4 ms·

>Then, the impostors in step #3 create a different google account with the same domain, and Google says "yeah, these are definitely the same guys as before", ev

>Then, the impostors in step #3 create a different google account with the same domain, and Google says "yeah, these are definitely the same guys as before", even though Google is fully capable of discerning that that is not the case; these are different people with a different workspace account, different names, different payment information, and so on, but Google is saying that if you're holding the domain you are therefore the same people as far as they're concerned and is asserting that to other companies. Yep I understand the mechanism by which this gets abused; I think we just disagree on the implications. I don't work for Google but it seems from the outside that they're treating the OIDC subject claim as referencing the domain attached to the workspace account, or something similar. I've seen implementations where the `sub` claim is more granular, so to me that indicates the field is underspecified. Given all that, I suppose TFAuthor's proposed solution is a good way forward. I still think classifying this as an OAuth vulnerability isn't correct.

radlad 2y ago
Traditionally, SAML / OIDC trust is established using public/private keypairs. Each IdP/SP pair gets a unique combination. In this case, a domain changing hands would not allow the new owner to gain access to the old owner's accounts. 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. See the distinction between "public and internal applications" here: https://support.google.com/cloud/answer/6158849?hl=en#zippy=%2Cpublic-and-internal-applications https://support.google.com/cloud/answer/6158849?hl=en#zippy=... Some applications (e.g. Tailscale) take advantage of the public Google OAuth API to provide private internal corporate accounts. A common misconfiguration here is to use the domain portion of the "email" attribute - this can be spoofed by Google Workspace admins. That's not what's happening here. 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. This field cannot be overridden by Google Workspace admins. The trust breaks down when the domain changes hands, a new Google Workspace account is opened, but the old "hd" value is reused. You can read more about "hd" here: https://developers.google.com/identity/openid-connect/openid-connect https://developers.google.com/identity/openid-connect/openid... (find the table and read the descriptions for both "email" and "hd".) 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 (be very careful you mark it internal!) A new domain owner would not be able to retrieve the secret key you previously generated.
- anon84873628 2y ago
  To clarify, any multi-tenant app that has a Google login button that "just works" without you having to set up your own OAuth client creds is using the "public" app option. Effectively the OAuth client side doesn't care whether you use a public Gmail account or enterprise Workspaces account to login. However, on the Workspace Admin side you can set policies as to whether the org accounts can login to arbitrary public apps by default, or set up an app allowlist, etc. It's definitely a best practice not to let your users login to arbitrary apps, even if it's only for the profile data and not other API scopes. If you do login to a public app with an org account, how that app decides to group/authorize users from (what it perceived as) the same org/domain could be a sensitive procedure with opportunity for exploit, and it seems like maybe Google should offer a more reliable unique org id claim. If you are making your own internal app then client is going to be internal only by default. Note this is managed in a GCP project. If you're using Workspace and GCP then you may want to use GCP services with built-in Google auth like Cloud Functions, App Engine, Identity Aware Proxy, etc.
- deleted 2y ago
  [deleted]
- delfinom 2y ago
  Yea "hd" doesn't work here. Users can make google accounts with corporate domains but without gsuite hosting attached. The same concern applies to just @gmail.com addys. Google has gotten big on nuking inactive accounts now, what stops similar openings where a person's inactive account gets recreated by an attacker and waltz his way into SSO systems? There's some corporate systems (usually benefits) that allow personal emails attached to the same account as work emails for example. I imagine the fact the author is writing that Google reopened the bug and is issuing a bounty means there are Google engineers more than aware of the issue rather than trying to argue what Google does and does not intend.
  - the-rc 2y ago
    Once a Gmail account is deleted, it can't be recreated by anyone, including the original owner.

radlad 2y ago

Traditionally, SAML / OIDC trust is established using public/private keypairs. Each IdP/SP pair gets a unique combination. In this case, a domain changing hands would not allow the new owner to gain access to the old owner's accounts. 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. See the distinction between "public and internal applications" here: https://support.google.com/cloud/answer/6158849?hl=en#zippy=%2Cpublic-and-internal-applications https://support.google.com/cloud/answer/6158849?hl=en#zippy=... Some applications (e.g. Tailscale) take advantage of the public Google OAuth API to provide private internal corporate accounts. A common misconfiguration here is to use the domain portion of the "email" attribute - this can be spoofed by Google Workspace admins. That's not what's happening here. 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. This field cannot be overridden by Google Workspace admins. The trust breaks down when the domain changes hands, a new Google Workspace account is opened, but the old "hd" value is reused. You can read more about "hd" here: https://developers.google.com/identity/openid-connect/openid-connect https://developers.google.com/identity/openid-connect/openid... (find the table and read the descriptions for both "email" and "hd".) 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 (be very careful you mark it internal!) A new domain owner would not be able to retrieve the secret key you previously generated.

anon84873628 2y ago
To clarify, any multi-tenant app that has a Google login button that "just works" without you having to set up your own OAuth client creds is using the "public" app option. Effectively the OAuth client side doesn't care whether you use a public Gmail account or enterprise Workspaces account to login. However, on the Workspace Admin side you can set policies as to whether the org accounts can login to arbitrary public apps by default, or set up an app allowlist, etc. It's definitely a best practice not to let your users login to arbitrary apps, even if it's only for the profile data and not other API scopes. If you do login to a public app with an org account, how that app decides to group/authorize users from (what it perceived as) the same org/domain could be a sensitive procedure with opportunity for exploit, and it seems like maybe Google should offer a more reliable unique org id claim. If you are making your own internal app then client is going to be internal only by default. Note this is managed in a GCP project. If you're using Workspace and GCP then you may want to use GCP services with built-in Google auth like Cloud Functions, App Engine, Identity Aware Proxy, etc.
deleted 2y ago
[deleted]
delfinom 2y ago
Yea "hd" doesn't work here. Users can make google accounts with corporate domains but without gsuite hosting attached. The same concern applies to just @gmail.com addys. Google has gotten big on nuking inactive accounts now, what stops similar openings where a person's inactive account gets recreated by an attacker and waltz his way into SSO systems? There's some corporate systems (usually benefits) that allow personal emails attached to the same account as work emails for example. I imagine the fact the author is writing that Google reopened the bug and is issuing a bounty means there are Google engineers more than aware of the issue rather than trying to argue what Google does and does not intend.
- the-rc 2y ago
  Once a Gmail account is deleted, it can't be recreated by anyone, including the original owner.