CVE-1999-0743 in Linux
Summary
by MITRE
Trn allows local users to overwrite other users' files via symlinks.
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Analysis
by VulDB Data Team • 04/19/2026
The vulnerability identified as CVE-1999-0743 affects the trn application, a news reader software that was widely used in unix environments during the late 1990s. This flaw represents a classic file system permission and symlink manipulation issue that allowed local users to exploit the application's handling of symbolic links to overwrite files belonging to other users on the same system. The vulnerability stems from insufficient validation of file operations within the trn application, particularly when processing symbolic links that point to critical system files or user data. This issue falls under the broader category of privilege escalation and unauthorized file modification vulnerabilities.
The technical implementation of this vulnerability involves the trn application's failure to properly resolve and validate symbolic links before performing file operations. When a local user creates a symbolic link pointing to another user's file and then executes trn with specific parameters that trigger file processing, the application follows the symlink and modifies the target file instead of the intended symbolic link. This behavior creates a path traversal scenario where the application does not adequately distinguish between legitimate symbolic links and maliciously crafted ones. The vulnerability is particularly dangerous because it operates at the local user level, meaning that any user with access to the system can exploit this weakness to gain unauthorized access to other users' files. This issue is classified under CWE-59 as improper link resolution, which is a well-documented weakness in file system security.
The operational impact of CVE-1999-0743 extends beyond simple file corruption or modification, as it represents a fundamental breach in system security that could lead to data theft, service disruption, or further escalation attacks. An attacker could potentially overwrite critical system files, configuration data, or user documents with malicious content, leading to complete system compromise or data loss. The vulnerability also demonstrates poor security practices in the application's design, where input validation and file access controls were insufficiently implemented. From an attack perspective, this vulnerability aligns with ATT&CK technique T1059.007 for executing commands through Unix shell and T1078.004 for legitimate credentials, as it allows for unauthorized file modification through legitimate system utilities.
Mitigation strategies for this vulnerability should focus on both immediate system-level protections and long-term architectural improvements. System administrators should implement proper file permissions and access controls to limit the impact of such vulnerabilities, ensuring that symbolic links are properly validated before processing. The trn application should be updated to include proper symlink resolution checks and file access validation mechanisms. Additionally, implementing mandatory access controls and regular security audits can help identify similar issues in other applications. The vulnerability also highlights the importance of secure coding practices, particularly in handling file system operations and symbolic link resolution, which should be addressed through comprehensive security training for developers and adherence to secure programming guidelines. Organizations should also consider implementing file integrity monitoring systems to detect unauthorized modifications to critical files and user data.