How to fix Lack of Resources & Rate Limiting
in ASP.NET Core
Executive Summary
Unrestricted resource consumption is a low-effort, high-impact kill chain. In ASP.NET Core, failing to implement rate limiting leaves your application vulnerable to Denial of Service (DoS), brute-force attacks, and API abuse. Without a throttle, an attacker can saturate your thread pool, exhaust DB connections, or spike CPU usage by flooding expensive endpoints. We're mitigating OWASP API4:2023 by hardening the middleware pipeline.
The Vulnerable Pattern
[ApiController] [Route("api/v1/search")] public class SearchController : ControllerBase { private readonly IDatabaseService _db; public SearchController(IDatabaseService db) => _db = db;[HttpGet] public async Task<IActionResult> Get([FromQuery] string query) { // VULNERABILITY: No rate limiting. // An attacker can spawn 10,000 concurrent requests to trigger expensive SQL JOINs, // leading to resource exhaustion and service unavailability. var results = await _db.PerformHeavySearchAsync(query); return Ok(results); }
}
The Secure Implementation
The secure implementation utilizes the native 'Microsoft.AspNetCore.RateLimiting' middleware introduced in .NET 7+. By defining a 'FixedWindowLimiter', we enforce a hard quota of 10 requests per 10-second window. Crucially, 'QueueLimit' is set to 0 to prevent the server from buffering excess requests in memory, which is a common vector for memory exhaustion. The 'UseRateLimiter' middleware is injected early in the pipeline to intercept and reject malicious traffic before it hits expensive business logic or database layers.
// Program.cs hardening using Microsoft.AspNetCore.RateLimiting; using System.Threading.RateLimiting;var builder = WebApplication.CreateBuilder(args);
builder.Services.AddRateLimiter(options => { options.RejectionStatusCode = StatusCodes.Status429TooManyRequests; options.AddFixedWindowLimiter(policyName: “StrictPolicy”, opt => { opt.PermitLimit = 10; opt.Window = TimeSpan.FromSeconds(10); opt.QueueProcessingOrder = QueueProcessingOrder.OldestFirst; opt.QueueLimit = 0; // Drop immediately to save memory }); });
var app = builder.Build(); app.UseRateLimiter();
// Controller Implementation [ApiController] [Route(“api/v1/search”)] [EnableRateLimiting(“StrictPolicy”)] public class SearchController : ControllerBase { [HttpGet] public IActionResult Get([FromQuery] string query) => Ok(“Secure results”); }
Your ASP.NET Core API
might be exposed to Lack of Resources & Rate Limiting
74% of ASP.NET Core apps fail this check. Hackers use automated scanners to find this specific flaw. Check your codebase before they do.
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