Comment by nodamage
2 days ago
> In the case of Google OAuth, it's possible to forego this in order to allow any Google user from any Google workspace to login to your application.
There are plenty of use cases where this is appropriate. If you wanted to allow users to login to Hacker News with their Google accounts you would use this option because you do not care what workspace they belong to.
> Some applications (e.g. Tailscale) take advantage of the public Google OAuth API to provide private internal corporate accounts.
This is a misuse of the public Google OAuth API. Your first link clearly states: "A public application allows access to users outside of your organization (@your-organization.com). Access can be from consumer accounts, like @gmail.com, or other organizations, like @partner-organization.com." In other words it is intended for scenarios where you want to allow access to users outside your workspace.
> Instead, Google instructs you to look at the "hd" parameter, specific to Google, to determine the Google Workspace a given user belongs to for security purposes.
According to your second link the "hd" parameter only tells you what domain the user belongs to, it does not tell you what workspace the user belongs to.
> You can avoid this issue by using a custom Google OIDC IdP configured for internal access only in your applications, rather than using a pre-configured public Google OIDC IdP
So Google offers an OAuth integration option that actually restricts access to your specific workspace. Choosing to ignore this option and instead integrating with the option designed for public access from all Google accounts, and then calling it a vulnerability when someone can login with an account from another workspace, is frankly, absurd.
> This is a misuse of the public Google OAuth API. Your first link clearly states: "A public application allows access to users outside of your organization (@your-organization.com). Access can be from consumer accounts, like @gmail.com, or other organizations, like @partner-organization.com." In other words it is intended for scenarios where you want to allow access to users outside your workspace.
> According to your second link the "hd" parameter only tells you what domain the user belongs to, it does not tell you what workspace the user belongs to.
From the docs:
> If you need to validate that the ID token represents a Google Workspace or Cloud organization account, you can check the `hd` claim, which indicates the hosted domain of the user. This must be used when restricting access to a resource to only members of certain domains. The absence of this claim indicates that the account does not belong to a Google hosted domain.
https://developers.google.com/identity/gsi/web/guides/verify...
Note also that even Google conflates "domains" with "Google hosted domains" with "Google Workspace or Cloud organization accounts."
> Choosing to ignore this option and instead integrating with the option designed for public access from all Google accounts, and then calling it a vulnerability when someone can login with an account from another workspace, is frankly, absurd.
At this point, if you still believe calling this a vulnerability is absurd, I don't think there's anything more I can say to convince you. Google paid out the bounty because they didn't believe it was abusrd.
I personally think that the best counterargument to calling it a vulnerability is: "well, sure, Google is reusing the Google Workspace identifier for different workspaces, which could be used to impersonate a user; but if you own the domain, you can also receive email as that user and reset the account that way."
I suppose this comes down to the interpretation of the documentation. Note that it only says "a workspace", not "a specific workspace" or "which workspace".
1) The "hd" claim tells you that the user is a member of a workspace. If the user is a member of a workspace it tells you the domain name of that workspace.
2) The "hd" claim tells you which specific workspace the user is a member of.
You are taking interpretation (2) whereas I am taking interpretation (1). I believe interpretation (1) is correct given the next sentence says you can use the "hd" claim to restrict access to only members of certain domains. If interpretation (2) was intended, they could have instead said you can use the "hd" claim to restrict access to only members of a certain workspace.
If Google is at fault for anything here it is for writing confusing documentation, however given the totality of the documentation where:
a) Google describes public applications as intended for logins from all Google accounts regardless of workspace, and
b) Google offers the internal application option for situations where you want to restrict logins to users of a specific workplace,
I'm going to stand by my conclusion that the real fault lies with service providers choosing the wrong integration option in the first place and then making invalid assumptions about what information the "hd" claim supplies in the public option.