If Your Site Still Uses Polyfill.io, It’s Now Phishing Your Customers
A critical credential-harvesting exploit is actively targeting websites that still load the hijacked, legacy polyfill.io script, tricking visitors with fake browser-level login prompts on trusted banking and e-commerce sites. Any credentials entered into this HTTP Basic Authentication box are sent directly to malicious actors, who also receive a header revealing exactly which website the user came from. While the original compatibility service was sold and weaponized in 2024, thousands of forgotten tags remain buried in website architectures; website owners must immediately audit their codebases and remove all references to polyfill.io to protect their users, while consumers should immediately close any unexpected login popups.