CVE-2001-0685 in Fcron
Summary
by MITRE
Thibault Godouet FCron prior to 1.1.1 allows a local user to corrupt another user s crontab file via a symlink attack on the fcrontab temporary file.
If you want to get the best quality for vulnerability data then you always have to consider VulDB.
Analysis
by VulDB Data Team • 01/19/2025
The vulnerability described in CVE-2001-0685 affects FCron versions prior to 1.1.1, specifically targeting the way the system handles temporary files during crontab operations. This issue represents a classic symlink attack scenario where a local malicious user can exploit improper file handling to manipulate another user's crontab file. The vulnerability resides in the temporary file creation process where FCron does not properly validate or secure temporary file paths, creating an opportunity for privilege escalation and unauthorized system modification.
The technical flaw manifests through a race condition in the temporary file handling mechanism. When FCron processes crontab commands, it creates temporary files that are subsequently moved or renamed to their final destination. An attacker can create a symbolic link in the temporary file path that points to another user's crontab file before the legitimate file operations complete. This allows the attacker to write arbitrary content into the target user's crontab, potentially executing malicious commands with the privileges of that user. The vulnerability is classified under CWE-367 which specifically addresses Time-of-Check to Time-of-Use (TOCTOU) race conditions, making it a well-documented pattern of insecure temporary file handling.
The operational impact of this vulnerability extends beyond simple privilege escalation as it can enable persistent access and privilege abuse across multiple user accounts. When an attacker successfully corrupts another user's crontab, they can establish backdoors, schedule malicious activities, or maintain unauthorized access to systems. This type of vulnerability is particularly dangerous in multi-user environments where different users may have varying privilege levels. The attack vector is relatively simple to execute and does not require network connectivity, making it an attractive target for attackers seeking to maintain access or escalate privileges on compromised systems.
Mitigation strategies for this vulnerability primarily focus on implementing proper temporary file handling practices and adopting security measures aligned with the ATT&CK framework's privilege escalation techniques. System administrators should immediately upgrade to FCron version 1.1.1 or later where this vulnerability has been patched. Additionally, implementing proper file permissions and ensuring that temporary files are created with secure umask settings can prevent similar issues. The vulnerability demonstrates the importance of following secure coding practices such as using secure temporary file creation functions and avoiding predictable temporary file names. Organizations should also implement monitoring for unauthorized crontab modifications and establish proper user access controls to limit potential damage from such attacks. Regular security audits of system utilities and proper implementation of the principle of least privilege can significantly reduce the risk exposure from this type of vulnerability.