Automatically replacing polyfill.io links with Cloudflare’s mirror for a safer Internet

polyfill.io, a popular JavaScript library service, can no longer be trusted and should be removed from websites.
Multiple reports, corroborated with data seen by our own client-side security system, Page Shield, have shown that the polyfill service was being used, and could be used again, to inject malicious JavaScript code into users’ browsers. This is a real threat to the Internet at large given the popularity of this library.
We have, over the last 24 hours, released an automatic JavaScript URL rewriting service that will rewrite any link to polyfill.io found in a website proxied by Cloudflare to a link to our mirror under cdnjs. This will avoid breaking site functionality while mitigating the risk of a supply chain attack.
Any website on the free plan has this feature automatically activated now. Websites on any paid plan can turn on this feature with a single click.

You can find this new feature under Security ⇒ Settings on any zone using Cloudflare.
Contrary to what is stated on the polyfill.io website, Cloudflare has never recommended the polyfill.io service or authorized their use of Cloudflare’s name on their website. We have asked them to remove the Continue reading



