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Comment by Ajedi32 | Hacker News Reader

I don't understand your concern. If the attacker controls `https://example.com/.well-known/change-password` wouldn't they also control `https://example.com/my_profile/settings`?

Why bother redirecting the user to a third party site when you can just inject some password-logging JS into the _legitimate_ change password form?

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If an attacker controls a subdomain and can trick a user into visiting it (e.g. evil.example.com), the cookies may be out of scope, but the password manager may (or may not) treat the subdomain as part of the domain in terms of .well-known/change-password requests, allowing a subdomain to redirect the password manager and potentially stealing credentials.

It is undefined behaviour. The spec is under-defined. That's my issue, there has been no security pass of this at all. It is left up to each individual password manager to make this secure (or not).

I assume the password manager is supposed to prepend the host of the login form or whatever host is configured in the password manager.

So if I save example.com in my password manager, it will access example.com/.well-known/change-password no matter which urls I later visit that might be on subdomains of that original page.

If I already configured evil.example.com in my password manager, it's game over anyway before anything relevant to this spec even happens.

I still don't see your point.

If your password manager autofills your credentials for `example.com` when you visit `evil.example.com` then the owner of `evil.example.com` already has an easy way to steal your credentials regardless of whether or not this spec is implemented.

Not necessarily. They can be on two different servers behind a reverse proxy, or the attacker can only write to static files or anything else.

Other attacks would have to be targeted, in most cases. Replacing a standard file under .well-known can be automated.

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