理解并模仿 Express.js 中的 csurf 中间件

1. CSRF 和 csurf 简介

跨站请求伪造（CSRF）是一种网络安全漏洞，它允许攻击者诱导用户执行非预期的操作。csurf 是 Express.js 框架中一个流行的中间件，提供 CSRF 保护。 什么是 CSRF？

• CSRF（跨站请求伪造）是网络应用中的一种安全威胁。它诱使用户在他们认证的网站上执行不想要的操作。例如，如果登录到一个社交媒体网站，CSRF 攻击可能会诱使你不知不觉中分享帖子。

csurf 中间件是如何帮助的？

• csurf 是 Express.js 的一个中间件，有助于防止 CSRF 攻击。
• 它通过为每个用户会话添加一个独特的秘密令牌，并要求这个令牌被包含在发送到服务器的请求（如表单提交）中。
• 如果一个请求没有这个令牌，或者令牌与预期不匹配，csurf 将阻止该请求，认为它可能是 CSRF 攻击。

2. csurf 的基本原理

1. 生成令牌 : 当用户访问站点上的表单时，csurf 生成一个独特的令牌并发送给客户端（通常作为表单的一部分）。

   1. 表单的令牌生成 : 当用户访问网络应用中的表单时，csurf 生成一个独特的 CSRF 令牌。这个令牌通常包含在表单的隐藏字段中。

   2. 表单提交时的令牌提交: 用户提交表单时，CSRF 令牌与其他表单数据一起发送到服务器。

   3. 服务器上的令牌验证 : 接收到表单数据后，csurf 中间件会检查提交的 CSRF 令牌是否与它为用户会话生成和关联的令牌匹配。

   4. 安全检查 : 如果令牌匹配，意味着表单提交是合法的，来自于应用程序的实际用户界面，因此服务器处理请求。如果令牌不匹配或令牌缺失，csurf 将拒绝请求，认为它可能是 CSRF 攻击。

2. 令牌验证 : 用户提交表单时，这个令牌被发送回服务器。csurf 检查客户端的令牌是否与服务器上生成并存储的令牌匹配。如果匹配，请求被视为合法；如果不匹配，请求被阻止。

这个过程确保表单提交是安全的，并且来自你自己的应用程序，而不是外部源试图利用用户的认证会话。虽然 csurf 主要针对表单提交，但它是保护网络应用程序免受各种跨站攻击的更广泛策略的一部分。

3. 使用 csurf

要使用 csurf，首先需要安装它：

npm install csurf

然后，可以将其集成到 Express.js 应用程序中：

const express = require('express');
const csrf = require('csurf');
const app = express();

// 设置路由中间件
const csrfProtection = csrf({ cookie: true });
const parseForm = express.urlencoded({ extended: false });

// 创建路由
app.get('/form', csrfProtection, (req, res) => {
  // 将 csrfToken 传递给视图
  res.render('send', { csrfToken: req.csrfToken() });
});



app.post('/process', parseForm, csrfProtection, (req, res) => {
  res.send('数据正在处理中');
});

app.listen(3000);

4. 模仿 csurf

创建一个类似于 csurf 的简化版 CSRF 保护中间件：

1. 设置您的 Express 应用程序 首先，设置一个基本的 Express 应用程序。

const express = require('express');
const app = express();
app.use(express.json());

2. 创建一个简单的 CSRF 令牌生成器 实现一个生成独特令牌的函数。在实际场景中，出于安全考虑，这应该更复杂。

const crypto = require('crypto');

function generateCsrfToken() {
  return crypto.randomBytes(16).toString('hex');
}

3. 实现 CSRF 保护的中间件 创建生成和验证 CSRF 令牌的中间件。

const tokens = {};

function csrfMiddleware(req, res, next) {
  if (req.method === 'GET') {
    const token = generateCsrfToken();
    tokens[token] = true;
    res.locals.csrfToken = token;
    next();
  } else if (req.method === 'POST') {
    const token = req.body.csrfToken;
    if (tokens[token]) {
      delete tokens[token];
      next();
    } else {
      res.status(403).send('CSRF 令牌验证失败');
    }
  }
}

4. 应用中间件 在路由中使用中间件。

app.get('/form', csrfMiddleware, (req, res) => {
  res.send(`<form method="POST" action="/process"><input type="hidden" name="csrfToken" value="${res.locals.csrfToken}" /><input type="submit" value="提交"/></form>`);
});

app.post('/process', csrfMiddleware, (req, res) => {
  res.send('数据已成功处理');
});

5. 测试应用程序 运行应用程序并导航到 /form。提交表单应该有效，而任何没有有效 CSRF 令牌的请求都应该被拒绝。

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5. 结论

虽然这个demo提供了 CSRF 保护的基本理解并模仿了 csurf，但在生产中使用像 csurf 这样经过充分测试的库对于健壮的安全性非常重要。这个demo主要是为了理解 CSRF 保护的底层概念。

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English version: Understanding and Mimicking the csurf Middleware in Express.js

1. Introduction to CSRF and csurf

Cross-Site Request Forgery (CSRF) is a web security vulnerability that allows an attacker to induce users to perform actions that they do not intend to. csurf is a popular middleware in the Express.js framework that provides CSRF protection. What is CSRF?

• CSRF (Cross-Site Request Forgery) is a type of security threat in web applications. It tricks a user into executing unwanted actions on a web application where they are authenticated. For example, if you're logged into a social media site, a CSRF attack could trick you into unknowingly sharing a post.

How Does csurf Middleware Help?

• csurf is a middleware for Express.js that helps prevent CSRF attacks.
• It works by adding a unique, secret token to each user session and requiring that this token be included in requests (like form submissions) sent to the server.
• If a request does not have this token, or if the token doesn't match what's expected, csurf will block the request, assuming it might be a CSRF attack.

2. Basic Principle of csurf:

1. Token Generation : When a user visits a form on your site, csurf generates a unique token and sends it to the client (usually as part of the form).

   1. Token Generation for Forms : When a user accesses a form on your web application, csurf generates a unique CSRF token. This token is usually included as a hidden field in the form.

   2. Token Submission with Form: When the user submits the form, the CSRF token is sent along with the other form data to the server.

   3. Token Validation on Server : Upon receiving the form data, csurf middleware checks the submitted CSRF token against the token it had generated and associated with the user's session.

   4. Security Check : If the tokens match, it means the form submission is legitimate and came from the actual user interface of your application, so the server processes the request. If the tokens do not match or if the token is missing, csurf will reject the request, considering it a potential CSRF attack.

2. Token Validation : When the user submits the form, this token is sent back to the server. csurf checks if the token from the client matches the one it generated and stored on the server. If they match, the request is considered legitimate; if not, it's blocked.

This process ensures that the form submissions are secure and come from your own application, not an external source trying to exploit the user's authenticated session. While csurf primarily targets form submissions, it's part of a broader strategy to secure web applications against various types of cross-site attacks.

Certainly! I'll provide an article-style explanation, including the principle, usage, and a step-by-step demonstration to mimic the functionality of csurf, a middleware used in Express.js for CSRF (Cross-Site Request Forgery) protection.

3. Usage of csurf

To use csurf, you first need to install it:

npm install csurf

Then, you can integrate it into your Express.js application:

const express = require('express');
const csrf = require('csurf');
const app = express();

// Setup route middlewares
const csrfProtection = csrf({ cookie: true });
const parseForm = express.urlencoded({ extended: false });

// Create a route
app.get('/form', csrfProtection, (req, res) => {
  // Pass the csrfToken to the view
  res.render('send', { csrfToken: req.csrfToken() });
});

app.post('/process', parseForm, csrfProtection, (req, res) => {
  res.send('Data is being processed');
});

app.listen(3000);

4. Step-by-Step Demonstration: Mimicking csurf

Now, let's create a simplified version of CSRF protection middleware, similar to csurf:

1. Setup Your Express App First, set up a basic Express application.

const express = require('express');
const app = express();
app.use(express.json());

2. Creating a Simple CSRF Token Generator Implement a function to generate a unique token. In real scenarios, this should be more complex for security.

const crypto = require('crypto');

function generateCsrfToken() {
  return crypto.randomBytes(16).toString('hex');
}

3. Implementing Middleware for CSRF Protection Create middleware that generates and validates CSRF tokens.

const tokens = {};

function csrfMiddleware(req, res, next) {
  if (req.method === 'GET') {
    const token = generateCsrfToken();
    tokens[token] = true;
    res.locals.csrfToken = token;
    next();
  } else if (req.method === 'POST') {
    const token = req.body.csrfToken;
    if (tokens[token]) {
      delete tokens[token];
      next();
    } else {
      res.status(403).send('CSRF token validation failed');
    }
  }
}

4. Applying the Middleware Use the middleware in your routes.

app.get('/form', csrfMiddleware, (req, res) => {
  res.send(`<form method="POST" action="/process"><input type="hidden" name="csrfToken" value="${res.locals.csrfToken}" /><input type="submit" value="Submit"/></form>`);
});

app.post('/process', csrfMiddleware, (req, res) => {
  res.send('Data processed successfully');
});

5. Testing the Application Run the application and navigate to /form. Submitting the form should work, while any requests without the valid CSRF token should be rejected.

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5. Conclusion

While this demonstration provides a basic understanding of CSRF protection and mimics csurf, it's important to use well-tested libraries like csurf in production for robust security. This exercise is primarily for educational purposes to understand the underlying concept of CSRF protection.