Need

Enforce rate limiting to control the frequency of user interactions

Context

• Usage of C# for developing robust and efficient software applications
• Usage of Microsoft.AspNetCore.Mvc for building web applications with ASP.NET Core
• Usage of System.Threading.Tasks for asynchronous programming in .NET

Description

Non compliant code

        using Microsoft.AspNetCore.Mvc;
using System.Threading.Tasks;

namespace VulnerableApp.Controllers
{
    [Route("api/[controller]")]
    [ApiController]
    public class DataController : ControllerBase
    {
        // POST api/data
        [HttpPost]
        public async Task Post([FromBody] string value)
        {
            // process the data
            await ProcessData(value);

            return Ok();
        }

        private Task ProcessData(string value)
        {
            // Simulate data processing
            return Task.CompletedTask;
        }
    }
}
        
        

The above code represents an API endpoint in an ASP.NET Core application that accepts POST requests at the route api/data. The Post method takes a string value from the request body and processes it asynchronously.

The vulnerability here is that there is no control over the frequency of interaction with this endpoint. This means that a user could potentially make an unlimited number of requests to this endpoint in a short period of time. This can lead to a Denial of Service (DoS) attack where the server is overwhelmed with requests, causing it to slow down or crash.

In addition, if the ProcessData method involves resource-intensive operations such as database writes, the lack of rate limiting could lead to resource exhaustion, further degrading the performance of the server or even causing data loss or corruption.

The system is vulnerable to automated attacks as well because bots can be programmed to make rapid, repeated requests to the endpoint. This vulnerability is often exploited in brute-force attacks, where an attacker attempts to guess a value (such as a password) by trying all possible combinations. Without rate limiting, such an attack could be carried out very quickly.

Steps

• Implement rate limiting to restrict the number of requests a user can make within a certain time frame.
• Use a middleware or filter to intercept incoming requests and check if the user has exceeded the allowed limit.
• Track the number of requests made by each user and the timestamp of the last request.
• If the user has exceeded the limit, return an appropriate error response (e.g., HTTP 429 Too Many Requests).
• Consider using a sliding window algorithm or token bucket algorithm to implement the rate limiting logic.
• Configure the rate limit values (e.g., maximum number of requests and time frame) based on your application's requirements.
• Test the rate limiting implementation to ensure it effectively restricts the frequency of user interactions.

Compliant code

        using Microsoft.AspNetCore.Mvc;
using System.Threading.Tasks;
using AspNetCoreRateLimit;
using Microsoft.Extensions.Options;

namespace VulnerableApp.Controllers
{
    [Route("api/[controller]")]
    [ApiController]
    public class DataController : ControllerBase
    {
        private readonly IClientPolicyStore _clientPolicyStore;

        public DataController(IClientPolicyStore clientPolicyStore)
        {
            _clientPolicyStore = clientPolicyStore;
        }

        // POST api/data
        [HttpPost]
        [EnableRateLimiting]
        public async Task Post([FromBody] string value)
        {
            // Check if the client has exceeded their rate limit
            if (_clientPolicyStore.IsClientRateLimited("client-id"))
            {
                return StatusCode(429, "Too Many Requests");
            }

            // process the data
            await ProcessData(value);

            return Ok();
        }

        private Task ProcessData(string value)
        {
            // Simulate data processing
            return Task.CompletedTask;
        }
    }
}
        
        

The updated code now includes rate limiting to restrict the number of requests a user can make within a certain time frame. This is achieved by using the AspNetCoreRateLimit library, which provides middleware for rate limiting based on IP address or client ID.

In the DataController constructor, we inject IClientPolicyStore, which is used to check if a client has exceeded their rate limit.

In the Post method, we first check if the client has exceeded their rate limit by calling _clientPolicyStore.IsClientRateLimited("client-id"). If the client has exceeded their limit, we return an HTTP 429 (Too Many Requests) response.

The EnableRateLimiting attribute is added to the Post method to enable rate limiting for this endpoint.

The rate limit values (e.g., maximum number of requests and time frame) can be configured in the application's configuration file.

This implementation uses a sliding window algorithm to track the number of requests made by each client and the timestamp of the last request. If a client exceeds their limit, subsequent requests will be denied until enough time has passed for the request count to fall below the limit.

This rate limiting implementation should be tested to ensure it effectively restricts the frequency of user interactions.

References

• 108. Improper control of interaction frequency