Common Node.js security vulnerabilities in Node.js - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the Express framework safely.

Node.js

const express = require([1]);

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

A"express"

Bexpress

C'http'

D"fs"

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting quotes around the module name

Using wrong module names

To import Express, you must use the module name as a string: "express".

2fill in blank

medium

Complete the code to parse JSON request bodies securely using Express.

Node.js

app.use(express.[1]());

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

Atext

Bjson

Cstatic

Durlencoded

Attempts:

3 left

💡 Hint

Common Mistakes

Using urlencoded instead of json

Not using any body parser

Use express.json() middleware to safely parse JSON bodies.

3fill in blank

hard

Fix the error in this code to prevent prototype pollution in user input handling.

Node.js

const safeUser = Object.assign({}, req.body, [1]);

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

Areq.params

BObject.prototype

Cnull

Dreq.query

Attempts:

3 left

💡 Hint

Common Mistakes

Using Object.prototype causes pollution

Using req.params or req.query instead of null

Using null as the second argument prevents prototype pollution by not copying prototype properties.

4fill in blank

hard

Fill both blanks to safely set HTTP headers to prevent clickjacking and XSS attacks.

Node.js

app.use(helmet.[1]());
app.use(helmet.[2]());

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

Aframeguard

Bcors

CxssFilter

DcontentSecurityPolicy

Attempts:

3 left

💡 Hint

Common Mistakes

Using cors instead of frameguard

Confusing contentSecurityPolicy with xssFilter

helmet.frameguard() helps prevent clickjacking by setting frame options.
helmet.xssFilter() adds protections against cross-site scripting (XSS).

5fill in blank

hard

Fill all three blanks to create a secure password hash using bcrypt.

Node.js

const bcrypt = require('bcrypt');
const saltRounds = [1];
const password = req.body.password;
const hash = await bcrypt.[2](password, [3]);

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

A10

BhashSync

CsaltRounds

Dcompare

Attempts:

3 left

💡 Hint

Common Mistakes

Using compare instead of hashSync

Passing wrong salt parameter

Use 10 as salt rounds for good security.
hashSync hashes the password synchronously.
Pass saltRounds as the salt parameter.

Practice

1. Which of the following is a common security vulnerability in Node.js applications?

easy

A. Memory Leak

B. SQL Injection

C. Slow Network

D. Syntax Error

Solution

1. Step 1: Understand common vulnerabilities

   SQL Injection is a well-known security risk where attackers inject malicious SQL code.

2. Step 2: Identify relevant options

   Memory leaks and slow networks are performance issues, syntax errors are coding mistakes, not security vulnerabilities.

3. Final Answer:

   SQL Injection -> Option B

4. Quick Check:

   Common Node.js security risk = SQL Injection [OK]

Hint: Security risks often involve data injection or unauthorized access [OK]

Common Mistakes:

• Confusing performance issues with security vulnerabilities
• Thinking syntax errors are security problems
• Ignoring injection attacks

2. Which syntax correctly prevents Cross-Site Scripting (XSS) in a Node.js Express app when rendering user input in a template?

easy

A. res.send(`${escape(userInput)}`);

B. res.render('page', { data: userInput });

C. res.send(`${userInput}`);

D. res.send(userInput);

Solution

1. Step 1: Identify safe rendering method

   Escaping user input before inserting into HTML prevents XSS attacks.

2. Step 2: Compare options

   Only res.send(`
   ${escape(userInput)}`); uses an escape function to sanitize input before sending.

3. Final Answer:

   res.send(`
   ${escape(userInput)}
   `); -> Option A

4. Quick Check:

   Escape user input to prevent XSS = res.send(`
   ${escape(userInput)}
   `); [OK]

Hint: Always escape user input before rendering in HTML [OK]

Common Mistakes:

• Sending raw user input directly in HTML
• Assuming template rendering auto-escapes input
• Not using escape functions

3. What will be the output of this Node.js code snippet vulnerable to prototype pollution?

const obj = {};
const payload = JSON.parse('{"__proto__": {"polluted": "yes"}}');
Object.assign(obj, payload);
console.log({}.polluted);

medium

A. Throws an error

B. undefined

C. null

D. "yes"

Solution

1. Step 1: Understand prototype pollution

   Assigning __proto__ property modifies the prototype of all objects.

2. Step 2: Analyze code behavior

   Object.assign merges payload into obj, changing Object prototype to include polluted property.

3. Step 3: Check console.log output

   Accessing {}.polluted reads from prototype, outputs "yes".

4. Final Answer:

   "yes" -> Option D

5. Quick Check:

   Prototype pollution sets property globally = "yes" [OK]

Hint: Prototype pollution changes all objects' properties unexpectedly [OK]

Common Mistakes:

• Expecting undefined instead of polluted value
• Not recognizing __proto__ effect
• Assuming error thrown on prototype pollution

4. Identify the security flaw in this Express middleware code:

app.use((req, res, next) => {
  const token = req.headers['authorization'];
  if (token) {
    req.user = jwt.verify(token, 'secret');
  }
  next();
});

medium

A. Not checking token expiration

B. Using synchronous jwt.verify instead of async

C. Missing error handling for invalid token

D. Not sanitizing user input

Solution

1. Step 1: Review token verification

   jwt.verify can throw if token is invalid, but no try-catch is used.

2. Step 2: Identify missing error handling

   Without try-catch, invalid tokens cause app crash or unhandled exceptions.

3. Final Answer:

   Missing error handling for invalid token -> Option C

4. Quick Check:

   Always catch errors from jwt.verify [OK]

Hint: Wrap jwt.verify in try-catch to handle invalid tokens [OK]

Common Mistakes:

• Ignoring exceptions from jwt.verify
• Assuming synchronous call is insecure
• Confusing input sanitization with token validation

5. You want to secure a Node.js app against outdated package vulnerabilities. Which approach is best to keep dependencies safe?

hard

A. Run 'npm audit' regularly and update vulnerable packages

B. Ignore warnings and only update major versions yearly

C. Manually edit package-lock.json to remove vulnerabilities

D. Use only packages without any dependencies

Solution

1. Step 1: Understand package vulnerability management

   npm audit scans for known vulnerabilities in dependencies.

2. Step 2: Choose best practice

   Regularly running npm audit and updating packages fixes security issues promptly.

3. Step 3: Evaluate other options

   Ignoring warnings risks attacks, manual edits are error-prone, and avoiding dependencies is impractical.

4. Final Answer:

   Run 'npm audit' regularly and update vulnerable packages -> Option A

5. Quick Check:

   Use npm audit and update often = Run 'npm audit' regularly and update vulnerable packages [OK]

Hint: Use npm audit and update packages regularly [OK]

Common Mistakes:

• Ignoring audit warnings
• Editing lock files manually
• Avoiding dependencies completely