I ❤️ .NET

Table of Contents

1. What we gonna do?
2. Why we gonna do?
3. How we gonna do?
4. Summary

What we gonna do?

Ever returned a whole user object from your API just because it was easy? You might be exposing sensitive data you never intended to share. In this article, we'll break down what excessive data exposure is, why it's a silent GDPR violation, and how to fix it in your .NET applications.

Why we gonna do?

Excessive data exposure happens when APIs return more data than necessary—often out of convenience or code reuse. If your endpoint returns the entire user object when only the point balance is needed, you're leaking information. GDPR requires data minimization: only return what is strictly needed for the task at hand.

A common misconception? That hiding fields in the frontend is enough. If the API sends it, it's exposed. Another risk: failing to limit access by user role. If a customer service agent can see medical data just because it's on the customer object, that's a serious breach. And don't forget backups—if they're unencrypted or overexposed, all your careful API design is for nothing.

How we gonna do?

Here's how to prevent excessive data exposure in your .NET APIs:

Step 1: Use Endpoint-Specific DTOs

Never return full entity models from your API. Instead, define Data Transfer Objects (DTOs) that include only the fields needed for each endpoint.

// Bad: returns the entire user object
return Ok(user);

// Good: returns only the point balance
public class PointBalanceDto
{
    public int Points { get; set; }
}
return Ok(new PointBalanceDto { Points = user.Points });

Step 2: Implement Role-Based Authorization

Use ASP.NET Core Identity and the [Authorize(Roles = "...")] attribute to restrict access to sensitive data. Only allow users with the correct role to access certain endpoints or fields.

[Authorize(Roles = "MedicalStaff")]
[HttpGet("/api/patients/{id}/medical-info")]
public IActionResult GetMedicalInfo(int id)
{
    // ...return medical info only for authorized roles...
}

Step 3: Secure Your Backups

Always encrypt backups and restrict access. Never store backups unencrypted or in publicly accessible locations. Use strong access controls and audit backup access regularly.

// Example: encrypting backup data before saving
var encrypted = _aesEncryptor.Encrypt(backupBytes);
await _backupStorage.SaveAsync("backup.zip", encrypted);

Summary

Excessive data exposure is one of the easiest security flaws to fix—if you know what to look for. Use DTOs, enforce role-based access, and secure your backups. By minimizing what your APIs return and who can access it, you'll protect your users and stay on the right side of GDPR.