I worked 2012-2016 for a big telco company in my country and there was this HTTPS webpage with an iframe rendering any url you passed over the ?url query param plus a header with the company's logo.

I was on a meeting with some friends in charge of social media and they found it for a user report.

Unbelievable 🤷🏻‍♂️ I remember I tried the page's url itself and it rendered a loop of the header with the company's logo 😂