Secure Your ASP.NET MVC App

TL;DR

This guide provides practical steps to improve the cyber security of your ASP.NET MVC application. It covers common vulnerabilities and how to address them, focusing on input validation, authentication, authorisation, data protection, and more.

1. Input Validation – Stop Bad Data at the Door

Input validation is crucial. Never trust user-supplied data. Validate all input on both the client-side (for usability) and, critically, on the server-side (for security).

• Client-Side Validation: Use Data Annotations in your models for basic checks.
• Server-Side Validation: Always re-validate data in your controller actions. Don’t rely solely on client-side validation as it can be bypassed.

[Required(ErrorMessage = "Please enter a value.")]
[StringLength(50, MinimumLength = 3, ErrorMessage = "Must be between 3 and 50 characters.")]
public string Name { get; set; }

2. Authentication – Verify Who They Are

Implement robust authentication to confirm user identities.

• Use ASP.NET Identity: This provides a secure framework for managing users, passwords, and roles.
• Strong Password Policies: Enforce minimum length, complexity requirements (uppercase, lowercase, numbers, symbols), and prevent common passwords.
• Two-Factor Authentication (2FA): Add an extra layer of security by requiring a second verification method (e.g., code from an authenticator app).
• Lockout Policies: Prevent brute-force attacks by locking accounts after multiple failed login attempts.

3. Authorisation – Control What They Can Do

Authorisation determines what authenticated users are allowed to access.

• Role-Based Access Control (RBAC): Assign users to roles and grant permissions based on those roles.
• Attribute-Based Access Control: Use attributes like [Authorize(Roles = "Admin"] to restrict access to controllers or actions.

[Authorize(Roles = "Admin,Editor"]

4. Data Protection – Keep Sensitive Information Safe

Protect sensitive data both in transit and at rest.

• HTTPS: Always use HTTPS to encrypt communication between the client and server.
• Encryption: Encrypt sensitive data stored in your database or files using appropriate algorithms (e.g., AES).
• Data Masking/Redaction: Protect Personally Identifiable Information (PII) by masking or redacting it when displayed to users who don’t need full access.

5. Cross-Site Scripting (XSS) – Prevent Malicious Code Injection

XSS attacks allow attackers to inject malicious scripts into your application.

• Output Encoding: Encode user input before displaying it on the page. Use HtmlEncode or similar methods.
• Content Security Policy (CSP): Define a whitelist of trusted sources for scripts, styles, and other resources to prevent loading malicious content. Add this as an HTTP header.

6. SQL Injection – Block Database Attacks

SQL injection attacks allow attackers to manipulate database queries.

• Use Parameterised Queries: Always use parameterised queries (or stored procedures) with your data access technology (e.g., Entity Framework). Never concatenate user input directly into SQL queries.

//Good - using parameters
using (var connection = new SqlConnection(connectionString))
{
  command.CommandText = "SELECT * FROM Users WHERE Username = @Username";
  command.Parameters.AddWithValue("@Username", username);
}

7. Cross-Site Request Forgery (CSRF) – Protect Against Unauthorized Actions

CSRF attacks trick users into performing unintended actions.

• Anti-Forgery Tokens: Use ASP.NET MVC’s built-in anti-forgery tokens in your forms and AJAX requests.

8. Session Management – Secure User Sessions

Manage user sessions securely.

• Session Timeout: Set appropriate session timeout values to automatically log users out after a period of inactivity.
• Secure Cookies: Use secure cookies (HttpOnly and Secure flags) to protect session IDs from being stolen by client-side scripts or transmitted over insecure connections.

9. Error Handling – Don’t Reveal Too Much

Handle errors gracefully without exposing sensitive information.

• Custom Error Pages: Display user-friendly error pages instead of detailed stack traces.
• Logging: Log errors for debugging purposes, but avoid logging sensitive data.

10. Keep Software Up to Date

Regularly update your ASP.NET MVC framework, libraries, and operating system with the latest security patches.