Linux
Summary
by MITRE
race condition in linux mailx command allows local users to read user files.
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Analysis
by VulDB Data Team • 04/03/2025
The vulnerability identified as CVE-1999-0123 represents a classic race condition flaw in the linux mailx command that fundamentally undermines file access controls and system security. This issue manifests when the mailx utility creates temporary files during its operation, creating a window of opportunity for malicious local users to exploit the timing gap between file creation and access control enforcement. The race condition occurs specifically during the process of handling mail delivery where the system generates temporary files that are initially created with permissive permissions before proper access controls are applied. This temporal vulnerability allows attackers to intercept or manipulate these temporary files before they are properly secured, potentially enabling unauthorized access to sensitive user data.
The technical implementation of this race condition stems from improper file handling procedures within the mailx utility where temporary files are created without adequate synchronization mechanisms. When the mailx command processes mail operations, it typically creates temporary files in predictable locations with default permissions that may be accessible to other users on the system. The flaw arises because the application does not properly implement atomic operations or sufficient locking mechanisms to prevent concurrent access during the file creation phase. This vulnerability directly maps to CWE-362, which specifically addresses race conditions in software implementations where the timing of operations creates security weaknesses. The underlying issue demonstrates poor resource management practices where file system operations lack proper atomicity guarantees, making the system susceptible to privilege escalation and information disclosure attacks.
From an operational impact perspective, this vulnerability enables local users to read files that they would normally not have access to, potentially compromising sensitive user data including personal communications, configuration files, and other private information. The attack vector is particularly concerning because it requires only local system access, making it difficult to detect and trace through network monitoring tools. An attacker could exploit this vulnerability to gain access to other users' mail files, system configuration data, or any files that the mailx utility might temporarily process. The implications extend beyond simple file access, as this could serve as a stepping stone for further attacks, potentially allowing for privilege escalation or information gathering that could be leveraged in more sophisticated attacks. The vulnerability affects the fundamental security model of the system by undermining the principle of least privilege and creating unexpected access paths.
Mitigation strategies for CVE-1999-0123 should focus on implementing proper file handling procedures that eliminate the race condition window. System administrators should ensure that all temporary files are created with restrictive permissions and that proper atomic operations are implemented to prevent concurrent access during file creation. The recommended approach involves modifying the mailx utility to use secure temporary file creation methods that prevent other users from accessing these files during their creation phase. Additionally, implementing proper file locking mechanisms and ensuring that all temporary files are properly cleaned up after use can significantly reduce the attack surface. Organizations should also consider updating to newer versions of mailx or alternative mail handling utilities that have addressed these timing issues. This vulnerability highlights the importance of following secure coding practices and adheres to ATT&CK technique T1068 which involves local privilege escalation through race conditions and improper access control implementations. The fix should also include monitoring for unauthorized file access patterns and implementing proper logging of mailx operations to detect potential exploitation attempts.