Source: cve@mitre.org
CWD ~root command in ftpd allows root access.
This is a critical vulnerability in legacy FTP servers that allows attackers to gain root access. By exploiting a flaw in the CWD command, attackers can bypass authentication and execute commands with elevated privileges, potentially leading to complete system compromise. This vulnerability is extremely old and should be considered a high-priority remediation target.
Step 1: Connection Establishment: The attacker establishes an FTP connection to the vulnerable server.
Step 2: Authentication Bypass (Likely): The attacker may or may not need to authenticate. The vulnerability often allows access without valid credentials.
Step 3: Command Injection: The attacker sends the CWD ~root command to the FTP server.
Step 4: Directory Traversal: The FTP server, due to a flaw in its directory handling logic, interprets ~root as the root user's home directory.
Step 5: Access Granted: The attacker is granted access to the root user's home directory, effectively gaining root access.
The vulnerability lies in the improper handling of the CWD (Change Working Directory) command in vulnerable FTP daemons. Specifically, the server fails to adequately sanitize or validate the input provided after the CWD command, particularly when the target directory is ~root. This allows an attacker to specify a directory that, when combined with the server's internal directory resolution, results in the attacker gaining access to the root user's home directory. This is often due to a lack of proper input validation and authorization checks, allowing the attacker to bypass authentication and gain unauthorized access to sensitive system resources. The root cause is a logic error in the FTP server's command processing logic, specifically the handling of the CWD command and the subsequent directory traversal. The server incorrectly interprets the ~root directory, failing to prevent the attacker from accessing the root user's home directory.
While no specific APT groups are exclusively known for exploiting this specific CVE, it is a common attack vector used by various threat actors to gain initial access and escalate privileges on vulnerable systems. This vulnerability is often used in conjunction with other exploits. Not listed on CISA KEV, but its age and impact make it a high-risk target.
Monitor FTP server logs for suspicious CWD commands, especially those targeting ~root or other unusual directory paths.
Analyze network traffic for FTP sessions containing the CWD ~root command.
Implement file integrity monitoring to detect unauthorized changes to critical system files within the root user's home directory.
Use intrusion detection systems (IDS) with signatures specifically designed to detect this exploit.
Patching: The primary remediation is to update the FTP server software to a patched version that addresses the vulnerability. This is the most effective solution.
Disable FTP: If FTP is not required, disable the FTP service altogether. This eliminates the attack surface.
Implement Strong Authentication: Enforce strong passwords and multi-factor authentication (MFA) for FTP accounts, even if FTP is still required.
Network Segmentation: Isolate the FTP server from other critical network segments to limit the impact of a successful exploit.
Regular Security Audits: Conduct regular security audits and penetration testing to identify and address vulnerabilities.
File Integrity Monitoring: Implement file integrity monitoring to detect unauthorized changes to critical system files.