Source: cve@mitre.org
FormMail CGI program allows remote execution of commands.
FormMail, a common CGI script, is vulnerable to remote command execution, allowing attackers to execute arbitrary commands on the server. This vulnerability, dating back to the late 90s, presents a significant risk of system compromise and data breaches if unpatched and exposed. Exploitation can lead to full control of the web server and potentially the entire network.
Step 1: Identify Target: The attacker identifies a web server running FormMail.cgi.
Step 2: Craft Payload: The attacker crafts a malicious payload, typically a command injection string, designed to execute commands on the server. This payload is often embedded within a form field.
Step 3: Payload Delivery: The attacker submits a specially crafted form to the FormMail.cgi script, including the malicious payload in a vulnerable form field (e.g., the 'recipient' or 'redirect' field).
Step 4: Command Execution: The FormMail.cgi script, due to insufficient input validation, processes the attacker's input and executes the injected commands on the server's operating system.
Step 5: Result Retrieval (Optional): The attacker might use the executed commands to retrieve information (e.g., /etc/passwd) or establish a reverse shell for persistent access.
The vulnerability stems from insufficient input validation within the FormMail CGI script. Specifically, the script often processes user-supplied data, such as form field values, without proper sanitization. Attackers can inject malicious commands into these fields, which are then executed by the server's operating system. The lack of secure coding practices, such as proper escaping and filtering of user input, allows for the execution of arbitrary code. The root cause is a failure to restrict the execution of commands based on user-supplied data, leading to a command injection vulnerability.
This vulnerability is a favorite of opportunistic attackers and could be leveraged by various threat actors. While not directly linked to specific APTs, the ease of exploitation makes it a common target. CISA KEV status: Not Listed (due to age and likely widespread patching, but the risk remains if unpatched).
Web server logs: Examine access logs for suspicious POST requests to FormMail.cgi with unusual parameters or command injection attempts (e.g., using shell metacharacters like ';', '|', '&', or backticks).
Intrusion Detection Systems (IDS): Implement rules to detect known FormMail exploit patterns and command injection attempts.
File Integrity Monitoring (FIM): Monitor the FormMail.cgi file for unauthorized modifications.
Network traffic analysis: Analyze network traffic for unusual outbound connections from the web server, which could indicate a reverse shell or data exfiltration.
Patching: The primary remediation is to update or remove the vulnerable FormMail.cgi script. If a patched version is available, apply it immediately.
Removal: If FormMail is not essential, remove it from the server to eliminate the attack surface.
Input Validation: Implement robust input validation and sanitization for all user-supplied data. This includes escaping special characters and filtering potentially malicious input.
Web Application Firewall (WAF): Deploy a WAF to filter malicious requests and block known exploit attempts.
Least Privilege: Ensure the web server process runs with the least privileges necessary to perform its functions. This limits the impact of a successful exploit.
Regular Security Audits: Conduct regular security audits and penetration testing to identify and address vulnerabilities.