Over 100,000 websites fell victim to a recent web supply chain attack through the Polyfill JavaScript library. This incident underscores significant vulnerabilities in third-party script integration across the web. This article covers what Polyfill does, why it’s now a threat, and the steps you should take if your website relies on it.

The defense supply chain is a complex network of partners that sell, manufacture, and distribute services or products to defense agencies worldwide. It is made up of both major corporations and smaller sub-suppliers. Each country has its own network of supply chain partners, including manufacturers, software, services and logistics providers that deliver products and services for military materiel applications.

Polyfill.io helps web developers achieve cross-browser compatibility by automatically managing necessary polyfills. By adding a script tag to their HTML, developers can ensure that features like JavaScript functions, HTML5 elements, and various APIs work across different browsers. Originally developed by Andrew Betts, Polyfill.io injects JavaScript polyfill libraries based on the user agent or other characteristics, streamlining code maintenance.

Over 100,000 websites using a popular JavaScript service (polyfill.io) are now victims of a web supply chain attack. A web supply chain attack is a cyberattack is a type of software supply chain attack that targets a third-party web software component to gain access to an organization’s systems or data. These attacks can be difficult to prevent because they can be hard to detect, take advantage of trust, and have long-lasting effects.

For over a decade, a massive vulnerability that could have unleashed a huge supply chain attack lay dormant. Luckily the good guys found it first or so it seems. This month we are taking a look at CVE-2024-38368.

In the last decade, outsourcing to third parties–especially in the gig economy–has taken over key functions that enterprises used to handle internally. Today’s companies are frequently virtual–using third-party services that span the likes of application development, back-office corporate functions, contract manufacturing and research, marketing, and core IT services.

On June 24, 2024, cybersecurity company Sansec published a security advisory detailing how an associated Polyfill domain (cdn.polyfillio) was being used to insert malicious code in scripts served to mobile end users in a web supply chain attack. Polyfill is a popular open-source JavaScript library embedded in more than 100,000 websites to provide polyfills, a small piece of code (usually JavaScript) that helps provide modern functionality on older browsers.

Polyfill.js is a popular open-source project that provides modern functionality on older browsers that do not support it natively; users embed it using the cdn.polyfill.io domain. On February 24, 2024, a Chinese company named Funnull acquired both the domain and the Github account. Following that acquisition, the developer, Andrew Betts, tweeted on his X account a warning for all of his service’s users urging them to remove any reference to polyfill from their code.