Outdated JavaScript Libraries: Why Old Dependencies Are a Security Risk

Why Old JavaScript Libraries Are a Security Problem

JavaScript libraries are the building blocks of the modern web. jQuery, Bootstrap, Lodash, Moment.js — millions of sites depend on them. But every library has a version history, and older versions often contain known vulnerabilities with published exploits.

When you load an outdated library, you're potentially running code with known security holes. Attackers actively scan for sites using vulnerable library versions because the exploit work is already done for them.

When WebSentry scans your site, the JavaScript libraries check identifies libraries loaded on your page and flags versions with known vulnerabilities.

How Vulnerable Libraries Get Exploited

The most common attack is Cross-Site Scripting (XSS) through library vulnerabilities. Older versions of jQuery, for example, had several XSS vulnerabilities where passing user-controlled input to certain jQuery methods could execute arbitrary JavaScript.

CVE-2019-11358 affected jQuery versions before 3.4.0. A site running jQuery 1.x or 2.x was vulnerable to prototype pollution attacks that could escalate to XSS depending on how the library was used.

The Most Commonly Outdated Libraries

jQuery

jQuery 1.x and 2.x are end-of-life and contain multiple known vulnerabilities. Many sites still load them because they were bundled years ago and never updated. jQuery 3.7+ is the current supported branch.

Bootstrap

Bootstrap versions before 4.3.1 contained XSS vulnerabilities. Bootstrap 3.x is end-of-life. If you're loading it from a CDN link in your HTML, update the version number in the URL.

Lodash

Versions before 4.17.21 had prototype pollution vulnerabilities (CVE-2021-23337).

How to Find and Update Outdated Libraries

For npm-managed projects

npm audit
npm audit fix
npm outdated

For CDN-loaded libraries

Replace pinned version URLs with the latest and add a Subresource Integrity hash:

<script
  src="https://code.jquery.com/jquery-3.7.1.min.js"
  integrity="sha384-1H217gwSVyLSIfaLxHbE7dRb3v4mYCKbpQvzx0cegeju1MVsGrX5xXxAvs/HgeFs"
  crossorigin="anonymous">
</script>

Staying on Top of Library Security

• Dependabot / Renovate: Enable these GitHub tools to automatically open PRs when dependencies have vulnerabilities
• npm audit in CI: Add npm audit --audit-level=high to your build pipeline
• Regular scans: Re-run a WebSentry scan after updates to confirm vulnerable versions are gone

Summary

Outdated JavaScript libraries are one of the most common and preventable security risks on the web. The fix is usually a version number change. Make dependency updates a routine part of your development process and re-scan regularly.