12 Security Tips for Front-End Apps

Front-end apps are interactive applications that run on a user’s browser and are built using technologies such as HTML, CSS, and JavaScript or frameworks like React, Angular, or Vue. These apps are essential for creating engaging web experiences, but they also face security risks that can compromise their functionality and integrity.

In this blog post, we will explore common threats and vulnerabilities that front-end apps encounter and provide practical tips on how to improve their security and prevent hacking attacks.

Importance of Securing Front-End Apps

It is essential to secure your front-end app from various threats and vulnerabilities that can compromise its integrity and reliability.

• Front-end apps handle sensitive data such as personal information, payment details, health records, or login credentials. If these data are exposed or stolen by hackers, it can result in:
  • Identity theft
  • Fraud
  • Reputation damage
  • Legal liability
• Front-end apps can also affect the functionality and performance of your website or web application. Hackers can inject malicious code into your front-end app to:
  • Redirect your users to phishing sites
  • Display unwanted ads
  • Mine cryptocurrencies
  • Sabotage your business logic

In this article, we’ll explore a range of security concerns that can impact front-end applications, including various types of attacks, as well as strategies for preventing them. So, let’s jump right in and get started.

1) User Input Validation: A Key Step to Prevent Attacks

One of the most important security tips for frontend developers is to use strict user input validation. This means that you should check and sanitize the data that users enter in your app, such as forms, URLs, or cookies, before sending it to the backend or rendering it on the screen. This can help prevent common attacks such as cross-site scripting (XSS), SQL injection, or clickjacking.

There are different ways to implement user input validation depending on your technology stack and framework. For example, you can use built-in HTML attributes such as required, pattern, or maxlength to specify some basic rules for your input fields. 

You can also use JavaScript libraries such as validator.js or joi to perform more complex validations on the client-side. However, you should always remember that client-side validation is not enough and you should also validate user input on the server-side.

Here is a simple code example of how to use validator.js to validate an email address input field:

// Import validator.js library
const validator = require("validator");

// Get the email input value
const emailInput = document.getElementById("email").value;

// Check if the email is valid
if (validator.isEmail(emailInput)) {
  // Email is valid, proceed with submission
} else {
  // Email is invalid, show an error message
}

This code example demonstrates how to use the validator.js library to validate user input for email addresses. The isEmail method checks if the email input is valid, and if it is, the application can proceed with submission.

If the input is invalid, the application will display an error message. Validating user input can protect against potential vulnerabilities and attacks.

Another important consideration in frontend app security is data sanitization. Developers must ensure that all user-provided data is sanitized to prevent malicious code injections or other security breaches.

2) Beware of Hidden Fields or Data Stored in Browser Memory

Hidden fields type=”hidden” or data stored in browser memory localStorage, sessionStorage, cookies can be accessed by an attacker using tools like developer tools or web inspector.

To prevent this, you should encrypt or hash any sensitive data before storing it in hidden fields or browser memory.

You should also avoid storing sensitive data in cookies or local storage, as they can be easily read by an attacker.

Hidden Fields Example:

Let’s say you have a form on your website that asks users to enter their username and password. To maintain the user’s state between requests, you decide to store the user’s ID in a hidden field. However, an attacker could use browser developer tools to modify the hidden field and enter a different user’s ID, gaining access to their account.

Browser Memory Data Example:

Let’s say your website uses a JavaScript library to process credit card payments. The library stores the credit card number in the browser’s memory while the payment is being processed. However, an attacker could use a memory dumping tool to extract the credit card number from the browser’s memory, potentially exposing the user’s sensitive information. To mitigate this risk, you could use a more secure payment processing method that does not store the credit card information in the browser’s memory, or encrypt the credit card information before storing it in the memory.

3) Disable iframe Embedding

Disabling iframe embedding can protect us from clickjacking attacks. The “X-Frame-Options”: “DENY” header is one way to do that.

Another way is to use the frame-ancestors CSP directive, which lets us specify which websites can embed our website in an iframe.

4) Use a Strong Content Security Policy (CSP)

A Content Security Policy (CSP) is a way to enhance the security of your website by restricting how resources such as JavaScript, CSS, images, etc. can be loaded and from which URLs they can be loaded. A CSP is specified by adding a Content-Security-Policy header in your HTTP response.

For example:

Content-Security-Policy: default-src 'self'; img-src *; media-src media1.com media2.com; script-src userscripts.example.com

This header tells the browser that by default, content is only allowed from the same origin as the website, except for: Images can be loaded from any origin (note the “*” wildcard).

Media can be loaded only from media1.com and media2.com (and not from their subdomains).
Scripts can be executed only from userscripts.example.com.

A CSP can help protect your website from cross-site scripting attacks (XSS), which are a type of malicious attack where an attacker injects code into your website that runs in the browser of your visitors. By limiting where resources can be loaded from, you can prevent attackers from injecting malicious code into your website.

While a strong content security policy can reduce the risk of XSS attacks, it doesn’t completely solve the issue of inline script execution, which can still leave a vulnerability for XSS attacks.

5) Enable XSS Protection Mode

XSS Protection Mode is a browser feature that stops XSS attacks. XSS attacks are when attackers inject code into your website that runs in your visitors’ browsers.

You can enable XSS Protection Mode by adding a X-XSS-Protection header in your HTTP response.
The header has four values:

• 0: This value disables XSS Protection Mode. This is not recommended unless you have other ways to prevent XSS attacks on your website.
• 1: This value enables XSS Protection Mode. If the browser detects an attack, it will sanitize the page (remove the unsafe parts).
• 1; mode=block: This value enables XSS Protection Mode. If the browser detects an attack, it will not render the page at all.
• 1; report=<reporting-uri>: This value enables XSS Protection Mode and sends a report to a chosen URI when an attack is detected. This was a Chromium function.

The syntax for adding the header depends on your web server.

6) Avoid Typical XSS Mistakes

To prevent XSS attacks, avoid using innerHTML and instead use textContent in web applications. Be cautious when using dangerouslySetInnerHTML in React.

Suppose you have a website that displays a welcome message to the user based on their name from the query string. For example, if the URL is https://example.com?name=Bob, the website should display Hello, Bob!.

A naive way to implement this feature is to use innerHTML like this:

// Get the name from the query string
var name = new URLSearchParams(window.location.search).get("name");

// Set the welcome message using innerHTML
document.querySelector(".welcome").innerHTML = "Hello, " + name + "!";

However, this code is vulnerable to XSS attacks because an attacker can inject malicious code into the name parameter. For example, if the URL is https://example.com?name=<script>alert('XSS')</script>, the website will execute the script and display an alert box.

A better way to implement this feature is to use textContent like this:

// Get the name from the query string
var name = new URLSearchParams(window.location.search).get("name");

// Set the welcome message using textContent
document.querySelector(".welcome").textContent = "Hello, " + name + "!";

This code is not vulnerable to XSS attacks because textContent does not parse HTML tags or JavaScript code. It simply displays them as plain text. For example, if the URL is https://example.com?name=<script>alert('XSS')</script>, the website will display Hello, <script>alert('XSS')</script>! without executing anything.

I hope this code example helps you understand how to use textContent instead of innerHTML to prevent XSS attacks.

Use the latest version of web application frameworks and libraries to take advantage of built-in security features and updates. Regularly review your web application’s security measures to ensure you’re taking all necessary precautions.

Also, set the correct values for Content-Type and X-Content-Type-Options HTTP response headers to prevent accidental execution of malicious code. Avoid encoding JSON data as text/HTML.

7) Use ambiguous errors to protect user data

Instead of specific error messages like “Your password is incorrect,” it’s better to use ambiguous ones like “Incorrect login information” to prevent attackers from gaining helpful information.

// Bad practice: specific error message
if (password !== storedPassword) {
  showError("Your password is incorrect.");
}

// Better practice: ambiguous error message
if (password !== storedPassword) {
  showError("Incorrect login information.");
}

8) Use Captcha

Using Captcha at public-facing endpoints (login, registration, contact). A Captcha is a computer program or system intended to distinguish humans from bots and can help stop DoS (Denial Of Service) attacks.

9) Always Set Referrer-Policy

To prevent destination websites from accessing sensitive data like session tokens and database IDs, it’s important to use the “Referrer-Policy” header with a value of “no-referrer” so, whenever using anchor tags or links that navigate away from the current website.

Additionally, for anchor tags, the rel attribute can be set to “noopener” or “noreferrer” for added security.

<meta name="referrer" content="no-referrer-when-downgrade" />;

10) Restrict Access to Browser Features and APIs

To ensure limited access to browser features and APIs in frontend apps, we can use a Feature-Policy header. This allows us to deny access to certain features and APIs, such as Autoplay, camera, document write, geolocation, Fullscreen, and payment.

The Feature-Policy header has two parts: the directive, which is the feature you’re setting the policy on, and the allowlist, which specifies how the feature can be used. The allowlist can have one or more values, such as *, self, src, none, or origin(s).

To use Feature Policy, we can send an HTTP header, either for the entire site at the web server level or from the application. For example, to prevent the use of the geolocation API, we can add the following header:

add_header Feature-Policy “geolocation none;”;

Multiple policies can be set in a single header, like this:

add_header Feature-Policy “vibrate none; geolocation none; unsized-media https://example.com;”;

If we’re primarily concerned with the content in an iframe, we can use Feature Policy on the iframe itself, using the allow attribute. This allows us to prevent the use of certain APIs within the iframe, such as geolocation, camera, and microphone APIs.

11) Audit Dependencies Frequently

Run npm audit regularly to get a list of vulnerable packages and upgrade them to avoid security issues. GitHub now flags vulnerable dependencies. We can also use Snyk that checks your source code automatically and opens pull requests to bump versions.

12) Third-Party Services: Use Them Wisely

Some third-party services like Google Analytics or Intercom can make your web app less secure. If they get hacked, your app can get hacked too.

Use CSP policy to limit what they can do. Use integrity attribute to check if the script is safe.

<script src= "https://example.com/example-framework.js" integrity= "sha384-oqVuAfXRKap7fdgcCY5uykM6+R9GqQ8K/ux..." crossorigin= "anonymous" ></script>

Watch Out for Autofill Fields

Autofill fields can save your personal information in the browser. But they can also leak your information to hackers.

Hackers can use third-party scripts to steal your email address and track your online activity. They can sell your data to the bad guys. Don’t use autofill for sensitive data.

🔒🚨💻 In conclusion, securing front-end apps is crucial in today’s digital landscape. With the increasing number of cyber threats, it’s important to implement strong security measures to protect your users’ sensitive information. By following these 12 security tips, you can significantly reduce the risk of data breaches and ensure your app’s security is top-notch. Remember to stay vigilant and keep up-to-date with the latest security best practices to keep your front-end app safe and secure! 🛡️💪

I hope you found this blog post helpful and informative. If you have any questions or feedback, please leave a comment below. Thank you for reading!

Additional resources related to security for front-end apps that you may find helpful:

• Frontend security primer – Frontend Mastery: A comprehensive guide on front-end security concepts and best practices.
• What Is Front-End Security? – Feroot: An introduction to front-end security and why it matters for businesses and customers.