Random

#include <stdio.h>

int main(){
unsigned int random;
random = rand();    // random value!

unsigned int key=0;
scanf("%d", &key);

if( (key ^ random) == 0xdeadbeef ){
printf("Good!\n");
system("/bin/cat flag");
return 0;
}

printf("Wrong, maybe you should try 2^32 cases.\n");
return 0;
}

How to Exploit

1. srand() 함수가 없으므로 사실 난수가 아니다. gdb로 bp 걸어서 난수가 0x6b8b4567이라는 것을 알았다. 0x6b8b4567 ^ 0xdeadbeef = 0xb526fb88

Exploit Code

random@prowl:~$ ./random
3039230856

Capture The Flag

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