459 lines
16 KiB
C#
459 lines
16 KiB
C#
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/*
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* Secucore
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*
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* Copyright (C) 2023 Trevor Hall
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* All rights reserved.
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*
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* This software may be modified and distributed under the terms
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* of the MIT license.
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*
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*/
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using Microsoft.VisualStudio.Threading;
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using SecuCore.Shared;
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using System;
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using System.Collections.Generic;
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using System.IO;
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using System.Linq;
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using System.Net;
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using System.Net.Sockets;
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using System.Text;
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using System.Threading;
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using System.Threading.Tasks;
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namespace SecuCore.DNS
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{
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public static class Extensions
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{
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public static void WriteBigEndian16(this BinaryWriter bw, ushort littleEndian)
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{
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ushort swapped = (ushort)((littleEndian >> 8) | ((littleEndian & 255) << 8));
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bw.Write(swapped);
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}
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}
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public static class AsyncDNSResolver
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{
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//Uses Google Public DNS by Default
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private static readonly IPAddress[] DNSServers = new IPAddress[]
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{
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IPAddress.Parse("8.8.8.8"), IPAddress.Parse("8.8.4.4")
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};
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public static int Timeout { get; set; } = 120000;
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private const int minPayloadSize = 17;
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private const int maxPayloadSize = 2048;
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//Connects utilizing DNS through TCP, Port 53
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private async static Task<bool> ConnectDNS(this Socket socket, IPAddress ip)
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{
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try
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{
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await socket.ConnectAsync(ip, 53).ConfigureAwait(false);
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}
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catch (Exception ex)
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{ }
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return socket.Connected;
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}
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//The Primary Sending/Recieving Functions for this class
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private async static Task<int> Send(Socket socket, byte[] buf)
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{
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return await Task<int>.Factory.FromAsync(socket.BeginSend(buf, 0, buf.Length, SocketFlags.None, null, null), socket.EndSend).ConfigureAwait(false);
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}
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private async static Task<int> Recieve(Socket socket, byte[] buf)
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{
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int result = 0;
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try
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{
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result = await socket.ReceiveAsync(buf, SocketFlags.None).WithTimeout(TimeSpan.FromMilliseconds(Timeout)).ConfigureAwait(false);
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}
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catch (Exception ex)
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{ }
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return result;
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}
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public async static Task<string> GetFirstMXrecord(string domain)
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{
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string[] mxr = await GetMXrecords(domain).ConfigureAwait(false);
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if (mxr.Length > 0)
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return mxr[0];
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return "";
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}
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public async static Task<string> GetFirstArecord(string domain)
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{
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string[] mxr = await GetArecords(domain).ConfigureAwait(false);
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if (mxr.Length > 0)
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return mxr[0];
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return "";
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}
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public static Task<string[]> GetMXrecords(string domain)
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{
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return GetByHost(domain, QueryType.MX);
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}
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public static Task<string[]> GetArecords(string domain)
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{
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return GetByHost(domain, QueryType.A);
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}
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public static Task<string[]> GetAAAArecords(string domain)
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{
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return GetByHost(domain, QueryType.AAAA);
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}
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public static Task<string[]> GetTXTrecords(string domain)
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{
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return GetByHost(domain, QueryType.TXT);
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}
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private static readonly List<ushort> transactionids = new();
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private static SemaphoreSlim tsem = new SemaphoreSlim(1);
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private static async Task<ushort> GetTransactionID()
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{
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await tsem.WaitAsync().ConfigureAwait(false);
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try
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{
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ushort result = 0;
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while (true)
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{
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ushort tID = RandomNumbers.GetNext16();
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if (!transactionids.Contains(tID))
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{
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transactionids.Add(tID);
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if (transactionids.Count > 10000) transactionids.RemoveAt(0);
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result = tID;
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break;
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}
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}
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return result;
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}
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catch (Exception)
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{
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return RandomNumbers.GetNext16();
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}
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finally
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{
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tsem.Release();
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}
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}
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private async static Task ReturnTransactionID(ushort utid)
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{
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await tsem.WaitAsync().ConfigureAwait(false);
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try
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{
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if (transactionids.Contains(utid))
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{
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transactionids.Remove(utid);
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}
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}
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catch (Exception e)
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{ }
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tsem.Release();
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}
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public static bool ResultWasWithin(int value, ref int destination, int min, int max)
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{
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if (value >= min & value <= max)
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{
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destination = value;
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return true;
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}
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return false;
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}
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private async static Task<string[]> GetByHost(string domain, QueryType qt)
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{
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using Socket dnsSock = new(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
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if (!await dnsSock.ConnectDNS(DNSServers[RandomNumbers.GetNext(0, DNSServers.Length - 1)]).ConfigureAwait(false)) return null; // could not establish connection
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ushort transactionID = await GetTransactionID().ConfigureAwait(false);
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byte[] payload = null;
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if (!DNSPacket.CreateRecursiveQuestionPayload(transactionID, domain, qt, ref payload))
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{
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await ReturnTransactionID(transactionID).ConfigureAwait(false);
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return null; // internal error attempting to create query
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}
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if (await Send(dnsSock, payload).ConfigureAwait(false) == 0)
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{
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await ReturnTransactionID(transactionID).ConfigureAwait(false);
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return null; // error sending query
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}
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byte[] rBuf = new byte[maxPayloadSize];
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int len = 0;
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if (!ResultWasWithin(await Recieve(dnsSock, rBuf).ConfigureAwait(false), ref len, minPayloadSize, maxPayloadSize))
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{
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await ReturnTransactionID(transactionID).ConfigureAwait(false);
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return null; // result was malformed
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}
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Array.Resize<byte>(ref rBuf, len); // prune the buffer
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await ReturnTransactionID(transactionID).ConfigureAwait(false);
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DNSPacket dnsResponse = null;
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if (!DNSPacket.ParseResponse(rBuf, ref dnsResponse)) return null; // failed to parse response, or no answers were contained
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return dnsResponse.GetAnswers(qt);
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}
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}
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public enum QueryType
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{
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A = 1,
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AAAA = 28,
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CNAME = 5,
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MX = 15,
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NS = 2,
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PTR = 12,
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TXT = 16
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}
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public class DNSPacket
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{
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public ushort transactionID;
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public ushort flags;
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public ushort questions;
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public ushort answerRRs;
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public ushort authorityRRs;
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public ushort additionalRRs;
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public List<DNSQuestion> queries = new();
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public List<DNSAnswer> answers = new();
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public DNSPacket(byte[] buf)
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{
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this.ParseBuffer(buf);
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}
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public DNSPacket(ushort transactionID)
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{
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this.transactionID = transactionID;
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}
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private DNSPacket()
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{ }
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public static bool ParseResponse(byte[] buf, ref DNSPacket rPack)
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{
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try
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{
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rPack = new DNSPacket(buf);
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if (rPack.answers.Count > 0) return true;
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}
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catch (Exception e)
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{ }
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return false;
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}
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public static bool CreateRecursiveQuestionPayload(ushort transactionID, string question, QueryType qt, ref byte[] buf)
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{
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try
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{
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DNSPacket dnsQ = new(transactionID);
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dnsQ.SetRecursive();
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dnsQ.AddQuestion(question, qt);
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buf = dnsQ.GetBytes();
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return true;
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}
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catch (Exception)
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{ }
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return false;
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}
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public void SetRecursive()
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{
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flags = (ushort)(flags | System.Convert.ToUInt16(Math.Pow(2, 8)));
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}
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public void AddQuestion(string name, QueryType type)
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{
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queries.Add(new DNSQuestion(name, (ushort)type));
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questions = (ushort)queries.Count;
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}
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public byte[] GetBytes()
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{
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using System.IO.MemoryStream packetms = new();
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using BinaryWriter bw = new(packetms);
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additionalRRs = 1;
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bw.WriteBigEndian16(transactionID);
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bw.WriteBigEndian16(flags);
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bw.WriteBigEndian16(questions);
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bw.WriteBigEndian16(answerRRs);
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bw.WriteBigEndian16(authorityRRs);
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bw.WriteBigEndian16(additionalRRs);
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foreach (DNSQuestion q in queries)
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q.WriteTo(bw);
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byte[] optpacket = new byte[11];
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optpacket[2] = (byte)41;
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optpacket[3] = (byte)5;
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bw.Write(optpacket, 0, optpacket.Length);
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return packetms.ToArray();
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}
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private static uint ReadInt(ref uint index, byte[] buffer)
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{
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uint value = (uint)((buffer[index] << 24) | ((int)(buffer[index + 1]) << 16) | ((int)(buffer[index + 2]) << 8) | (int)(buffer[index + 3]));
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index += 4;
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return value;
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}
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private static ushort ReadShort(ref uint index, byte[] buffer)
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{
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ushort value = (ushort)(((int)(buffer[index]) << 8) | ((int)(buffer[(index + 1)])));
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index += 2;
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return value;
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}
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private string ReadName(ref uint idx, byte[] buf)
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{
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string @out = "";
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while (idx < buf.Length)
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{
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int lbl = buf[idx];
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idx += 1;
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if (lbl == 0) return @out;
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else if (lbl > 63)
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{
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uint namePosition = (ushort)(((lbl << 8) | buf[idx]) & 0x3FFF);
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idx += 1;
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return (@out != "" ? @out + "." : "") + ReadName(ref namePosition, buf);
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}
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else
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{
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@out += (@out != "" ? "." : "") + Encoding.ASCII.GetString(buf, (int)idx, lbl);
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idx += (uint)lbl;
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}
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}
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return @out;
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}
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public static int ByteAt(int input, int position)
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{
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if (position > 3) throw new Exception("You can only use positions 0 through 3");
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return (input >> ((3 - position) * 8)) & 255;
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}
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public void ParseBuffer(byte[] buf)
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{
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uint idx = 0;
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transactionID = ReadShort(ref idx, buf);
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flags = ReadShort(ref idx, buf);
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questions = ReadShort(ref idx, buf);
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answerRRs = ReadShort(ref idx, buf);
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authorityRRs = ReadShort(ref idx, buf);
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additionalRRs = ReadShort(ref idx, buf);
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Int16 rescode = ((short)(flags & 63));
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if (rescode > 0)
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{
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switch (rescode)
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{
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case 1:
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throw new Exception("Format Error");
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case 2:
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throw new Exception("Server Failure");
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case 3:
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throw new Exception("Name Error");
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case 4:
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throw new Exception("Not Implemented");
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case 5:
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throw new Exception("Refused");
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}
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throw new Exception("Unknown Error");
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}
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for (int i = 0; i <= questions - 1; i++)
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{
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string nm = ReadName(ref idx, buf);
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ushort qtype = ReadShort(ref idx, buf);
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ushort qclass = ReadShort(ref idx, buf);
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DNSQuestion q = new(nm, qtype);
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queries.Add(q);
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}
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for (int i = 0; i <= answerRRs - 1; i++)
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{
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DNSAnswer ans = new()
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{
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name = ReadName(ref idx, buf),
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type = ReadShort(ref idx, buf),
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@class = ReadShort(ref idx, buf),
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TTL = ReadInt(ref idx, buf),
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dataLength = ReadShort(ref idx, buf)
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};
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QueryType anstype = (QueryType)ans.type;
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if (anstype == QueryType.MX)
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{
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ans.preference = ReadShort(ref idx, buf);
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ans.rdata = ReadName(ref idx, buf);
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}
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else if (anstype == QueryType.CNAME)
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{
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ans.rdata = ReadName(ref idx, buf);
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}
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else if (anstype == QueryType.TXT)
|
|||
|
|
{
|
|||
|
|
string txtDat = "";
|
|||
|
|
int bytesRead = 0;
|
|||
|
|
while (ans.dataLength > bytesRead)
|
|||
|
|
{
|
|||
|
|
byte nLen = buf[idx];
|
|||
|
|
idx++;
|
|||
|
|
bytesRead++;
|
|||
|
|
string txtStr = System.Text.Encoding.ASCII.GetString(buf, (int)idx, nLen);
|
|||
|
|
txtDat += txtStr;
|
|||
|
|
idx += nLen;
|
|||
|
|
bytesRead += nLen;
|
|||
|
|
}
|
|||
|
|
ans.rdata = txtDat;
|
|||
|
|
}
|
|||
|
|
else if (anstype == QueryType.A && ans.dataLength == 4)
|
|||
|
|
{
|
|||
|
|
int ip32 = (int)ReadInt(ref idx, buf);
|
|||
|
|
ans.rdata = ByteAt(ip32, 0) + "." + ByteAt(ip32, 1) + "." + ByteAt(ip32, 2) + "." + ByteAt(ip32, 3);
|
|||
|
|
}
|
|||
|
|
else if (anstype == QueryType.AAAA)
|
|||
|
|
{
|
|||
|
|
byte[] ipv6 = new byte[16];
|
|||
|
|
Array.Copy(buf, idx, ipv6, 0, 16);
|
|||
|
|
IPAddress ipv6Addr = new(ipv6);
|
|||
|
|
ans.rdata = ipv6Addr.ToString();
|
|||
|
|
}
|
|||
|
|
if (ans.rdata != "") answers.Add(ans);
|
|||
|
|
}
|
|||
|
|
}
|
|||
|
|
public string[] GetAnswers(QueryType qt)
|
|||
|
|
{
|
|||
|
|
List<DNSAnswer> qualified = new List<DNSAnswer>();
|
|||
|
|
foreach(DNSAnswer answer in answers)
|
|||
|
|
{
|
|||
|
|
if (answer.type == (ushort)qt) qualified.Add(answer);
|
|||
|
|
}
|
|||
|
|
if(qt == QueryType.MX)
|
|||
|
|
{
|
|||
|
|
qualified = qualified.OrderBy(x =>
|
|||
|
|
{
|
|||
|
|
return x.preference;
|
|||
|
|
}).ToList();
|
|||
|
|
}
|
|||
|
|
return Array.ConvertAll<DNSAnswer, string>(qualified.ToArray(), new Converter<DNSAnswer, string>(d =>
|
|||
|
|
{
|
|||
|
|
return d.rdata;
|
|||
|
|
}));
|
|||
|
|
}
|
|||
|
|
}
|
|||
|
|
public class DNSQuestion
|
|||
|
|
{
|
|||
|
|
public string name;
|
|||
|
|
public ushort type;
|
|||
|
|
private readonly ushort @class = 1;
|
|||
|
|
public DNSQuestion(string name, ushort type)
|
|||
|
|
{
|
|||
|
|
this.name = name;
|
|||
|
|
this.type = type;
|
|||
|
|
}
|
|||
|
|
public void WriteTo(BinaryWriter bw)
|
|||
|
|
{
|
|||
|
|
string[] labels = name.Split('.');
|
|||
|
|
foreach (string lbl in labels)
|
|||
|
|
{
|
|||
|
|
bw.Write(System.Convert.ToByte(lbl.Length));
|
|||
|
|
bw.Write(Encoding.ASCII.GetBytes(lbl));
|
|||
|
|
}
|
|||
|
|
bw.Write(System.Convert.ToByte(0));
|
|||
|
|
bw.WriteBigEndian16(type);
|
|||
|
|
bw.WriteBigEndian16(@class);
|
|||
|
|
}
|
|||
|
|
public byte[] GetBytes()
|
|||
|
|
{
|
|||
|
|
using MemoryStream ms = new();
|
|||
|
|
using BinaryWriter bw = new(ms);
|
|||
|
|
WriteTo(bw);
|
|||
|
|
return ms.ToArray();
|
|||
|
|
}
|
|||
|
|
}
|
|||
|
|
public class DNSAnswer
|
|||
|
|
{
|
|||
|
|
public string name;
|
|||
|
|
public ushort type;
|
|||
|
|
public ushort @class;
|
|||
|
|
public UInt32 TTL;
|
|||
|
|
public ushort dataLength;
|
|||
|
|
public ushort preference;
|
|||
|
|
public string rdata;
|
|||
|
|
}
|
|||
|
|
}
|