CVE-2001-0138 in wu-ftpd
Summary
by MITRE
privatepw program in wu-ftpd before 2.6.1-6 allows local users to overwrite arbitrary files via a symlink attack.
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Analysis
by VulDB Data Team • 05/23/2019
The vulnerability identified as CVE-2001-0138 resides within the privatepw program component of wu-ftpd versions prior to 2.6.1-6, representing a critical security flaw that enables local attackers to perform arbitrary file overwrite operations through symbolic link manipulation. This issue demonstrates a classic race condition vulnerability where the program fails to properly validate file operations, creating an exploitable window where malicious users can manipulate file system access. The privatepw utility, designed to manage password files for the wu-ftpd service, operates with elevated privileges and handles sensitive authentication data, making this vulnerability particularly dangerous for system security.
The technical implementation of this flaw involves the program's improper handling of temporary files during the password update process. When privatepw executes, it creates temporary files in predictable locations without adequate security checks to prevent symbolic link attacks. Local users can exploit this by creating symbolic links that point to critical system files or configuration data, then triggering the privatepw program to write to these locations. The vulnerability stems from the program's lack of proper file validation and atomic file operations, allowing attackers to redirect write operations to unintended targets. This type of attack falls under the category of privilege escalation through file system manipulation, where the attacker leverages the elevated privileges of the privileged program to overwrite files with malicious content.
The operational impact of CVE-2001-0138 extends beyond simple file overwrites, as it can enable attackers to modify critical system components including authentication databases, configuration files, and potentially system binaries. Attackers can leverage this vulnerability to gain persistent access to systems, escalate privileges, or disrupt services by replacing essential files with malicious counterparts. The vulnerability is particularly concerning because it requires minimal privileges to exploit, as local access is sufficient to create symbolic links and trigger the vulnerable code path. This makes it an attractive target for both casual attackers seeking to compromise systems and more sophisticated threat actors looking to establish persistent footholds within network environments.
Security practitioners should note that this vulnerability aligns with CWE-367, which describes the "Time-of-Check to Time-of-Use (TOCTOU) race condition" pattern, where the security check occurs at a different time than the actual operation, creating an exploitable window. The attack vector corresponds to ATT&CK technique T1068, which involves the exploitation of legitimate credentials and privileges for unauthorized access. Organizations should prioritize immediate patching of affected wu-ftpd installations to version 2.6.1-6 or later, as this vulnerability represents a clear path for privilege escalation and system compromise. Additionally, system administrators should implement proper file system permissions, monitor for suspicious symbolic link creation, and conduct regular security audits to identify and remediate similar vulnerabilities in other system components. The remediation process should include verifying that temporary file operations are atomic and that programs properly validate file access before executing privileged operations.