Helmet for security headers in Express - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is Helmet in Express?

Helmet is a middleware for Express that helps secure your app by setting various HTTP headers to protect against common web vulnerabilities.

intermediate

Name two HTTP headers that Helmet sets to improve security.

Helmet sets headers like Content-Security-Policy (CSP) to control resources the browser can load, and X-Frame-Options to prevent clickjacking attacks.

beginner

How do you add Helmet to an Express app?

You install Helmet with npm, then require it and use it as middleware: <br><code>const helmet = require('helmet');<br>app.use(helmet());</code>

beginner

True or False: Helmet automatically fixes all security issues in your Express app.

False. Helmet helps by setting security headers but you still need to write secure code and handle other security aspects.

intermediate

What does the Content-Security-Policy header do when set by Helmet?

It tells the browser which sources of content (like scripts, images) are allowed to load, helping prevent cross-site scripting (XSS) attacks.

What is the main purpose of Helmet in an Express app?

A To serve static files

B To handle database connections

C To manage user sessions

D To add security headers to HTTP responses

Helmet's main role is to set security-related HTTP headers to protect your app.

Which of these headers is NOT set by Helmet by default?

A X-Content-Type-Options

B X-Powered-By

C Strict-Transport-Security

D Content-Security-Policy

Helmet disables the X-Powered-By header to hide Express usage, it does not set it.

How do you apply Helmet middleware in an Express app?

A app.use(helmet());

B app.helmet();

C helmet(app);

D app.set('helmet', true);

You use Helmet by calling app.use(helmet()) after requiring it.

Which security risk does Content-Security-Policy help prevent?

A Denial of Service

B SQL Injection

C Cross-Site Scripting (XSS)

D Man-in-the-Middle

CSP restricts sources of executable scripts, reducing XSS risks.

True or False: Helmet replaces the need for other security practices in your app.

A False

B Only for small apps

C True

D Only if using HTTPS

Helmet helps but does not replace secure coding and other security measures.

Explain how Helmet improves security in an Express app and name at least two headers it sets.

Think about what headers control in the browser.

Describe the steps to add Helmet to a new Express project and why it is important.

Focus on setup and purpose.

Practice

1. What is the main purpose of using helmet in an Express app?

easy

A. To add security headers that protect the app from common web attacks

B. To handle database connections securely

C. To improve the app's performance by caching

D. To manage user authentication and sessions

Solution

1. Step 1: Understand Helmet's role

   Helmet is a middleware that adds HTTP headers to improve security.

2. Step 2: Identify the main benefit

   These headers help protect against attacks like cross-site scripting and clickjacking.

3. Final Answer:

   To add security headers that protect the app from common web attacks -> Option A

4. Quick Check:

   Helmet adds security headers = D [OK]

Hint: Helmet = security headers for Express apps [OK]

Common Mistakes:

• Confusing Helmet with authentication middleware
• Thinking Helmet manages database or caching
• Assuming Helmet improves app speed

2. Which of the following is the correct way to use Helmet in an Express app?

easy

A. import helmet from 'helmet'; app.use(helmet());

B. const helmet = require('helmet'); app.use(helmet());

C. const helmet = require('helmet'); app.use(helmet);

D. import helmet from 'helmet'; app.use(helmet);

Solution

1. Step 1: Check import syntax

   In CommonJS, use const helmet = require('helmet');. In ES modules, use import helmet from 'helmet';.

2. Step 2: Use helmet as middleware function

   Helmet must be called as a function: helmet(), then passed to app.use().

3. Final Answer:

   const helmet = require('helmet'); app.use(helmet()); -> Option B

4. Quick Check:

   Require + call helmet() = A [OK]

Hint: Require helmet and call it as a function in app.use() [OK]

Common Mistakes:

• Forgetting to call helmet() as a function
• Using require with ES module import style
• Passing helmet without parentheses to app.use

3. Given this Express code snippet, what HTTP header will be set by Helmet by default?

import express from 'express';
import helmet from 'helmet';
const app = express();
app.use(helmet());
app.get('/', (req, res) => res.send('Hello'));
app.listen(3000);

medium

A. Content-Security-Policy

B. X-Powered-By

C. Access-Control-Allow-Origin

D. X-DNS-Prefetch-Control

Solution

1. Step 1: Recall Helmet default headers

   Helmet sets several headers by default, including X-DNS-Prefetch-Control to control DNS prefetching.

2. Step 2: Identify headers not set by default

   Content-Security-Policy is not set by default; X-Powered-By is removed by Helmet; Access-Control-Allow-Origin is for CORS, not Helmet.

3. Final Answer:

   X-DNS-Prefetch-Control -> Option D

4. Quick Check:

   Helmet default header = X-DNS-Prefetch-Control [OK]

Hint: Helmet sets X-DNS-Prefetch-Control by default [OK]

Common Mistakes:

• Assuming Content-Security-Policy is set by default
• Thinking Helmet adds CORS headers
• Confusing X-Powered-By removal with setting

4. What is wrong with this code snippet using Helmet?

import express from 'express';
import helmet from 'helmet';
const app = express();
app.use(helmet);
app.listen(3000);

medium

A. Helmet middleware is not called as a function

B. Helmet is not imported correctly

C. Express app is not created properly

D. app.listen is missing a callback

Solution

1. Step 1: Check Helmet usage

   The code uses app.use(helmet); but Helmet must be called as a function: helmet().

2. Step 2: Verify other parts

   Helmet import is valid; Express app creation is valid; app.listen callback is optional.

3. Final Answer:

   Helmet middleware is not called as a function -> Option A

4. Quick Check:

   Use helmet() in app.use() [OK]

Hint: Always call helmet() before app.use() [OK]

Common Mistakes:

• Passing helmet without parentheses to app.use
• Confusing import styles
• Thinking app.listen needs a callback

5. You want to disable the Content-Security-Policy header in Helmet but keep all other default headers. Which code correctly achieves this?

hard

A. app.use(helmet({ disable: ['contentSecurityPolicy'] }));

B. app.use(helmet.disable('contentSecurityPolicy'));

C. app.use(helmet({ contentSecurityPolicy: false }));

D. app.use(helmet().disable('contentSecurityPolicy'));

Solution

1. Step 1: Understand Helmet options

   Helmet allows disabling specific headers by passing options with the header name set to false.

2. Step 2: Identify correct syntax

   The correct way is helmet({ contentSecurityPolicy: false }). Other options shown are invalid methods or syntax.

3. Final Answer:

   app.use(helmet({ contentSecurityPolicy: false })); -> Option C

4. Quick Check:

   Disable header via option false = A [OK]

Hint: Disable headers by setting option to false in helmet() [OK]

Common Mistakes:

• Trying to call disable() method on helmet
• Passing disable array option (not supported)
• Calling disable on helmet() instance