So, there is no way to handle this at the MySQL configuration level to disable this behavior of turning special characters into "normal" characters?

MYSQL will translate special characters back to normal characters automatically. So if I try to login as ⓣⓔⓢⓣ@ⓛⓐⓡⓐⓥⓔⓛ.ⓒⓞⓜ, once I reach the database, the special characters are read as normal characters, no matter if the field data is using special characters or not. Both versions equal the same.

However, when you're checking the number of requests in the throttle. PHP sees the special character key I've generated differently from the alphanumeric key. Resetting the throttle requests. That means an attacker can automate a brute force attempted by simply replacing a single letter with its special character counterpart after a certain number of attempts, bypassing the minute lockdown.

@taylorotwell

This character conversion can be done via https://github.com/voku/portable-ascii php package (already present in framework core)

use voku\helper\ASCII;

ASCII::to_transliterate("ⓐ"); // a
ASCII::to_transliterate("⓴"); // 20

I would suggest to introduce a helper in core like Str::transliterate() and use that helper in UI package.
This will keep UI package light and maintainable :)

@liamh101 Thought?

@ankurk91 @taylorotwell I'm happy to investigate/add this in. I'm not particularly proud of my current implementation as it's a bit messy, so this would be a good refinement.

I suggest we keep this in for now though for security reasons.

PR to core change: laravel/framework#40681

I assume this attack vector also applies to Fortify? Specifically the \Laravel\Fortify\LoginRateLimiter::throttleKey() method:

protected function throttleKey(Request $request)
{
    return Str::lower($request->input(Fortify::username())).'|'.$request->ip();
}

The Str::transliterate method has been added to core recently and can be used to fix this issue

The throttleKey() method is a package class method, so not something we can fix in our app directly (unless you override all the Fortify calls). I'm also not sure if we can already use that new transliterate method if Fortify supports all of Laravel 8.x and not just the latest release.

Laravel UI package need to bump framework version in composer.json and can start using the transliterate method

Done that here: #219