Server-Side Web Attack Prevention

TL;DR

Protect your website from attacks by securing input data, using strong authentication, keeping software updated, and monitoring for suspicious activity. This guide covers common threats and practical steps to defend against them.

1. Understand Common Server-Side Attacks

Server-side attacks target the code running on your web server. Here are some key types:

• SQL Injection: Attackers insert malicious SQL code into input fields to gain access to or modify your database.
• Cross-Site Scripting (XSS): Attackers inject malicious scripts into websites viewed by other users.
• Remote Code Execution (RCE): Attackers execute arbitrary code on your server.
• File Inclusion: Attackers access or execute files they shouldn’t be able to see.
• Denial of Service (DoS) / Distributed Denial of Service (DDoS): Overwhelm the server with traffic, making it unavailable.

2. Secure Your Input Data

All data coming into your server should be treated as potentially malicious.

1. Input Validation: Check that input matches expected formats (e.g., email addresses, phone numbers).
• Whitelisting is best: Only allow known good characters and patterns.
• Blacklisting is less effective: Trying to block bad characters can be easily bypassed.
2. Escaping Output: Encode data before displaying it on a webpage to prevent XSS attacks. The specific escaping method depends on the context (HTML, JavaScript, URL).
3. Parameterized Queries/Prepared Statements: Use these when interacting with databases to prevent SQL injection. This separates code from data.

   // Example in PHP using PDO
   $stmt = $pdo->prepare('SELECT * FROM users WHERE username = :username');
   $stmt->bindParam(':username', $username);
   $stmt->execute();
   

3. Implement Strong Authentication and Authorization

1. Strong Passwords: Enforce strong password policies (length, complexity).
2. Multi-Factor Authentication (MFA): Add an extra layer of security beyond passwords.
3. Session Management: Use secure session IDs and protect against session hijacking.
   • Set the HttpOnly flag on cookies to prevent JavaScript access.
   • Use a strong random number generator for session ID creation.
4. Least Privilege: Grant users only the permissions they need to perform their tasks.

4. Keep Software Updated

Regularly update your web server, operating system, programming languages, frameworks, and libraries.

• Automated Updates: Where possible, enable automatic updates.
• Vulnerability Scanning: Use tools to identify known vulnerabilities in your software.

5. Monitor Your Server

1. Log Analysis: Regularly review server logs for suspicious activity (e.g., failed login attempts, unusual requests).
2. Intrusion Detection Systems (IDS): Use an IDS to detect and alert you to potential attacks.
3. Web Application Firewalls (WAFs): A WAF can filter malicious traffic before it reaches your server.
   • Consider using a cloud-based WAF for ease of management.

6. Secure File Uploads

File uploads are a common attack vector.

• Restrict File Types: Only allow specific, safe file types.
• Validate File Content: Check the actual content of the uploaded file to ensure it matches the expected type (don’t rely solely on the filename extension).
• Store Uploads Securely: Store uploads outside your web root and serve them through a separate domain or subdomain.

7. Implement Error Handling

Avoid displaying sensitive information in error messages.

• Generic Error Messages: Show users a friendly, generic error message instead of detailed technical details.
• Log Detailed Errors: Log detailed errors internally for debugging purposes.