CVE-2002-0795 in FreeBSD
Summary
by MITRE
The rc system startup script for FreeBSD 4 through 4.5 allows local users to delete arbitrary files via a symlink attack on X Windows lock files.
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Analysis
by VulDB Data Team • 09/06/2019
The vulnerability identified as CVE-2002-0795 resides within the rc system startup script implementation of FreeBSD versions 4 through 4.5, representing a classic symlink attack scenario that exploits improper file handling during X Windows lock file management. This weakness fundamentally stems from insufficient validation of symbolic link references when creating or managing lock files, allowing local attackers with minimal privileges to manipulate the system's file structure through carefully crafted symlink placement. The vulnerability operates at the intersection of privilege escalation and file system manipulation, where the rc script fails to properly verify the integrity of lock file paths before attempting operations on them.
The technical flaw manifests when the rc startup script processes X Windows lock files, specifically during the initialization sequence where it creates or modifies lock file references without adequately checking whether these references point to legitimate files or symbolic links that could be manipulated by an attacker. This creates a race condition scenario where a local user can establish symbolic links with names that match those expected by the rc script, effectively redirecting file operations to arbitrary locations on the filesystem. The vulnerability is classified under CWE-59 as improper link resolution, which directly relates to the broader category of path traversal and symlink manipulation attacks. The attack vector specifically targets the startup script execution phase, making it particularly dangerous as it can potentially compromise the integrity of the entire system initialization process.
The operational impact of this vulnerability extends beyond simple file deletion capabilities, as it provides attackers with the ability to manipulate critical system files and potentially escalate privileges through strategic file replacement. Local users can leverage this weakness to delete or overwrite files in locations where the rc script has write permissions, potentially affecting system configuration files, log files, or even core system binaries if proper path validation is not implemented. The attack requires minimal privileges and can be executed without requiring network access, making it particularly concerning for systems where local access is not strictly controlled. This vulnerability aligns with ATT&CK technique T1068 which covers local privilege escalation through exploitation of system vulnerabilities, and specifically targets the system initialization process as a point of compromise.
Mitigation strategies for CVE-2002-0795 must focus on implementing proper symlink validation mechanisms within the rc startup scripts, ensuring that all file operations on lock files include comprehensive path verification and atomic file creation procedures. System administrators should immediately upgrade to FreeBSD versions beyond 4.5 where this vulnerability has been addressed through improved file handling routines and proper symlink resolution checks. The implementation of proper file permission controls and the use of atomic file operations during lock file creation can significantly reduce the attack surface. Additionally, monitoring for unauthorized symlink creation in critical system directories and implementing proper access controls for startup scripts can serve as additional defensive measures. Organizations should also consider implementing the principle of least privilege for system startup processes and regularly audit system initialization scripts for similar vulnerabilities that could be exploited through symlink attacks or other file manipulation techniques.