/jan 8, 2024

Securing JavaScript: Best Practices and Common Vulnerabilities

By Jenny Buckingham

JavaScript is the most commonly-used programming language, according to the most recent StackOverflow developer survey. While JavaScript offers great flexibility and ease of use, it also introduces security risks that can be exploited by attackers. In this blog, we will explore vulnerabilities in JavaScript, best practices to secure your code, and tools to prevent attacks.


Understanding JavaScript Vulnerabilities 

If you're short on time, you can begin by using Veracode DAST Essentials, a JavaScript security scanner, to identify potential vulnerabilities. Running this tool will quickly generate reports, highlight your specific vulnerabilities, and provide clear instructions on how to remediate them. 

JavaScript Source Code Vulnerabilities

JavaScript developers typically rely on integrating numerous public or open-source packages and libraries containing hidden vulnerabilities and exposing security issues within the source code. Open-source vulnerabilities might not be easily recognizable at first, and using a vulnerable package expands the attack surface of your web app.

Unintended Script Execution

JavaScript embeds functions on HTML web pages when interacting with a web page’s Document Object Model (DOM). Attackers can embed scripts into these functions, then execute them by all client computers that connect to the web page. 

Exclusive Reliance on Client-Side Validation

Relying solely on client-side validation leaves room for hackers to send unverified data to servers, compromising records and configurations. Implement server-side validation for enhanced security.

Exposure of Session Data

Attackers leverage the power of client-side browser scripts to access all communication between the browser and the web application. This communication may include sensitive session data, such as user session IDs used for unauthorized access.

Unintentional User Activity

Attackers may use several techniques that manipulate a browser into performing malicious activities on various websites users are already logged on to. Additionally, hackers take advantage of JavaScript security gaps that execute threat vectors on other sites in the background as soon as a browser is logged in.


JavaScript Security Risks You Should Know About

Attackers commonly use well-known JavaScript security vulnerabilities to navigate through security loopholes of an application’s attack surface to compromise user and system data. As a result, they often show up in a security audit report generated by a security scanner.

These common vulnerabilities include:

Cross-site Scripting Vulnerabilities

Cross-Site Scripting vulnerabilities (XXS) involve a code javascript injection attack from the client side. Where hackers embed malicious scripts on legitimate web pages, the application passes unvalidated data to web browsers. Web applications that factor in unfiltered user input in the generated outputs are most susceptible to Cross-Site Scripting attacks. XSS common attacks or potential vulnerabilities can be prevented through:

  • Filtering & sanitizing user input
  • Using effective response headers
  • Encode data before output generation
  • Utilize Content Security Policies
  • Using regularly an XSS Scanner before every release

Cross-site Request Forgery Vulnerabilities

Cross-Site Request Forgery (CSRF) is a widespread security vulnerability in which threat actors manipulate legitimate users into submitting malicious requests to web applications they are ambushed to visit. When the web application fails to differentiate between valid user requests and forged requests, attackers can execute any malicious actions under the guise of legitimate end-users. 

CSRF attacks can be prevented by:

  • Implementing secure random tokens
  • Logging off unused web applications
  • Disallowing automatic password entries by browsers
  • Securing session credentials
  • Using regularly a CSRF Scanner before every release

Server-side JavaScript Injection Attacks

This mechanism injects and executes malicious or arbitrary code on a web application’s server without sanitizing and filtering user inputs. Attackers typically look for functions that parse user-generated data without proper validations to ingest insecure scripts to be executed by the server. 

Server-side JavaScript injection attacks are typically prevented by properly validating and filtering user inputs.


Best Practices to Secure JavaScript Applications

Avoid Evaluating User Input: The eval() and new Function () command executes arguments passed in user inputs as JS expressions. As hackers manipulate user input to run malicious scripts, it is recommended to avoid evaluating user inputs or parsing JSON data through the above constructors.

Enable TLS/SSL Encryption: Encrypting data between servers and clients helps prevent CSRF and XSS attacks.

Secure API Access: It is essential to assign tokens for each user accessing the web app through the API, enabling secure access.

Set Secure Cookies: By setting cookies as secure, each cookie can only be used for a single web page, ensuring encrypted access.

Define Content Security Policies: Content security policies ensure that attackers don’t inject malicious scripts into web applications to manipulate state changes.

Run a JavaScript Security Scanner: Use a JavaScript security scanner to identify vulnerabilities like XSS, CSRF, and injection attacks. This provides a continuous security approach by running regular probes on your staging system.


Securing JavaScript with Veracode

Securing JavaScript code is crucial for protecting web applications from attacks. By understanding the common vulnerabilities, implementing best practices, and using reliable security scanning tools, you can enhance the security of your JavaScript applications. 

Veracode Dynamic Analysis (DAST) is a trusted solution used by software vendors and organizations worldwide to deploy safer web applications. With its collection of JavaScript scanning mechanisms, it enables comprehensive vulnerability assessments for APIs, web applications, and microservices, with a low false positive rate. Integrated with modern development stacks, Dynamic Analysis reduces the risk of API and web application hacks. Additionally, it provides downloadable security audit reports for easy sharing with your team or clients.

Start your 14-day free trial of Veracode's DAST solution today and discover how Veracode can help you detect, investigate, prevent, and remediate JavaScript vulnerabilities, enhancing the the security of your modern applications. Additionally, here is a comprehensive guide that dives deeper into common vulnerabilities in JavaScript applications, their types, organizational impacts, and effective mitigation strategies.



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By Jenny Buckingham

Jenny Buckingham is a Product Marketing Manager helping developers and security professionals secure their cloud-native application development. With a focus on understanding her customer’s needs, she helps companies leverage powerful solutions to overcome security challenges.