CSRF protection in Ruby on Rails - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does CSRF stand for and what problem does it solve?

CSRF stands for Cross-Site Request Forgery. It protects web applications by preventing unauthorized commands from being transmitted from a user that the web app trusts.

beginner

How does Rails protect against CSRF attacks by default?

Rails includes a CSRF token in forms and verifies this token on the server for each non-GET request. If the token is missing or invalid, Rails rejects the request.

intermediate

What is the purpose of the protect_from_forgery method in Rails?

The protect_from_forgery method enables CSRF protection in Rails controllers by checking the CSRF token on requests that change data.

intermediate

Why should CSRF tokens be unique per user session?

Unique tokens per session ensure that attackers cannot guess or reuse tokens from other users, making CSRF attacks much harder to perform.

advanced

How can you disable CSRF protection for specific actions in a Rails controller?

You can disable CSRF protection for specific actions by using skip_before_action :verify_authenticity_token, only: [:action_name] in the controller.

What does Rails check to protect against CSRF attacks?

A User's browser type

B User's IP address

C A secret token included in forms and headers

D The request URL

Rails uses a secret CSRF token included in forms and headers to verify requests.

Which HTTP methods does Rails typically protect with CSRF tokens?

A POST, PUT, PATCH, DELETE

B All HTTP methods

C OPTIONS only

D GET and HEAD

Rails protects state-changing methods like POST, PUT, PATCH, and DELETE with CSRF tokens.

What happens if a CSRF token is missing or invalid in a Rails request?

A The user is redirected to the homepage

B The request is processed normally

C Rails logs a warning but processes the request

D Rails raises an exception and rejects the request

Rails raises an exception and rejects requests with missing or invalid CSRF tokens.

How can you include a CSRF token in an HTML form in Rails views?

A Manually add a hidden input with the token

B Use Rails form helpers like <code>form_with</code> or <code>form_for</code>

C Add a meta tag in the head

D No need to include it in forms

Rails form helpers automatically include the CSRF token as a hidden field.

When might you want to disable CSRF protection in a Rails controller?

A For API endpoints that use other authentication methods

B For all user-facing forms

C For GET requests

D Never disable CSRF protection

API endpoints often disable CSRF protection because they use tokens or other methods for security.

Explain how Rails uses CSRF tokens to protect web applications from attacks.

Think about what Rails adds to forms and checks on the server.

Describe how you can manage CSRF protection in a Rails controller, including enabling and disabling it.

Consider controller methods that control CSRF checks.

Practice

1. What is the main purpose of CSRF protection in a Rails application?

easy

A. To prevent unauthorized commands from being executed by malicious websites

B. To speed up database queries

C. To improve the user interface design

D. To encrypt user passwords

Solution

1. Step 1: Understand CSRF meaning

   CSRF stands for Cross-Site Request Forgery, which is an attack where unauthorized commands are sent from a user that the web application trusts.

2. Step 2: Identify CSRF protection goal

   The goal of CSRF protection is to stop these unauthorized commands from malicious websites.

3. Final Answer:

   To prevent unauthorized commands from being executed by malicious websites -> Option A

4. Quick Check:

   CSRF protection = prevent unauthorized commands [OK]

Hint: CSRF stops bad actions from other sites [OK]

Common Mistakes:

• Confusing CSRF with password encryption
• Thinking it speeds up queries
• Assuming it improves UI design

2. Which line of code correctly enables CSRF protection in a Rails controller?

easy

A. use_csrf_token()

B. enable_csrf_protection true

C. csrf_protect = true

D. protect_from_forgery with: :exception

Solution

1. Step 1: Recall Rails CSRF syntax

   Rails uses the method protect_from_forgery with options like :exception to enable CSRF protection.

2. Step 2: Match correct syntax

   Only protect_from_forgery with: :exception is valid Rails syntax to enable CSRF protection.

3. Final Answer:

   protect_from_forgery with: :exception -> Option D

4. Quick Check:

   Enable CSRF = protect_from_forgery [OK]

Hint: Use protect_from_forgery with: :exception [OK]

Common Mistakes:

• Using non-existent methods like enable_csrf_protection
• Assigning variables instead of calling method
• Calling undefined functions like use_csrf_token()

3. Given this Rails form code snippet, what happens if the CSRF token is missing or invalid?

<%= form_with url: '/posts' do |form| %>
  <%= form.text_field :title %>
  <%= form.submit 'Create' %>
<% end %>

medium

A. The form submits successfully without any error

B. Rails raises an ActionController::InvalidAuthenticityToken error

C. The form data is saved but with a warning in logs

D. The form redirects to the home page silently

Solution

1. Step 1: Understand form_with and CSRF token

   Rails automatically includes a CSRF token in forms created with helpers like form_with.

2. Step 2: Effect of missing or invalid token

   If the token is missing or invalid, Rails raises an ActionController::InvalidAuthenticityToken error to block the request.

3. Final Answer:

   Rails raises an ActionController::InvalidAuthenticityToken error -> Option B

4. Quick Check:

   Missing CSRF token = InvalidAuthenticityToken error [OK]

Hint: Missing token causes InvalidAuthenticityToken error [OK]

Common Mistakes:

• Assuming form submits without error
• Thinking data saves with warning
• Believing it redirects silently

4. You see this error in your Rails app: ActionController::InvalidAuthenticityToken. Which fix will most likely solve the problem?

medium

A. Ensure your forms include the CSRF token by using Rails form helpers

B. Remove the CSRF token from your forms

C. Add protect_from_forgery with: :exception in ApplicationController

D. Disable CSRF protection in config

Solution

1. Step 1: Identify cause of InvalidAuthenticityToken

   This error happens when the CSRF token is missing or invalid in the form submission.

2. Step 2: Choose fix to include CSRF token

   Using Rails form helpers like form_with automatically includes the CSRF token, fixing the error.

3. Final Answer:

   Ensure your forms include the CSRF token by using Rails form helpers -> Option A

4. Quick Check:

   Fix InvalidAuthenticityToken = include CSRF token [OK]

Hint: Use Rails form helpers to add CSRF token automatically [OK]

Common Mistakes:

• Adding protect_from_forgery again when already present
• Removing CSRF token which causes error
• Disabling protection instead of fixing token

5. You want to allow JSON API requests in your Rails app without CSRF errors but keep protection for HTML forms. Which is the best way to do this?

hard

A. Manually add CSRF tokens to JSON requests

B. Disable CSRF protection globally

C. Use protect_from_forgery with: :null_session and handle API authentication separately

D. Use protect_from_forgery with: :exception and skip CSRF check for JSON requests

Solution

1. Step 1: Understand CSRF and API requests

   CSRF tokens are mainly for browser forms; API JSON requests often don't use them and need different handling.

2. Step 2: Choose best Rails approach

   Using protect_from_forgery with: :null_session disables CSRF exceptions for APIs but keeps protection for forms, requiring separate API authentication.

3. Final Answer:

   Use protect_from_forgery with: :null_session and handle API authentication separately -> Option C

4. Quick Check:

   API JSON + CSRF = null_session + separate auth [OK]

Hint: Use null_session for APIs, keep exception for forms [OK]

Common Mistakes:

• Disabling CSRF protection globally
• Trying to add CSRF tokens manually to JSON
• Skipping CSRF only without alternative auth