pwnable.kr-bof-Writeup

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pwnable.kr-bof-Writeup

在http://pwnable.kr/bin/bof.c得到C代码如下：

 #include <stdio.h>
 #include <string.h>
 #include <stdlib.h>
 void func(int key){
     char overflowme[];
     printf("overflow me : ");
     gets(overflowme);    // smash me!
     if(key == 0xcafebabe){
         system("/bin/sh");
     }
     else{
         printf("Nah..\n");
     }
 }
 int main(int argc, char* argv[]){
     func(0xdeadbeef);
     return ;
 }

在http://pwnable.kr/bin/bof下载文件bof，die查壳如下，无壳，为elf文件

由题目中的提示Nana told me that buffer overflow is one of the most common software vulnerability. Is that true?可知此题的漏洞为缓冲区溢出，分析C代码：

• 直接把bof拖到IDA中，通过查找关键字符串跳转到关键函数func：
• 双击a1与s查看地址如下，则二者的地址相差+0x00000008 - (-0x0000002C) = 0x34 = 52

• 因为0xCAFEBABE（即IDA中的-889275714）为小端存储，则可以在get(&s)处可构造输入 '0'*52+0xBE0xBA0xFE0xCA,在Linux中检验，可以得到flag为：daddy, I just pwned a buFFer :)

构造输入时需要注意用 cat - 维持shell；

2017-2-7 19:52;05