Re: [whatwg/fetch] From-Origin (#687)

The iframe element doesn’t emit load errors. Instead, it loads empty and fires onload. I believe it’s an old security discussion where the “arbitrary load” capabilities of iframes and their ability to synthesize documents out of non-document responses were considered dangerous if an attacker can use onload/onerror to test for resource existence, perform multi step CSRF, or check victim privileges. Maybe someone else in this thread knows more?

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