> I wouldn't call this "known security issues", it's an inherent problem with any signup or forgot password page.

It's not inherent, though! Easy, definite fix: Reverse the communication relation. If the user has to open their mail app anyway, you could simply require them to send an email to you, instead of vice versa. This would solve the problem completely. (If spoofing the sender could be done reliably, the service wouldn't be involved in the first place.)

Now, it would slightly increase friction and lower convenience. That's why it's not done. It's inherently incompatible with dark patterns, data collection and questionable new user acquisition, but this too could be solved through standards and integration - without making Cloudflare de facto infrastructure necessity!

Possible convenient, better solutions: Have the browser send this mail, either by passing a template to the mail app, integrating SMTP into the browser/addon, or instate a novel authentication protocol, which in fact may remove the human interaction completely.

As if 2FA security was the main motivation for asking for email, and/or phone anyway. Companies want user IDs, if possible UIDs, as soon as possible to increase user data value and gain marketing opportunities. I once had a "welcome mail" after typing in the address, before sending the form. Yeah...

But cloudflare is also just difficult, I’m on Starlink (because where I am my only other option is Hughes net), and my browser of choice is Safari. No vpn, and only boring ad blockers.

I routinely blocked by Cloudflare from viewing things and occasionally, I am blocked from buying things. Just this weekend, it was $100 worth of athletic wear. I just keep clicking the box and it never lets me complete the purchase. After the 7th or 10th time I go and find another vendor that would actually sell to me. I was more annoyed than usual because the website already had my credit card at this point – but as this article proves there are reasons to block an order even with a credit card.

Cloudflare is becoming a single point of failure. That is not a solution.

And these people weren't validating the email address on signup. To "reduce friction" i guess.

Cloudflare is not the solution

Op basically said that the firewall rules and email confirmation alone would've mostly mitigated this.

But also Anubis is a good alternative to slow bots.

How about a signup flow where the user sends the first email? They send an email to signups@example.com (or to a generated unique address), and receive a one-time sign-in link in the reply. The service would have to be careful not to process spoofed emails though.

Another approach is to not ask for an email address at all, like here on HN.

Then you're not using any of their services besides DNS, at which point you don't need to use Cloudflare at all.

As soon as you turn on any other service they offer, you need to actively migrate away. It's an inherent issue of services that actually provide a benefit. If you're saying "I can just migrate to any other nameserver" then you're telling me you have no use for Cloudflare in the first place. Because if you did, you couldn't just not use it anymore.

Let's say you're using their WAF. Sure, you can just change your domain's nameserver and you've migrated away. But now you no longer have a WAF. Same for their CDN. Or their load balancer. Or their object storage. Or their CAPTCHAs.