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Re: pen testing & obfuscated shell code
From: Marius Huse Jacobsen <mahuja () c2i net>
Date: Mon, 9 Feb 2004 22:07:14 -0800

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Hello Don,

Friday, January 30, 2004, 5:44:53 AM, you wrote:

DP> Hello group, have a question to ask which is about using obfuscated shell code during a
DP> pen test. Do any of you actually use home cooked obfuscated shell code during a pen test?
DP> By that I mean do you replace the known sled of x90 with another 1 byte instruction that
DP> won't affect the egg?

There are many instructions that would fit the bill... Incrementing
and decrementing registers, for example. To avoid further filters,
you may wish to alternate. E.g.
NOP
INC EAX
INC EDX
NOP
NOP
INC EAX
DEC EDX
INC EAX
XOR EAX,EAX

The clue is that the instruction, in machine code, should be one byte
only. Simply because if there were two, there would be a chance it
"landed" on the odd byte.

- --
Best regards,
 Marius                            mailto:mahuja () c2i net

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