CVE-2004-0559 in Webmin
Summary
by MITRE
The maketemp.pl script in Usermin 1.070 and 1.080 allows local users to overwrite arbitrary files at install time via a symlink attack on the /tmp/.usermin directory.
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Analysis
by VulDB Data Team • 07/19/2019
The vulnerability identified as CVE-2004-0559 represents a critical privilege escalation flaw in Usermin versions 1.070 and 1.080 that stems from improper handling of temporary directories during the installation process. This issue specifically affects the maketemp.pl script which is responsible for creating temporary files and directories required for Usermin's operational setup. The flaw manifests when the installation script creates a temporary directory at /tmp/.usermin without adequate security measures to prevent symbolic link attacks, creating a window of opportunity for local attackers to manipulate the installation process.
The technical implementation of this vulnerability aligns with CWE-367, which addresses Time-of-Check to Time-of-Use (TOCTOU) race conditions that occur when a system checks a resource's properties and then uses that resource in a way that could allow an attacker to modify the resource between the check and use operations. In this case, the installation script performs a directory check and creation operation that can be exploited through a symbolic link attack. Attackers can create a symbolic link at /tmp/.usermin pointing to a target file they wish to overwrite, and when the maketemp.pl script executes with elevated privileges during installation, it will create the directory structure that overwrites the target file instead of creating the intended temporary directory.
The operational impact of this vulnerability extends beyond simple file overwriting capabilities as it enables local users to potentially modify critical system files, configuration data, or even executable components that could lead to persistent access or privilege escalation. When the installation process runs with root privileges, the attacker gains the ability to overwrite files with elevated permissions, potentially compromising the integrity of the entire system. This vulnerability particularly affects Unix-based systems where Usermin is commonly deployed, and the exploitation can occur during any installation or upgrade process where the temporary directory creation logic is executed.
The attack vector for this vulnerability requires local system access and involves the attacker creating a symbolic link before the installation process begins. This type of attack pattern is categorized under ATT&CK technique T1059.001 for command and scripting interpreter and T1068 for exploit for privilege escalation. The exploitation process typically involves creating a symbolic link from /tmp/.usermin to a system file such as /etc/passwd or another critical configuration file, then executing the installation script which will overwrite the target file with the contents of the temporary directory structure. Security practitioners should note that this vulnerability demonstrates the importance of proper temporary file handling and the principle of least privilege in system administration tools. The recommended mitigations include immediate patching of affected Usermin versions, implementing proper directory creation with secure permissions, and ensuring that installation processes validate the existence and integrity of temporary directories before creating them. Organizations should also consider implementing file system monitoring and access controls to detect and prevent unauthorized symbolic link creation in temporary directories.