Front-End Development Security: Best Practices

In 2025, the importance of web security is obvious, however, what is web security? To significantly simplify it, let’s say web security is a multi-layered defense system protecting websites/web applications and, consequently, their users from digital threats. Web security consists of several important layers, each of which definitely deserves a separate article. However, as front-end development experts with a decade of experience, we’ve identified one critical layer of web security that is overlooked especially often. This layer is the front-end security.

Front-end or client-side security is a critical aspect of the entire web security system. It’s the alpha and omega of any security strategy. Despite its importance, it often gets less attention than its back-end counterpart. At the same time, neglecting the security on the front end is a risk most companies can’t afford. So, to shed some light on this topic, today we’ll explore front-end security best practices and see how they work in real-world scenarios. We’ll cover practical steps your product team can take to protect your web application and its users from the most common threats now. So, without further ado, let’s go!

A comprehensive look at front-end security

Web security is a complex field with many interconnected parts. Tech experts often divide web security into different sets of components, and there’s no one-size-fits-all approach regarding the division of web security. The way web security is categorized depends on your focus and goals. However, in today’s context, we will use the following simplified way to break down web application security:

What is front-end security?

Front-end web security is the practice of protecting the client-side of web applications. It focuses on safeguarding the code and data that runs in the user’s browser. This includes HTML, CSS, and JavaScript, as well as any assets loaded by the web page. In the context of our topic, the goal of security is to create a defensive barrier where the user interacts with the application. 

At its core, front-end cybersecurity deals with the principle of “never trust the client.” Since attackers can manipulate client-side code and data, developers must assume that any information sent from the browser may be malicious. This mindset shapes how security measures are implemented on the front-end, from input validation to protecting against cross-site scripting. It also influences how sensitive data is handled in browsers and how the front-end connects and communicates with the back-end. 

However, it’s a complex field that goes beyond just writing secure front-end code. Security of the front-end is all about understanding the common issues and vulnerabilities, best development practices, and how to implement them against these common issues and vulnerabilities. In practice, it basically means a deep understanding of the front-end development process, browser mechanics, web technologies, and how attackers can exploit them.

Why is front-end security important?

Here are the top 6 reasons why you should care about the security of front-end in your web application:

• User data protection: Security of the front-end safeguards sensitive user information entered through forms or stored in browsers. It’s the first line of defense that acts as the initial barrier against attacks;
• Reputation management: Secure front-ends build user trust. Investing in security protects your brand from the damage caused by security breaches;
• Compliance requirements: Many regulations, such as GDPR, require front-end security measures. Implementing these security measures just help you meet the legal obligations of your web app;
• Preventing client-side attacks: Well-tuned security stops threats like cross-site scripting (XSS) that target users directly;
• API protection: It helps secure communication between the front-end and back-end APIs;
• Reduced server load: By handling certain security checks on the client-side, you can decrease the burden on your servers.

Impact of insecure practices on business

We’ve seen why the security of front-end matters, but what happens when it’s overlooked? Well, data breaches and damage to reputation are the least you can expect. More often, it’s about the direct financial losses. Let’s look at several real-world cases of security failures.

Case#1: Let’s begin with the British Airways’ costly oversight. In 2018, a front-end attack hit British Airways hard. Hackers slipped malicious code into the front end of their website, siphoning sensitive personal and financial data from (!) 380,000 customers. The price tag? A staggering £183 million fine, not to mention the dent in their reputation

Case#2: Ticketmaster UK learned the hard way – twice. In 2018, a vulnerable third-party chatbot on their payment page led to a breach affecting 40,000 customers and a £1.25 million fine. It highlighted the risks of using external scripts without proper security vetting. The consequences of the second attack, the full scale of which remains unclear to this day, seem to be even more terrible.

Case#3: Macy’s online shoppers got an unwelcome surprise in 2019. A Magecart attack injected malicious code into the payment page, quietly stealing customer data for days. The fallout? A wave of distrust and a class-action lawsuit that’s still making headlines.

Common front-end security vulnerabilities

Now, let’s take a closer look at vulnerabilities, which are often used by malicious actors:

Cross-site scripting or XSS

This type of attack targets user input fields and dynamic page content. Attackers inject malicious scripts that run in users’ browsers. This can lead to data theft or unauthorized actions performed under the user’s identity. XSS attacks exploit the trust users have for a particular site.

Broken authentication

This vulnerability targets the very core of user access: login forms, session cookies, and authentication processes. Using weak password policies, poor session management, and flawed logic in authentication flows, attackers can gain unauthorized access to user accounts. This, in turn, can lead to identity theft, data breaches, or even large-scale attacks using automated tools to test stolen credentials across multiple sites. 

Clickjacking

Clickjacking, one of the most interesting techniques, manipulates the visual user interface of a website or web application. Attackers overlay invisible or disguised elements on legitimate buttons or links. Users inadvertently interact with malicious elements, leading to unintended actions or data submission. This attack can bypass users’ attention and security awareness, and that’s why it is considered one of the most dangerous techniques.

Client-side storage risks

This attack type targets browser storage mechanisms such as localStorage, sessionStorage, and cookies. Attackers can access, manipulate, or inject malicious data directly into client-side storage. As a result, this can lead to data theft, session hijacking, or persistent client-side malware.

Third-party library vulnerabilities

These vulnerabilities involve external JavaScript frameworks and libraries used for front-end development. Attackers exploit known vulnerabilities or inject malicious code into the dependencies. This can compromise the entire application’s security. 

DOM-based vulnerabilities

DOM-based vulnerabilities target dynamic page content manipulation through JavaScript. Attackers exploit unsafe coding practices when modifying the Document Object Model (DOM). This can lead to client-side script injection, data theft, or manipulation of page content and functionality.

Front-end security: Best Practices

Here are some of the most useful practices with specific steps to fortify your web applications against common attacks.

Input validation and sanitization: The very first line of defense

Always validate and sanitize user inputs on both the client and server sides. This practice helps prevent cross-site scripting attacks by removing or encoding potentially malicious code. It also guards against SQL injection and other input-based attacks. Implement strict input checks, use whitelists for permitted characters, and encode output to ensure data safety.

Content Security Policy: Controlling resource execution

Implement a strong Content Security Policy (CSP) to control which resources can be loaded and executed on your web pages. CSP helps mitigate XSS attacks and clickjacking by specifying trusted sources for scripts, styles, and other resources. It acts as a powerful second line of defense, limiting the damage even if potential attackers somehow manage to inject malicious content.

HTTPS everywhere: Securing data in transit

Use HTTPS for all communications between the browser and server. This HTTPS-based approach encrypts data in transit, primarily protecting against man-in-the-middle attacks and data interception. HTTPS also verifies your website’s identity, building trust with users. To implement ‘HTTPS everywhere’, make sure to redirect all HTTP traffic to HTTPS and use secure cookies as well.

Secure cookie management

Set appropriate security attributes for cookies to protect against the most common types of attacks. For instance, the ‘Secure’ flag ensures cookies are only transmitted over HTTPS (mentioned above). ‘HttpOnly’ prevents JavaScript access to cookies, guarding against potential XSS attacks. The ‘SameSite’ attribute helps prevent CSRF attacks by controlling cross-site cookie behavior. Also, check other flags. 

CORS: Managing cross-origin access

Properly configure Cross-Origin Resource Sharing (CORS) to control which domains can access your resources. CORS functions as a gatekeeper, ensuring that only trusted domains interact with your application’s resources. This configuration prevents unauthorized API access and protects against cross-origin attacks. To implement CORS, specify allowed origins precisely, avoiding wildcards. Also, carefully consider the implications of allowing credentials in cross-origin requests. 

Subresource integrity: Verifying external resources

Implement Subresource Integrity (SRI) for external scripts and stylesheets. SRI ensures resources hosted on third-party servers remain untampered. It works by specifying a cryptographic hash that fetched resources must match, protecting against compromised CDNs or third-party sources. This added layer of security is crucial in maintaining the integrity of your web application, especially when relying on external resources that may be beyond your direct control.

Security headers: Enhancing browser protection

Another practice that can bolster your website’s defenses is implementing security headers. For instance, X-Frame-Options prevents clickjacking, while X-XSS-Protection activates built-in XSS features, Strict-Transport-Security enforces HTTPS usage, ensuring encrypted connections, Content-Security-Policy allows you to specify trusted sources for content, mitigating XSS and data injection attacks, and eventually, Referrer-Policy controls how much referrer information should be included with requests. These headers add significant security layers with minimal implementation effort, providing a robust defense against common web vulnerabilities.

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Third-party library management

Regularly update and audit third-party libraries and dependencies. Outdated libraries can introduce known vulnerabilities to your application. Utilize automated tools to check for vulnerable dependencies and maintain an inventory of all third-party code. Then, carefully evaluate the security implications of new libraries before integrating them into your ecosystem. Implement a process for regular security reviews of your dependency tree. Also, stay informed about security advisories related to the libraries you use. Eventually, consider implementing a policy that requires approval for adding new dependencies to minimize unnecessary exposure.

Client-side storage security

Exercise caution with client-side data storage. First of all, avoid storing sensitive information in local or session storage, as these are accessible via JavaScript. For necessary client-side data, implement encryption before storage and secure retrieval mechanisms. Consider the risks associated with client-side storage in your overall security strategy. Using secure flags for cookies to prevent interception as mentioned above, can also be seen as a part of a client-side storage security strategy. Regularly audit and clean client-side storage to minimize data exposure. After all, educate your development team about the risks and best practices for client-side data handling.

Error handling of the front-end

Implement robust error handling on the front-end to prevent exposure of sensitive information. Use custom error pages and generic error messages to avoid information leakage that could aid attackers. While logging detailed errors securely on the server side for debugging, ensure this information is never exposed to users through the UI. Implement a centralized error-handling mechanism to ensure consistent error management across your application. Consider using error boundaries in frameworks like React to gracefully handle and contain errors. Regularly review and update your error-handling strategy to address new potential information leakage vectors.

Testing front-end application security

Testing the security in front-end applications is one of the most important points in the entire security strategy. This involves examining various aspects of web applications’ performance, including testing the performance of the practices mentioned above. Also, a good practice when checking the security of the front-end of your application can be simulating real-world attack scenarios. These simulations help you uncover weaknesses in your security strategies and adjust them as needed. 

Here, we also provided the list of three popular tools that can help your development team with security testing:

• OWASP ZAP (Zed Attack Proxy): An open-source, free-to-use tool that automatically finds various security vulnerabilities in web applications. We recommend using it for identifying issues like XSS and SQL injection in dynamic web applications.
• Burp Suite: A powerful platform for web application security testing that provides you with all the required tools for mapping, analysis, and exploitation of security flaws. Its proxy feature excels at intercepting and modifying web traffic, making it invaluable for manual testing and customized attack simulation.
• Acunetix: An automated web application security testing tool that detects and reports on a wide range of web vulnerabilities. Acunetix stands out for its comprehensive scanning capabilities, especially ifor detecting complex vulnerabilities like blind SQL injection and out-of-band XML external entity injection.

Integrating security into the development process

Building secure applications isn’t just about adjusting software at the final stage of the development process. “Shift left”  is a philosophy that brings security to the forefront, integrating it into every development stage. By adopting this philosophy and consequently prioritizing security from the outset, your development team can identify and address security vulnerabilities early, saving resources while bolstering user confidence.

1. Security training and awareness: Knowledge is power so, your first priority should be equipping your team with the tools and practices to recognize and address digital threats. Regular training sessions keep everyone updated on the latest security trends and best practices for addressing these threats. Foster a culture where security awareness becomes second nature, encouraging continuous learning and vigilance among all team members.
2. Threat modeling: Begin each project or major feature implementation with thorough threat modeling sessions. Identify potential security risks specific to your application’s architecture and use cases. Use these insights to guide development decisions and establish security requirements
3. Secure coding standards: Establish and enforce secure coding standards across your development team. Include guidelines for input validation, output encoding, and authentication. Implement a code review process that checks for adherence to these security standards.
4. Automated security testing: Integrate security testing tools into your CI/CD pipeline. Include static, dynamic, and composition analysis tools in your automated tests. Set up alerts for security issues detected during these automated checks.
5. Regular security audits: Conduct regular security audits of your application. Engage external experts for penetration testing to identify missed vulnerabilities. Use audit results to improve your security practices and update threat models.
6. Incident response planning: Develop and maintain an incident response plan for security breaches. Start by defining roles and responsibilities within the team for handling security incidents. Regularly practice and update this plan to ensure effective response to potential issues.

Looking for expert advice?

Looking to enhance your security strategy but not sure where to start? ELITEX’s team of experts can help you implement robust front-end security measures tailored to the specific needs of your business. Whether you’re looking for security experts with a strong front-end background to enhance your current workflow or seeking a development partner who can be trusted to bring your ideas to life, don’t hesitate to contact ELITEX. With ELITEX, you always receive results beyond initial expectations.

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