Securing Captive Portals

TL;DR

Captive portals are vulnerable to attacks like man-in-the-middle (MITM) and session hijacking. Securing them requires HTTPS, strong authentication, input validation, regular updates, and monitoring for suspicious activity.

Securing Your Captive Portal: A Step-by-Step Guide

1. Enable HTTPS

• Captive portals handle sensitive information (passwords, email addresses). Never use HTTP.
• Obtain a valid SSL/TLS certificate from a trusted Certificate Authority (CA) or use Let’s Encrypt for free certificates.
• Configure your web server (e.g., Apache, Nginx) to enforce HTTPS redirection. For example, in Apache:

  RewriteEngine On
  RewriteCond %{HTTPS} off
  RewriteRule ^(.*)$ https://%{HTTP_HOST}%{REQUEST_URI} [L,R=301]

Implement Strong Authentication

• Avoid simple username/password authentication where possible.
• Consider using:
  • Social login (e.g., Google, Facebook) – but be aware of privacy implications and third-party dependencies.
  • One-Time Passwords (OTP) via SMS or email.
  • MAC address authentication (less secure, easily spoofed).
• Enforce strong password policies if using username/password:
  • Minimum length
  • Complexity requirements (uppercase, lowercase, numbers, symbols)
  • Regular password changes

Validate User Input

• Crucially important! Prevent Cross-Site Scripting (XSS), SQL Injection and other injection attacks.
• Sanitize all user input before processing it.
  • Use appropriate escaping functions for your programming language/framework. For example, in PHP:

    $username = htmlspecialchars($_POST['username'], ENT_QUOTES, 'UTF-8');

  • Validate input against expected formats (e.g., email address format).

Protect Against Session Hijacking

• Use secure session cookies:
  • Set the HttpOnly flag to prevent client-side JavaScript access.
  • Set the Secure flag to only transmit cookies over HTTPS.
  • Regenerate session IDs after login and periodically during the session.

Regularly Update Software

• Keep your web server, operating system, captive portal software, and any dependencies up-to-date with the latest security patches.
• Automate updates where possible.

Monitor for Suspicious Activity

• Log all login attempts (successful and failed).
• Monitor logs for unusual patterns or brute-force attacks.
• Implement intrusion detection/prevention systems (IDS/IPS) if feasible.

Network Segmentation

• Isolate the captive portal network from your internal network to limit the impact of a potential breach.
• Use firewalls and access control lists (ACLs) to restrict traffic flow.

Consider Two-Factor Authentication (2FA)

• Adding 2FA significantly increases security, even if passwords are compromised.