CVE-2012-6095 in ProFTPD
Summary
by MITRE
ProFTPD before 1.3.5rc1, when using the UserOwner directive, allows local users to modify the ownership of arbitrary files via a race condition and a symlink attack on the (1) MKD or (2) XMKD commands.
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Analysis
by VulDB Data Team • 12/24/2024
The vulnerability described in CVE-2012-6095 represents a critical security flaw in ProFTPD versions prior to 1.3.5rc1 that stems from improper handling of file ownership operations within the FTP server's implementation. This issue specifically manifests when the UserOwner directive is enabled, creating a scenario where local users can exploit a race condition to manipulate file ownership across the system. The vulnerability affects the MKD and XMKD commands, which are fundamental directory creation operations within the FTP protocol. The flaw arises from the server's failure to properly validate file ownership during directory creation operations, allowing malicious users to leverage symbolic link attacks to gain unauthorized control over file permissions.
The technical execution of this vulnerability involves a classic race condition attack pattern where an attacker creates a symbolic link to a target file before the FTP server processes the directory creation command. When ProFTPD processes the MKD or XMKD command, it performs directory creation operations that can be manipulated through the symlink attack to redirect the ownership modification to arbitrary files rather than the intended target. This race condition occurs because the server does not properly synchronize access to file ownership operations or validate the integrity of file paths during directory creation. The vulnerability is particularly dangerous because it operates at the local user level, meaning that any user with access to the FTP service can potentially exploit this flaw to modify ownership of files they should not have access to. The attack vector relies on the server's failure to properly handle file system operations in a multi-threaded or concurrent environment where the symbolic link can be manipulated between the time of path resolution and actual file system modification.
From an operational impact perspective, this vulnerability compromises the fundamental security model of the FTP server by allowing unauthorized file ownership changes that can lead to privilege escalation and persistent access to system resources. The implications extend beyond simple file ownership manipulation, as attackers can potentially use this vulnerability to create backdoors, modify critical system files, or establish persistent access to the system. The vulnerability affects the integrity and confidentiality of the file system, as unauthorized users can modify file ownership to gain access to files they should not be able to access. This type of attack aligns with attack techniques documented in the MITRE ATT&CK framework under privilege escalation and persistence tactics, where attackers leverage system-level vulnerabilities to gain elevated access rights. The vulnerability also relates to CWE-367, which describes Time-of-Check to Time-of-Use (TOCTOU) flaws, where the state of a resource changes between the time it is checked and when it is used, creating opportunities for exploitation.
The mitigation strategy for this vulnerability requires immediate patching of ProFTPD installations to version 1.3.5rc1 or later, where the race condition has been addressed through proper synchronization of file ownership operations and enhanced validation of file paths during directory creation. System administrators should also implement additional security controls such as disabling the UserOwner directive when not strictly necessary, implementing proper file system permissions, and monitoring for suspicious directory creation patterns. The fix addresses the underlying race condition by ensuring that file ownership operations are atomic and that symbolic link attacks cannot be used to redirect file system operations. Organizations should also consider implementing network segmentation and access controls to limit local user access to FTP services, as this vulnerability requires local system access to exploit. Regular security audits and vulnerability assessments should be conducted to identify and remediate similar race condition vulnerabilities in other system components, particularly those involving file system operations and concurrent access patterns. The vulnerability demonstrates the importance of proper synchronization mechanisms in multi-threaded applications and the critical need for validating file system operations in security-sensitive contexts.