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Comment by Someone1234 | Hacker News Reader

Seems like a nice subtle way to hijack the changing password mechanism, particularly on a sub-domain you control. Just set the URL to e.g. "https://evilsite/changepasswords" and wait for Password Managers to be updated.

The fact that the spec says nothing about where a user can be redirected, and which domains/sub-domains are within scope for which change password requests seems like an oversight.

For example if my password manager saves a password for login.example.com, is a .well-known/Change-Password on evil.example.com, or example.com in scope? Who decides? Is it left to the password manager to figure out the security scope?

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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?

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.

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.

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

Well, since password managers already tie a password to a specific domain, presumably they would use the same logic for determining the scope of the well-known URL. I do agree that the spec could probably benefit from clarifying this, but I bet "the same domain as one of the recorded login URLs" is sufficient. (And the password manager would never even know to check evil.example.com if you hadn't ever put that password into that subdomain).

> but I bet "the same domain as one of the recorded login URLs" is sufficient.

What is that a quote from? I cannot find it in the spec here:

https://wicg.github.io/change-password-url/index.html

Sorry, intended as a hypothetical suggestion, not a quote.

Oh understood. Yeah that suggestion would fix my concerns almost wholesale. They just need to think about scoping it to e.g. domain, subdomain, etc.

Changing your password for a google account seems to involve going to myaccount.google.com (which is not the domain your login is associated with) - so clearly this needs to support redirects to different subdomains.

This is being tracked by https://github.com/WICG/change-password-url/issues/8

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