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As a developer, you probably have a love/hate relationship with JavaScript. According to the 2023 Stack Overflow Developer Survey, JavaScript maintained its eleven-year winning streak as the commonly-used programming language, yet only 57.83% admired it while those who desired it dwindled to 40.15% of respondents. Sure, you use it. Sure, it’s been around a while. Unfortunately, it’s also susceptible to vulnerabilities. 

If you’re using it to program your web application, you can follow some basic secure-coding practices to mitigate JavaScript vulnerability risks. 

Why is JavaScript vulnerable?

Most developers who build applications using JavaScript for client-side personal information processing know they must be extra cautious about securing their code. As the most commonly used language, malicious actors target it because they know that finding a vulnerability gives them “bang for their buck.” By identifying a vulnerability, they can leverage it across many different applications. 

Additionally, as a front-end language, attackers can easily identify and exploit activities in the front-end application. Malicious actors can manipulate query strings by modifying the code in their browsers or sending direct server-side requests that bypass the front-end protections. 

Finally, JavaScript is an older programming language so it lacks the built-in security permissions model that newer languages include. Once a script executes on a user’s browser, it can perform various actions without requiring explicit user consent or control. 

JavaScript Security Issues and Risks

Since JavaScript isn’t going away any time soon, you should understand some key security issues so that you can protect your application against attacks. 

JS Source Code Vulnerabilities

Like every other programming language, JavaScript source code vulnerabilities can come from open-source packages and libraries. For example, in December 2022, malicious actors used typosquatting to trick developers into using packages that impersonated popular request libraries, poisoning the software supply chain

Unintended Script Execution

The Document Object Model (DOM) represents a web page’s structure, style, and content so that developers can manipulate the HTML source code. Attackers can modify the DOM in a victim’s browser, injecting malicious scripts as part of a DOM-based Cross-Site Scripting (XSS) attack

Exclusive Reliance on Client-Side Validation

Client-side validation gives the user feedback about the inputs they provide, like when they fill out a form. However, when you program the web application’s validation only for the user’s browser, attackers can send data to servers, corrupting records and configurations. 

Exposure of Session Data

Data transfers between the user’s browser and application server often include sensitive information, like user session ID. Malicious actors can access the communications between the browser and the application using client-side browser scripts. 

Unintentional User Activity

When malicious actors manipulate a person’s browser, they can impersonate the authenticated user. Combining this capability with other JavaScript security issues, they can inject and execute malicious code on the website. 

Steps to Mitigate JavaScript Vulnerability Risks

By implementing secure code best practices, you can mitigate data breach risks and protect user data more effectively. 

Use Trusted Third-Party Libraries and Plugins

When using open-source code, you should verify it to ensure it is a trusted resource. You should:

  • Read file names carefully to reduce typosquatting risks
  • Ensure the repository is maintained and updated regularly
  • Monitor for and apply security patches and updates

Identify and Audit Dependencies

You need visibility into not only the third-party resources that you use, but the fourth-party dependencies embedded in them. Using a Software Composition Analysis (SCA) tool enables you to identify all dependencies within your source code. 

Use a JavaScript Linter

Linters check your code for:

  • Programmatic error
  • Stylist errors
  • Excess indentation levels
  • Long functions
  • Wrong use of equality
  • Known vulnerabilities

Use Subresource Integrity (SRI)

SRI gives browsers a way to identify maliciously altered files. You should generate a hash value for external JavaScript files and add it to your HTML code so the SRI checking works, reducing risks arising from cross-origin requests.

Sanitize Output

When you sanitize the output, you prevent sensitive data from being sent to the client-side. You should ensure that you:

  • Strip all sensitive information from client-side communications
  • Send only the least amount of required information
  • Ensure general error message contain no sensitive data

Validate Referrer Headers

Servers check referred headers to ensure that the requests come from expected resources. Your application should reject all requests that do not have expected values. 

Quiet AI: Deep Code Analysis to Rapidly Detect JavaScript Vulnerabilities

Whether you love or hate JavaScript, you’re still using it, and code scanning can be time-consuming. Additionally, remediating vulnerabilities becomes overwhelming when you have to pick out the true risks from the false positives. 

Qwiet AI’s preZero platform enables you to identify and remediate your application’s most critical and impactful vulnerabilities. Our proprietary Code Property Graph (CPG) breaks code down into its fundamental parts while correlating them with data flows so that you can identify the vulnerabilities attackers are most capable of exploiting within your source code’s context. With Qwiet Blacklight, the only threat intelligence feed focused on application security, you gain visibility into real-world attacks actively targeting vulnerabilities, enabling you to enhance your prioritization strategies. 


Try Qwiet AI’s preZero platform for free to see how it can help you mitigate JavaScript vulnerabilities and speed time-to-market.

About ShiftLeft

ShiftLeft empowers developers and AppSec teams to dramatically reduce risk by quickly finding and fixing the vulnerabilities most likely to reach their applications and ignoring reported vulnerabilities that pose little risk. Industry-leading accuracy allows developers to focus on security fixes that matter and improve code velocity while enabling AppSec engineers to shift security left.

A unified code security platform, ShiftLeft CORE scans for attack context across custom code, APIs, OSS, containers, internal microservices, and first-party business logic by combining results of the company’s and Intelligent Software Composition Analysis (SCA). Using its unique graph database that combines code attributes and analyzes actual attack paths based on real application architecture, ShiftLeft then provides detailed guidance on risk remediation within existing development workflows and tooling. Teams that use ShiftLeft ship more secure code, faster. Backed by SYN Ventures, Bain Capital Ventures, Blackstone, Mayfield, Thomvest Ventures, and SineWave Ventures, ShiftLeft is based in Santa Clara, California. For information, visit:


See for yourself – run a scan on your code right now