Fix API Rate Limit Exhaustion in ASP.NET Core

Executive Summary

API Rate Limit Exhaustion is a trivial vector for DoS and brute-force attacks. If your endpoint doesn't throttle, an attacker can saturate your thread pool or database connections with a simple loop. In ASP.NET Core, relying on 'hope' isn't a security posture. You need hard limits at the middleware level to drop malicious traffic before it hits your business logic.

The Vulnerable Pattern

VULNERABLE CODE

[ApiController]
[Route("api/v1/auth")]
public class AuthController : ControllerBase {
    [HttpPost("login")]
    public async Task Login([FromBody] LoginRequest request) {
        // VULNERABLE: No rate limiting. 
        // An attacker can send 10,000 requests/sec to brute force passwords 
        // or exhaust server resources.
        var result = await _authService.VerifyAsync(request);
        return Ok(result);
    }
}

The Secure Implementation

The secure implementation utilizes the native 'Microsoft.AspNetCore.RateLimiting' middleware introduced in .NET 7. The 'Fixed Window' policy is configured to allow only 5 requests per 60-second window. By setting 'QueueLimit' to 0, we ensure that any requests exceeding the limit are immediately rejected with a 429 (Too Many Requests) status instead of being buffered, which protects the server's memory and thread pool from exhaustion during a burst attack.

SECURE CODE

// In Program.cs
builder.Services.AddRateLimiter(options => {
    options.RejectionStatusCode = StatusCodes.Status429TooManyRequests;
    options.AddFixedWindowLimiter("auth_policy", opt => {
        opt.Window = TimeSpan.FromSeconds(60);
        opt.PermitLimit = 5;
        opt.QueueLimit = 0;
        opt.QueueProcessingOrder = QueueProcessingOrder.OldestFirst;
    });
});
// In AuthController.cs
[EnableRateLimiting(“auth_policy”)]
[HttpPost(“login”)]
public async Task Login([FromBody] LoginRequest request) {
return Ok(await _authService.VerifyAsync(request));
}

Protect your ASP.NET Core API

Don't rely on manual checks. GuardLabs detects API Rate Limit Exhaustion and logic flaws in seconds.

Run Free Audit

How to fix API Rate Limit Exhaustion
in ASP.NET Core

Executive Summary

The Vulnerable Pattern

The Secure Implementation

Protect your ASP.NET Core API

Verified by Ghost Labs Security Team