[Toddler's Bottle] input writeup

문제

Mom? how can I pass my input to a computer program?

ssh input2@pwnable.kr -p2222 (pw:guest)

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분석

input.c의 내용

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <arpa/inet.h>

int main(int argc, char* argv[], char* envp[]){
    printf("Welcome to pwnable.kr\n");
    printf("Let's see if you know how to give input to program\n");
    printf("Just give me correct inputs then you will get the flag :)\n");

    // argv
    if(argc != 100) return 0;
    if(strcmp(argv['A'],"\x00")) return 0;
    if(strcmp(argv['B'],"\x20\x0a\x0d")) return 0;
    printf("Stage 1 clear!\n");   

    // stdio
    char buf[4];
    read(0, buf, 4);
    if(memcmp(buf, "\x00\x0a\x00\xff", 4)) return 0;
    read(2, buf, 4);
        if(memcmp(buf, "\x00\x0a\x02\xff", 4)) return 0;
    printf("Stage 2 clear!\n");
   
    // env
    if(strcmp("\xca\xfe\xba\xbe", getenv("\xde\xad\xbe\xef"))) return 0;
    printf("Stage 3 clear!\n");

    // file
    FILE* fp = fopen("\x0a", "r");
    if(!fp) return 0;
    if( fread(buf, 4, 1, fp)!=1 ) return 0;
    if( memcmp(buf, "\x00\x00\x00\x00", 4) ) return 0;
    fclose(fp);
    printf("Stage 4 clear!\n");   

    // network
    int sd, cd;
    struct sockaddr_in saddr, caddr;
    sd = socket(AF_INET, SOCK_STREAM, 0);
    if(sd == -1){
        printf("socket error, tell admin\n");
        return 0;
    }
    saddr.sin_family = AF_INET;
    saddr.sin_addr.s_addr = INADDR_ANY;
    saddr.sin_port = htons( atoi(argv['C']) );
    if(bind(sd, (struct sockaddr*)&saddr, sizeof(saddr)) < 0){
        printf("bind error, use another port\n");
            return 1;
    }
    listen(sd, 1);
    int c = sizeof(struct sockaddr_in);
    cd = accept(sd, (struct sockaddr *)&caddr, (socklen_t*)&c);
    if(cd < 0){
        printf("accept error, tell admin\n");
        return 0;
    }
    if( recv(cd, buf, 4, 0) != 4 ) return 0;
    if(memcmp(buf, "\xde\xad\xbe\xef", 4)) return 0;
    printf("Stage 5 clear!\n");

    // here's your flag
    system("/bin/cat flag");   
    return 0;
}

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FL4G

참조 : [네이버블로그] 보노보노의 컴퓨터 :: pwnable.kr Toddler's bottle [input] (1) pwnlib :: 작성자 Cyb3rC4t