Stop iFrame Brute Force Attacks

TL;DR

An attacker is using an iFrame to launch a brute force attack against your website. This guide shows you how to identify and block this type of attack, focusing on server-side configuration and Content Security Policy (CSP).

Understanding the Attack

Attackers embed malicious code within an iFrame hosted on their own server. Your users visit a page containing this iFrame. The iFrame then attempts to guess usernames and passwords by repeatedly submitting login forms, often at high speed. This bypasses client-side security measures like CAPTCHAs.

Step 1: Identify the Attack in Logs

1. Check your web server logs: Look for a large number of POST requests to your login endpoint originating from a single IP address or a small range of IPs.
2. Examine request patterns: Brute force attacks often have predictable patterns – many failed login attempts in quick succession.
3. Identify the referring domain: The logs should show that these requests are coming from an external domain hosting the malicious iFrame.

Example log entry (Apache):

192.168.1.10 - - [10/Oct/2023:14:55:32 +0000] "POST /login HTTP/1.1" 401 256 "http://attackerdomain.com/malicious_iframe.html" ...

Step 2: Block the Attacking IP Address(es)

1. Firewall Rules: Add rules to your firewall (e.g., iptables, ufw, AWS Security Groups, Cloudflare Firewall) to block traffic from the attacker’s IP address(es).
2. Web Server Configuration: Configure your web server (e.g., Apache .htaccess, Nginx config) to deny access based on IP address.

Example .htaccess rule:

<Limit POST /login>
  Order Deny,Allow
  Deny from 192.168.1.10
  Allow from all
</Limit>

Step 3: Implement Content Security Policy (CSP)

CSP is the most effective long-term solution. It tells the browser which sources are allowed to load resources, preventing your page from loading content from untrusted domains.

1. Define a strict CSP: Start with a restrictive policy and gradually allow trusted sources as needed.
2. Block iFrame embedding: Specifically prevent your site from being embedded in an iFrame from unknown origins.

Example CSP header:

Content-Security-Policy: default-src 'self'; frame-ancestors 'none';

This policy allows resources only from your own domain and prevents any iFrame embedding.

Step 4: Rate Limiting

1. Implement rate limiting on login endpoints: Limit the number of login attempts allowed per IP address within a specific timeframe.
2. Use web server modules or third-party tools: Apache’s mod_ratelimit, Nginx’s limit_req_zone and limit_conn_zone are useful options.

Example Nginx rate limiting configuration:

http {
  ...
  limit_req_zone $binary_remote_addr zone=mylimit:10m rate=5r/s;

  server {
    ...
    location /login {
      limit_req zone=mylimit burst=10 nodelay;
      ...
    }
  }
}

This limits login attempts to 5 per second, with a burst allowance of 10.

Step 5: CAPTCHA (as an additional layer)

1. Implement CAPTCHA on the login form: While not foolproof against sophisticated attacks, it adds another hurdle for automated bots.
2. Use a reputable CAPTCHA provider: Google reCAPTCHA is a common choice.

Step 6: Monitor and Refine

Regularly review your logs, CSP reports, and firewall rules to identify new attack patterns and adjust your security measures accordingly. cyber security is an ongoing process.