In AppSealing News, AppSealing Blog

JavaScript is one of the most popular programming languages used by developers around the world for web and mobile app development. According to a survey, 67 percent of web developers prefer to use JavaScript and it is used in over 95 percent of websites. 

But when we consider it from a security point of view, JavaScript is fourth on the list of most vulnerable languages, right below Java, C, and PHP. That is why it is crucial for developers to ensure javascript protection while developing and maintaining JavaScript applications. 

In this article, we will discuss the main principles of JavaScript security, common JavaScript vulnerabilities, and how to deal with those vulnerabilities.

JavaScript Security

JavaScript is one of the most fundamental technologies used for building web applications, mobile applications, and server-side applications. But its popularity has also made it a big target for hackers.

Common JavaScript Vulnerabilities

Cross-site scripting (XSS)

One of the most common browser-side vulnerabilities for JavaScript is Cross-Site Scripting (XSS) in which attacks occur when an outside hacker successfully injects malicious code into a vulnerable application. According to a recent study, 40 percent of all cyberattacks are XSS attacks.

The attackers can manipulate both HTML and JavaScript in order to trigger malicious code. With XSS, the vulnerable website or application works as the main vehicle to execute the malicious code on the user side.  

It is important to note that XSS is a highly rated security vulnerability because the attacker can easily get access to SessionStorage, LocalStorage, and even cookies. As a result, to protect your JavaScript applications against XSS, you should never inject any unknown scripts into the web page and always use CSS escape.

The Reserve Bank in New Zealand was the victim of a recent hack where personal and commercial bank data was compromised due to XSS vulnerabilities.

Cross-Site Request Forgery (CSRF)

In Cross-Site Request Forgery or CSRF attacks, a user’s session cookie is hijacked in order to impersonate their browser session. With CSRF, attackers can easily trick users into executing malicious code or taking unauthorized actions on the website or the application.  

 The most common way of initiating a CSRF attack is by finding all the unprotected form elements present on a web page and injecting malicious code through it. Hackers can use CSRF to update the email address of a user on the website and then request a password change in order to take over their account. To avoid this, developers should add a CSRF token to all the forms on their website. 

Glassdoor was found to have a site-wide CSRF bug of a 9-10 severity score. The vulnerability, if exploited, could give hackers access and editing permissions to jobseeker profiles and employer accounts. Luckily this vulnerability was discovered by a bug bounty researcher and quickly fixed by the company before it could lead to any damage.

Server-Side JavaScript Injection

This is a considerably newer type of JavaScript vulnerability, which is why it often gets ignored by developers. With Server-Side JavaScript Injection, the hacker can upload and execute malicious code with binary files onto the webserver. Executed on the server level, it majorly targets NoSQL and Node.JS applications, and it can severely affect the website.  

Orbit Fox is a multi-featured WordPress plugin which works with Gutenberg and Elementor to add site-building capabilities. Used and installed by over 400,000 websites, it was found to have two major vulnerabilities that could allow hackers to inject malicious code in the websites that had the plugin installed and take control of them.

Client-Side Issues

When developers introduce outside API on the client-side, it can often make the application more vulnerable to outside attacks. In cases like these, poor web development practices are usually to blame. Moreover, client-side browser scripts have access to all the content that is returned by the web app directly to the web browser which can include cookies with sensitive data like user session IDs. This can in turn lead to hackers trying to hijack user sessions and probe for sensitive user data. 

Dealing with JavaScript Protection Issues

The biggest advantage of using JavaScript is that it comes with numerous open-source packages which make the development process a whole lot easier and faster. But these packages also introduce a lot of vulnerabilities which can give hackers an opportunity to steal or compromise user data. The best way to protect your applications from JavaScript vulnerabilities is by always following the recommended best practices and using sophisticated JavaScript analyzers that can effectively detect issues and vulnerabilities in your code. 

Here are a few tips you can follow to better secure your JavaScript applications:

Adopt Runtime Application Self-Protection (RASP)

Runtime Application Self-Protection is a technology which is designed specifically to detect attacks on an application in real-time. It analyzes both the app’s behavior and the overall context of the behavior in order to protect it from any malicious attacks. Since RASP continuously monitors the app’s own behavior, it becomes easier to identify and mitigate any issues in real-time without any manual human intervention.

Avoid using the eval() function

The eval() function is mostly used by developers to run their text as a piece of code which by itself is a bad coding practice. It can make your JavaScript application open to attacks and increase the risk of vulnerabilities. As a result, you should avoid using it as much as possible and replace it instead with more secure functions. 

Encrypt with SSL/ HTTPS

Encrypt data on the client and the server-side to make your application more secure. That means, even if hackers get access to your data, it will be in encrypted form and unusable to them. At the same time, you should also set the cookies as secure to limit the use of your application cookies to secure and encrypted website pages only. 

Focus on API Security

While developing JavaScript-based applications, it is important to focus on API security as well. You can start by securing API keys in client-side JavaScript applications and restricting access to particular IP ranges.

Top JavaScript Security Analyzers

JavaScript security analyzers are security tools that can help you examine your website or application from the inside in order to determine if it is vulnerable to attackers or malicious code injections. 

Here are some of the vulnerability scanning tools that you could use


Developed by security authority OWASP, ZAP, or Zed Attack Proxy can scan your website for numerous vulnerabilities at the same time. It can be customized according to your requirements and it offers an easy to use intuitive interface.


Grabber is another JavaScript security analyzer which can scan both websites and web applications for vulnerabilities like XSS, SQL injection, and file inclusion. It is a considerably small application run on 2.5kLOC in Python which is why it is more suitable for small applications and websites


With Wapiti, you can test attack as well as injection vectors by using POST HTTP and GET Requests. It can detect file inclusion, file disclosure, weak apache configurations, XSS attacks, and more. It is important to note that this is an advanced tool that needs to be executed through the command line

Identifying the potential JavaScript security problems is the first step towards securing your application and business data. Take a proactive approach to security and actively look for vulnerabilities before deploying the code to ensure your application is always safe and you are able to offer the end-users the best experience possible.

Govindraj Basatwar, Global Business Head
Govindraj Basatwar, Global Business Head
A Techo-Commerical evangelist who create, develop, and execute a clear vision for teams. Successfully created a SaaS business model with multi Million Dollar revenues globally. Proven leadership track record of establishing foreign companies in India with market entering strategy, business plan, sales, and business development activities.