Prevent DDos

[AbrarJahin]

https://madskristensen.net/blog/block-dos-attacks-easily-in-aspnet/

[AbrarJahin]

region Using

using System; using System.Web; using System.Collections.Generic; using System.Collections.Specialized; using System.Timers;

endregion

///

/// Block the response to attacking IP addresses. ///

public class DosAttackModule : IHttpModule {

region IHttpModule Members

void IHttpModule.Dispose() { // Nothing to dispose; }

void IHttpModule.Init(HttpApplication context) { context.BeginRequest += new EventHandler(context_BeginRequest); }

endregion

region Private fields

private static Dictionary<string, short> _IpAdresses = new Dictionary<string, short>(); private static Stack _Banned = new Stack(); private static Timer _Timer = CreateTimer(); private static Timer _BannedTimer = CreateBanningTimer();

endregion

private const int BANNED_REQUESTS = 10; private const int REDUCTION_INTERVAL = 1000; // 1 second private const int RELEASE_INTERVAL = 5 60 1000; // 5 minutes

private void context_BeginRequest(object sender, EventArgs e) { string ip = HttpContext.Current.Request.UserHostAddress; if (_Banned.Contains(ip)) { HttpContext.Current.Response.StatusCode = 403; HttpContext.Current.Response.End(); }

CheckIpAddress(ip);

}

///

/// Checks the requesting IP address in the collection /// and bannes the IP if required. ///

private static void CheckIpAddress(string ip) { if (!_IpAdresses.ContainsKey(ip)) { _IpAdresses[ip] = 1; } else if (_IpAdresses[ip] == BANNED_REQUESTS) { _Banned.Push(ip); _IpAdresses.Remove(ip); } else { _IpAdresses[ip]++; } }

region Timers

///

/// Creates the timer that substract a request /// from the _IpAddress dictionary. ///

private static Timer CreateTimer() { Timer timer = GetTimer(REDUCTION_INTERVAL); timer.Elapsed += new ElapsedEventHandler(TimerElapsed); return timer; }

///

/// Creates the timer that removes 1 banned IP address /// everytime the timer is elapsed. ///

/// private static Timer CreateBanningTimer() { Timer timer = GetTimer(RELEASE_INTERVAL); timer.Elapsed += delegate { _Banned.Pop(); }; return timer; }

///

/// Creates a simple timer instance and starts it. ///

/// The interval in milliseconds. private static Timer GetTimer(int interval) { Timer timer = new Timer(); timer.Interval = interval; timer.Start();

return timer;

}

///

/// Substracts a request from each IP address in the collection. ///

private static void TimerElapsed(object sender, ElapsedEventArgs e) { foreach (string key in _IpAdresses.Keys) { _IpAdresses[key]--; if (_IpAdresses[key] == 0) _IpAdresses.Remove(key); } }

endregion

}