Summary:
A recent vulnerability, CVE-2024-34944, was discovered in the Tenda FH1206 router (firmware version V1.2..8(8155)_EN). The bug is a stack-based buffer overflow triggered by the list1 parameter in the /goform/DhcpListClient endpoint. In this article, we'll break down what this vulnerability is, show a proof-of-concept (PoC) exploit, and discuss the risk for users. We aim to help both beginners and seasoned researchers understand how this works.

[References](#references)

1. Background on the Tenda FH1206

Tenda's FH1206 is a popular budget home router, used worldwide. The device offers a web-based management interface, which can be accessed on a local network.

The firmware version V1.2..8(8155)_EN is the focus of this vulnerability.


2. The Vulnerability Explained

CVE-2024-34944 relates to insecure handling of the list1 HTTP POST parameter at /goform/DhcpListClient. The code handling list1 does not perform bounds checking, allowing an attacker to overflow the buffer on the stack. This can potentially lead to code execution on the device.

What does that mean in plain English? If someone on your network sends a specially crafted request to the router, they could take control of it or crash it.


3. Technical Breakdown

After analyzing the router firmware (using tools like binwalk, strings, and reverse engineering), researchers found that the web server’s handling function for /goform/DhcpListClient copies the value of the list1 parameter into a fixed-size stack buffer—without checking if the input fits!

Here’s a simplified pseudo-code version of what Tenda does in its firmware

void handle_DhcpListClient(request) {
    char buf[256];
    strcpy(buf, request->list1);
    // ... process buf
}

Notice: strcpy() just keeps copying until it sees a null byte—all without checking the buffer size! If list1 is longer than 256 characters, it will overwrite adjacent memory.


Example of a Malicious Curl Request

curl -X POST "http://192.168..1/goform/DhcpListClient"; \
     -d "list1=$(python3 -c 'print("A"*300)')"

What If You Want To See The Crash?

You can run the curl command above. If the device resets or stops functioning until rebooted, the exploit probably worked.

Is Remote Code Execution (RCE) Possible?

In theory, yes. If you carefully design the overflow (control the stack), you could overwrite function return addresses and execute your own code (like a shell command backdoor). But real-world RCE exploits against ARM routers may need further work—like bypassing stack protections.


What can Tenda users do?

- Update firmware: Check Tenda’s support site for a fix. If a new version is available, upgrade immediately.

Isolation: Don’t expose your router’s admin interface to the WAN (internet).

- Network hygiene: Only allow trusted devices on your network, as the attack likely requires LAN access.


6. References

- CVE-2024-34944 at NVD
- Original Chinese Advisory
- Tenda Official Page for FH1206
- Buffer Overflow (OWASP)

Conclusion

CVE-2024-34944 shows how even basic checks in web interfaces are critical for router security. By sending an oversized list1 to the /goform/DhcpListClient endpoint, an attacker can crash, and maybe even hijack, your Tenda FH1206 router.

*Be sure to upgrade and stay safe—network security starts at home!*


*This post is exclusive content by chat.openai.com, written for educational purposes only. Do not attempt exploits on unauthorized equipment.*

Timeline

Published on: 05/14/2024 15:39:38 UTC
Last modified on: 08/15/2024 18:35:10 UTC