Server action security considerations in NextJS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a server action that securely handles a form submission.

NextJS

'use [1]';

export const submitForm = async (formData) => {
  // process formData securely
}

Drag options to blanks, or click blank then click option'

Ause

Bclient

Cstrict

Dserver

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'use client' instead of 'use server' causes the function to run on the client.

Omitting the directive makes the function run on the client by default.

The 'use server' directive marks the function as a server action in Next.js, ensuring it runs only on the server.

2fill in blank

medium

Complete the code to prevent Cross-Site Request Forgery (CSRF) in a server action.

NextJS

import { verifyCsrfToken } from 'csrf-lib';

export const submitData = async (data, [1]) => {
  verifyCsrfToken(csrfToken);
  // handle data
}

Drag options to blanks, or click blank then click option'

AcsrfToken

Bsession

Crequest

Dresponse

Attempts:

3 left

💡 Hint

Common Mistakes

Not verifying CSRF tokens allows attackers to forge requests.

Using unrelated parameters like 'session' instead of the CSRF token.

CSRF tokens must be passed to the server action to verify the request's authenticity.

3fill in blank

hard

Fix the error in the server action to avoid exposing sensitive data to the client.

NextJS

export const getUserData = async () => {
  const user = await fetchUserFromDb();
  return [1];
}

Drag options to blanks, or click blank then click option'

A{ password: user.password }

Buser.password

C{ ...user, password: undefined }

D{ ...user }

Attempts:

3 left

💡 Hint

Common Mistakes

Returning the full user object exposes sensitive data.

Returning only the password leaks secrets.

Removing or masking sensitive fields like password before returning data prevents exposing secrets to the client.

4fill in blank

hard

Fill both blanks to correctly validate user input and handle errors in a server action.

NextJS

export const createUser = async (input) => {
  if (!input.email.[1](/\S+@\S+\.\S+/)) {
    throw new Error([2]);
  }
  // create user logic
}

Drag options to blanks, or click blank then click option'

Amatch

B'Invalid email'

CstartsWith

DendsWith

Attempts:

3 left

💡 Hint

Common Mistakes

Using string methods like includes instead of regex match for validation.

Throwing errors without messages confuses debugging.

Using match with a regex checks if the email format is valid. Throwing an error with a message like 'Invalid email' informs about the issue.

5fill in blank

hard

Fill all three blanks to securely fetch user data, check authentication, and return safe data in a server action.

NextJS

export const fetchProfile = async ([1]) => {
  const user = await getUserFromSession([2]);
  if (!user) throw new Error('Unauthorized');
  return { id: user.id, name: user.name, [3]: user.[3] };
}

Drag options to blanks, or click blank then click option'

AsessionToken

Cpassword

Demail

Attempts:

3 left

💡 Hint

Common Mistakes

Returning sensitive fields like password.

Not checking if the user is authenticated before returning data.

The server action accepts a sessionToken to identify the user. It fetches the user securely and returns only safe fields like id, name, and email, excluding sensitive data like password.

Practice

1. Why should server actions in Next.js always check user authentication before proceeding?

easy

A. To allow client-side code to run faster

B. To speed up the server response time

C. To ensure only authorized users can perform sensitive operations

D. To reduce the size of the JavaScript bundle sent to the client

Solution

1. Step 1: Understand server action purpose

   Server actions run on the server to handle sensitive logic securely.

2. Step 2: Importance of authentication check

   Checking user authentication ensures only authorized users can access or modify protected data.

3. Final Answer:

   To ensure only authorized users can perform sensitive operations -> Option C

4. Quick Check:

   Authentication check = To ensure only authorized users can perform sensitive operations [OK]

Hint: Server actions protect sensitive logic by verifying users [OK]

Common Mistakes:

• Thinking authentication speeds up server response
• Confusing client-side speed with server security
• Believing authentication reduces bundle size

2. Which of the following is the correct way to define a server action in Next.js 14+?

easy

A. export async function actionName() { /* server code */ }

B. function actionName() { return Client }

C. const actionName = () => { console.log('client') }

D. export default function actionName() { return 'client' }

Solution

1. Step 1: Recognize server action syntax

   Server actions are async functions exported to run on the server.

2. Step 2: Identify correct export and async usage

   export async function actionName() { /* server code */ } correctly exports an async function for server action.

3. Final Answer:

   export async function actionName() { /* server code */ } -> Option A

4. Quick Check:

   Async export function = export async function actionName() { /* server code */ } [OK]

Hint: Server actions are async exported functions [OK]

Common Mistakes:

• Using client component syntax for server actions
• Missing async keyword in server action
• Not exporting the function

3. Given this server action code snippet, what will happen if the input is not validated?

export async function updateUser(data) {
  // No input validation
  await db.user.update({ where: { id: data.id }, data });
  return { success: true };
}

medium

A. The database may receive invalid or malicious data causing errors or security issues

B. The server will automatically reject invalid data

C. The client will validate data before sending, so no issues occur

D. The function will throw a syntax error

Solution

1. Step 1: Understand missing input validation

   Without validation, any data sent by client is accepted as-is.

2. Step 2: Consequences of no validation

   Invalid or malicious data can corrupt database or cause security vulnerabilities.

3. Final Answer:

   The database may receive invalid or malicious data causing errors or security issues -> Option A

4. Quick Check:

   Missing validation = risk of bad data [OK]

Hint: No validation risks bad data in database [OK]

Common Mistakes:

• Assuming server rejects invalid data automatically
• Believing client validation is enough
• Expecting syntax errors from bad input

4. Identify the security issue in this server action code and how to fix it:

export async function deletePost(postId) {
  await db.post.delete({ where: { id: postId } });
  return { deleted: true };
}

medium

A. Missing async keyword; fix by adding async to function

B. No return statement; fix by returning a success message

C. Incorrect database method; fix by using update instead of delete

D. Missing user authentication check; fix by verifying user identity before deleting

Solution

1. Step 1: Check for authentication or permission validation

   The code deletes a post without verifying if the user is allowed to do so.

2. Step 2: Fix by adding user identity check

   Before deleting, confirm the user is authenticated and authorized to delete the post.

3. Final Answer:

   Missing user authentication check; fix by verifying user identity before deleting -> Option D

4. Quick Check:

   Authentication missing = Missing user authentication check; fix by verifying user identity before deleting [OK]

Hint: Always check user permissions before data deletion [OK]

Common Mistakes:

• Ignoring authentication importance
• Confusing async keyword necessity
• Misunderstanding database method usage

5. You want to create a server action that updates user profile data only if the user is authenticated and the input is valid. Which approach best secures this action?

export async function updateProfile(user, data) {
  // What should you do here?
}

hard

A. Update database directly without checks for speed

B. Check if user is authenticated, validate data fields, then update database

C. Validate data on client only, then update database

D. Return success immediately and update database later asynchronously

Solution

1. Step 1: Verify user authentication inside server action

   Ensure the user object is valid and authenticated before proceeding.

2. Step 2: Validate all input data carefully

   Check each data field to prevent invalid or malicious input before updating the database.

3. Step 3: Update database only after passing checks

   Perform the update securely after authentication and validation.

4. Final Answer:

   Check if user is authenticated, validate data fields, then update database -> Option B

5. Quick Check:

   Authentication + validation = secure update [OK]

Hint: Authenticate user and validate input before DB update [OK]

Common Mistakes:

• Skipping server-side validation
• Relying only on client validation
• Updating DB without authentication