How to Secure Your .NET Applications

1. Implement Strong Authentication and Authorisation

Security begins with ensuring only the right people access your application. .NET offers robust options for managing identity and access control.

Use ASP.NET Core Identity for user and role management.
Integrate external providers like Microsoft, Google, GitHub via OAuth 2.0 or OpenID Connect.
Prefer policy-based authorisation over simple role checks for more granular control.

services.AddAuthentication("Cookies")
    .AddCookie("Cookies", options => {
        options.LoginPath = "/Account/Login";
    });

[Authorize(Policy = "AdminOnly")]
public IActionResult AdminDashboard() => View();

2. Protect Sensitive Data

Your app likely handles personal or confidential data. It’s crucial to protect it both during transmission and while stored.

Use HTTPS to encrypt data in transit (see section 4).
Store passwords using ASP.NET Identity’s built-in hashing.
Use the Data Protection API for encrypting custom data like tokens.

var protector = _dataProtectionProvider.CreateProtector("MyApp.Purpose");
var protectedData = protector.Protect("my-secret-data");
var unprotected = protector.Unprotect(protectedData);

3. Prevent Common Attacks

Many attacks can be mitigated by using .NET’s security features correctly.

SQL Injection: Use Entity Framework Core with LINQ or parameterised queries.
Cross-Site Scripting (XSS): Razor views automatically encode content. Avoid @Html.Raw() unless necessary.
Cross-Site Request Forgery (CSRF): Enabled by default with [ValidateAntiForgeryToken].
Content Security Policy (CSP): Implement CSP headers to mitigate advanced XSS attacks.

var user = await _context.Users
    .Where(u => u.Email == email)
    .FirstOrDefaultAsync();

4. Enforce HTTPS and Secure Headers

Ensuring encrypted communication and proper HTTP headers is vital for protecting user data.

app.UseHttpsRedirection();
app.UseHsts(); // Adds HTTP Strict Transport Security

Production Example (appsettings.json + Startup)

"Kestrel": {
  "Endpoints": {
    "Https": {
      "Url": "https://*:5001",
      "Certificate": {
        "Path": "certs/yourcert.pfx",
        "Password": "yourpassword"
      }
    }
  }
}

Add secure headers using middleware like NWebsec.

5. Manage Secrets Securely

Avoid hardcoding secrets like connection strings or API keys in your codebase.

Use .NET Secret Manager for local development.
Use Environment Variables in staging or production.
Use Azure Key Vault for secure, scalable secret management.

var secret = configuration["MySecret"];

Example with Azure Key Vault

builder.Configuration.AddAzureKeyVault(
    new Uri("https://<your-vault>.vault.azure.net/"),
    new DefaultAzureCredential());

6. Keep Dependencies Up to Date

Outdated packages are a common entry point for attackers. Stay current using automated tools:

dotnet list package --vulnerable
GitHub Dependabot
OWASP Dependency-Check

7. Add Logging and Monitoring

Proactive logging helps you detect and respond to suspicious activity.

Log failed logins, access denials, and other events.
Use Serilog, NLog, or built-in logging with Microsoft.Extensions.Logging.

Log.Logger = new LoggerConfiguration()
    .WriteTo.Console()
    .CreateLogger();

Cloud-based monitoring options

Azure Application Insights
Sentry, Datadog, Seq

✅ Security Checklist

Before deploying your .NET app, review the following:

HTTPS is enforced
Secrets are not in source control
Authentication & Authorisation are in place
CSRF and XSS protections are active
SQL access is parameterised or via EF Core
Secure headers (CSP, HSTS, etc.) are configured
Dependencies are up to date
Monitoring/logging is active

Tools & Resources

Final Thoughts

Security is a journey, not a destination. By following these best practices, you’ll significantly reduce risk and build trust with your users. As threats evolve, so should your defences. Keep your knowledge up to date, review your code regularly, and never stop improving.