How to fix API Rate Limit Exhaustion
in .NET 8 Web API
Executive Summary
Rate limit exhaustion is a classic DoS vector where an attacker floods expensive endpoints (like auth or search) to starve system resources. In .NET 8, relying on default behavior is a death sentence for availability. We mitigate this by implementing the native Microsoft.AspNetCore.RateLimiting middleware to drop malicious traffic at the door.
The Vulnerable Pattern
[ApiController]
[Route("api/v1/auth")]
public class LoginController : ControllerBase
{
[HttpPost("login")]
public async Task Login([FromBody] Credentials creds)
{
// VULNERABILITY: No throttling. An attacker can fire 10,000 requests/second,
// hammering the DB and exhausting the thread pool.
var user = await _db.Users.FirstOrDefaultAsync(u => u.Email == creds.Email);
return Ok(user);
}
} The Secure Implementation
The fix utilizes .NET 8's built-in Rate Limiting middleware. We define a 'Fixed Window' policy named 'auth_policy' that restricts users to 5 requests per 60-second window. By setting QueueLimit to 0, we immediately reject excess traffic with a 429 status code instead of buffering requests, which would consume memory. The middleware is injected into the pipeline via UseRateLimiter() and enforced at the controller level using the [EnableRateLimiting] attribute.
// 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; }); });var app = builder.Build(); app.UseRateLimiter();
// LoginController.cs [EnableRateLimiting(“auth_policy”)] [HttpPost(“login”)] public async TaskLogin([FromBody] Credentials creds) => Ok();
Your .NET 8 Web API API
might be exposed to API Rate Limit Exhaustion
74% of .NET 8 Web API apps fail this check. Hackers use automated scanners to find this specific flaw. Check your codebase before they do.
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