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You’ve probably heard of CORS, but did you know about CORB, CORP, COOP, or COEP?

I recently watched “A Hipster History of CORS”, a talk from Strange Loop 2022 by Devdatta Akhawe, Head of Security at Figma. Devdatta does a great job of taking a complex, even boring, subject like CORS and weaves it into a funny, interesting narrative history. He connected many previously disparate dots in my head, making me go “Ah-ha! That’s why things are the way they are on the web.”

For example, when working on my Readlists project, I ran into an issue where I couldn’t use JavaScript to read the contents of an image fetched from a third-party website. I couldn’t understand why there was a limitation there. “I fetch images all the time with <img src="..."> but I guess JavaScript’s not gonna let me?”

After Devdatta’s talk and an introduction to cross origin read blocking (CORB) I now understand better.

[attacker.com can ask for mail.google.com] as an image. The browser doesn’t know that's not an image. For the browser, everything is a URI. So the browser [fill fetch it] and say “here’s mail.google.com (and everything in the body)” and the attacker.com process can just read everything in it.

It’s a great story condensed into a thirty minute talk. Thank you Devdatta!