In late 2022, security researchers uncovered a dangerous vulnerability in the Tenda AC18 wireless router, specifically in firmware version V15.03.05.19. Tracked as CVE-2022-44176, this bug is a buffer overflow in the router’s web management interface—exploitable via the fromSetRouteStatic function. If you use a Tenda AC18, this is a serious risk that could let hackers execute code or crash your device remotely.

In this exclusive long-read, we’ll explain how this vulnerability works, break down the code, and provide references and exploit details in plain American English.

What Is a Buffer Overflow?

A buffer overflow happens when a program writes more data to a buffer than it can hold. This extra data spills over into nearby memory, which can corrupt data, crash the program, or—worse—let hackers run their own code.

Where Exactly Is the Problem?

The vulnerability exists in Tenda’s AC18 router web interface, inside the handler function for changing or adding static routes:

Firmware Version: V15.03.05.19

- Endpoint/Handler: fromSetRouteStatic
- CVE Reference: CVE-2022-44176 on NVD

This function does not properly check user input. If someone sends a specially crafted HTTP POST request with too much data, it overflows the buffer in memory.

Step-by-Step Vulnerability Breakdown

1. User Sends Data: The router receives configuration changes through HTTP POST, in particular to the /goform/SetRouteStatic endpoint.
 
2. Parsing User Input: The handler fromSetRouteStatic parses fields like IP address, subnet mask, gateway, and device name—but it does not enforce length limits for some fields.

3. Buffer Overflow: If a malicious actor sends a very long string in one of these fields, the data exceeds buffer size and overwrites adjacent memory.

4. Attackers Take Control: With careful crafting, an attacker can overwrite crucial data—like function pointers or return addresses—leading to remote code execution.

The Vulnerable Code

Although Tenda doesn’t publish their source code, researchers have reverse-engineered the firmware and published snippets. Here’s a simplified pseudo-code to illustrate what’s happening:

void fromSetRouteStatic(request) {
    char gateway[16];
    char netdev[32];
    // ... other variables ...

    // Get parameters from HTTP request
    // (No checks on input lengths)
    strcpy(gateway, request->getParam("gateway"));
    strcpy(netdev, request->getParam("netdev"));
    // ... process route ...
}

What's the problem?
Functions like strcpy are dangerous—they copy data with no length checks. If someone sends a big string for "netdev", it will overflow the netdev buffer.

Proof-of-Concept (PoC)

import requests

url = 'http://<ROUTER_IP>/goform/SetRouteStatic';
data = {
    'gateway': '192.168.1.1',
    'netdev': 'A' * 100,  # Overlong string triggers overflow
    'other_param': 'value'
}

resp = requests.post(url, data=data)
print(resp.text)

If the router processes this, it may crash, reboot, or—in more sophisticated attacks—execute malicious instructions.

What Should You Do?

1. Update Firmware: Tenda may release a patched firmware—check their support page.

References

- CVE-2022-44176 (NIST NVD)
- Exploit Database Entry
- Chinese Security Writeup
- Firmware Download (Tenda)

Conclusion

CVE-2022-44176 is a serious buffer overflow in Tenda AC18 routers (V15.03.05.19) that allows attackers on the network (and possibly beyond) to gain complete control. The root cause is a lack of input validation in the vulnerable fromSetRouteStatic function.

If you own a Tenda AC18, act now—lock down your network and look for firmware updates. Stay safe!


*Exclusive insight by ChatGPT. For educational purposes only—don’t attack systems without permission.*

Timeline

Published on: 11/21/2022 18:15:00 UTC
Last modified on: 11/28/2022 13:47:00 UTC