CVE-2000-0890 in FreeBSD
Summary
by MITRE
periodic in FreeBSD 4.1.1 and earlier, and possibly other operating systems, allows local users to overwrite arbitrary files via a symlink attack.
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Analysis
by VulDB Data Team • 12/26/2024
The vulnerability described in CVE-2000-0890 represents a significant security flaw in the periodic utility across FreeBSD versions 4.1.1 and earlier, with potential impacts extending to other operating systems. This issue arises from improper handling of symbolic links during file operations, creating a path traversal scenario that enables local attackers to manipulate the file system in unintended ways. The periodic utility is designed to execute scheduled tasks and system maintenance routines, making it a critical component that requires robust security controls to prevent unauthorized modifications.
The technical implementation of this vulnerability stems from the way periodic processes handle file creation and modification operations when symbolic links are present in the target directory structure. When periodic executes scripts or creates temporary files, it fails to properly validate the symbolic link targets, allowing an attacker to establish a malicious symlink that points to a system-critical file. This flaw operates under CWE-59, which specifically addresses improper handling of symbolic links, and represents a classic case of symlink-based privilege escalation. The vulnerability is particularly concerning because it allows local users to overwrite files that they would normally not have write permissions to modify, effectively bypassing normal access controls and file system protections.
The operational impact of this vulnerability extends beyond simple file overwrites, as it provides attackers with a mechanism to modify critical system files, configuration data, or even binaries that are executed by the periodic utility itself. Attackers can exploit this weakness to inject malicious code into system processes, potentially escalating their privileges to root level access. The vulnerability is particularly dangerous in multi-user environments where local users might have limited access to system resources but can manipulate the periodic execution framework to gain broader system control. This type of attack aligns with ATT&CK technique T1059.007 for execution through scheduled tasks and T1543.003 for persistence through scheduled tasks, making it a vector for both privilege escalation and system compromise.
Mitigation strategies for CVE-2000-0890 require immediate system updates to patched versions of FreeBSD and other affected operating systems, as the vulnerability has been addressed through proper symbolic link validation in subsequent releases. System administrators should also implement restrictive file permissions on directories used by periodic utilities, ensuring that no user has write access to critical system paths that periodic might traverse. Additional protective measures include monitoring for unauthorized symbolic link creation in system directories and implementing mandatory access controls through mechanisms such as SELinux or similar security frameworks. The vulnerability demonstrates the importance of proper input validation and the need for security-conscious development practices, particularly when handling file system operations that involve user-controlled paths or symbolic links. Organizations should also consider implementing file integrity monitoring solutions to detect unauthorized modifications to critical system files that could result from exploitation of this vulnerability.