CVE-2000-0816 in Linux
Summary
by MITRE
Linux tmpwatch --fuser option allows local users to execute arbitrary commands by creating files whose names contain shell metacharacters.
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Analysis
by VulDB Data Team • 12/02/2024
The vulnerability described in CVE-2000-0816 represents a critical command injection flaw within the Linux tmpwatch utility that operates under the Common Weakness Enumeration category of CWE-78 and aligns with ATT&CK technique T1059.001 for executing malicious commands through shell injection. This vulnerability specifically affects the --fuser option of tmpwatch, which is designed to identify and remove files that have not been accessed for a specified period. The flaw occurs when tmpwatch processes file names containing shell metacharacters, allowing local attackers to inject arbitrary commands through carefully crafted filenames. The tmpwatch utility is commonly used in system administration tasks to clean up temporary files, particularly in environments where automated cleanup processes are essential for maintaining system performance and security.
The technical implementation of this vulnerability stems from improper input validation and sanitization within the tmpwatch utility's handling of file names. When the --fuser option is invoked, the utility executes system calls that process file names without adequate shell escaping or command separation mechanisms. Attackers can exploit this by creating specially named files that contain shell metacharacters such as semicolons, pipes, or backticks, which are then interpreted by the shell when tmpwatch processes these filenames. This type of vulnerability falls under the broader category of command injection attacks where user-controllable input is directly incorporated into shell commands without proper sanitization. The vulnerability demonstrates a classic lack of proper input validation that has been documented in numerous security frameworks and standards, including the OWASP Top 10 and NIST cybersecurity guidelines for secure coding practices.
The operational impact of this vulnerability is significant for Linux systems that rely on tmpwatch for automated file cleanup operations, particularly in multi-user environments where local privilege escalation is a concern. An attacker with local access can potentially execute arbitrary commands with the privileges of the user running tmpwatch, which may include root privileges in some configurations. This creates a pathway for privilege escalation attacks that can lead to complete system compromise. The vulnerability is particularly dangerous because it operates at the system level and can be exploited through normal file creation operations, making detection difficult. The attack vector is straightforward and requires minimal technical expertise, as demonstrated by the widespread exploitation patterns observed in security incident reports. The vulnerability affects systems where tmpwatch is regularly executed with elevated privileges, either through cron jobs or system-level automation scripts.
Mitigation strategies for CVE-2000-0816 must address both immediate remediation and long-term architectural improvements. The most effective immediate solution involves patching the tmpwatch utility to properly sanitize input parameters and escape shell metacharacters before processing file names. Organizations should implement proper file name validation that rejects or sanitizes special characters that could be interpreted by the shell. System administrators should review and restrict the execution permissions of tmpwatch, particularly when running with elevated privileges, and consider implementing alternative cleanup mechanisms that do not rely on shell command execution. The vulnerability highlights the importance of following secure coding practices as outlined in ISO/IEC 27034 and NIST SP 800-163 guidelines, which emphasize the need for input validation, output encoding, and proper privilege management. Additionally, implementing monitoring systems to detect unusual file creation patterns and shell command execution can help identify exploitation attempts. Organizations should also consider implementing principle of least privilege models, ensuring that system utilities run with minimal necessary permissions to limit the potential impact of such vulnerabilities. The remediation process should include comprehensive testing of patched versions to ensure that legitimate functionality is preserved while eliminating the security flaw.