> For the complete documentation index, see [llms.txt](https://docs.cooku222.kr/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.cooku222.kr/security/misc/dreamhack/dreamhack-addition-quiz.md).

# \[Dreamhack] addition-quiz

{% embed url="<https://dreamhack.io/wargame/challenges/1114>" %}

```
// Name: chall.c
// Compile Option: gcc chall.c -o chall -fno-stack-protector

#include <stdio.h>
#include <signal.h>
#include <stdlib.h>
#include <fcntl.h>
#include <unistd.h>
#include <time.h>

#define FLAG_SIZE 0x45

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

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

    signal(SIGALRM, alarm_handler);
}

int main(void) {
    int fd;
    char *flag;

    initialize();
    srand(time(NULL)); 

    flag = (char *)malloc(FLAG_SIZE);
    fd = open("./flag", O_RDONLY);
    read(fd, flag, FLAG_SIZE);
    close(fd);

    int num1 = 0;
    int num2 = 0;
    int inpt = 0; 

    for (int i = 0; i < 50; i++){
        alarm(1);
        num1 = rand() % 10000;
        num2 = rand() % 10000;
        printf("%d+%d=?\n", num1, num2);
        scanf("%d", &inpt);

        if(inpt != num1 + num2){
            printf("Wrong...\n");
            return 0;
        }
    } 
    
    puts("Nice!");
    puts(flag);

    return 0;
}
```

서버가 생성한 랜덤한 4자리 숫자를 받은 다음 두 숫자를 더해서 합을 서버에게 다시 보내준다. 그 보낸 값이 scanf(%d)로 들어가서 wrong이 출력 안 되도록 익스를 짜면 된다.

&#x20;

**exploit.py**

```
from pwn import *

#원격 서버에 연결

conn = remote('host3.dreamhack.games', 15810)

for _ in range(50):
	#서버로부터 문제를 받음
    question = conn.recvline().decode().strip()
	
    #'=' 기준으로 숫자를 분리
    num_str, _ = question.split('=')

	#'+' 기호를 기준으로 숫자를 분리
    num1, num2 = map(int, num_str.split('+'))

	#덧셈을 계산하고 결과를 서버에 전송
    conn.sendline(str(num1 + num2))

#결과를 출력
print(conn.recvall().decode())
```


---

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