This is a WordPress Plugin, released under the MIT license.
WordPress currently (as of WP 5.4.1) ships a very old quite deprecated version of jQuery, jQuery 1.12.4 which was released on . Even at the time, a large percentage of jQuery developers if not the majority had already moved to jQuery 2 and jQuery 3 was released soon after.
The jQuery 1 and jQuery 2 branches are no longer maintained. Security fixes have to be custom patched into the version that WordPress ships, which I believe they do, but whether it happens in a timely manner or not is debated.
Part of the reason WordPress ships with such an old version of jQuery is that some plugins and themes might break with a more modern version of jQuery resulting in users that do not upgrade WordPress to avoid the breakage.
A better approach is to fix what breaks, though if a plugin or theme maintainer does not do it, many users do not have the skill to take that approach.
At Pipfrosch Press, we do not want an ancient version of jQuery used for our front end so we developed a simple plugin that not only updates jQuery to the current version, but it also allows the current version of jQuery to be retrieved securely and robustly from a Content Distribution Network (CDN) improving the page load performance.
This plugin in now available through the standard WordPress plugin distribution channel: https://wordpress.org/plugins/pipfrosch-jquery/
The plugin also provides jQuery Migrate for backwards compatibility with scripts written for jQuery as old as 1.9 and thus has support for scripts written for the version of jQuery that ships with WordPress.