Workspace Security

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Workspace Phishing
Generic Phishing Methodology
Phishing Methodology
Google Groups Phishing
Apparently by default in workspace members can create groups and invite people to them. You can then modify the email that will be sent to the user adding some links. The email will come from a google address, so it will looks legit and people might click on the link.
Hangout Phishing
You might be able either to directly talk with a person just having his email address or sending an invitation to talk. Either way, modify an email account maybe naming it "Google Security" and adding some Google logos, and the people will think they are talking to google: https://www.youtube.com/watch?v=KTVHLolz6cE&t=904s​
Just the same technique can be used with Google Chat.
Google Doc Phishing
You can create an apparently legitimate document and the in a comment mention some email (like [email protected]). Google will send an email to that email address notifying that he was mentioned in the document. You can put a link in that document to try to make the persona access it.
Google Calendar Phishing
You can create a calendar event and add as many email address of the company you are attacking as you have. Schedule this calendar event in 5 or 15 min from the current time. Make the event looks legit and put a comment indicating that they need to read something (with the phishing link).
To make it looks less suspicious:
Set that the receivers cannot see the other invited people
Do NOT send emails notifying about the event. Then, the people will only see their warning about a meeting in 5mins and that they need to read that link.
Apparently using the API you can set to True that people has accepted the event and even create comments on their behalf.
OAuth Phishing
Any of the previous techniques might be used to make the user access a Google OAuth application that will request the user some access. If the user trust the source he might trust the application (even if it's asking for high privileged permissions).
Note that Google presents an ugly prompt asking warning that the application is untrusted in several cases and from Workspace admins can even prevent people to accept OAuth applications. More on this in the OAuth section.
Password Spraying
In order to test passwords with all the emails you found (or you have generated based in a email name pattern you might have discover) you can use a tool like https://github.com/ustayready/CredKing who will use AWS lambdas to change IP address.
Oauth Apps
Google allows to create applications that can interact on behalf users with several Google services: Gmail, Drive, GCP...
When creating an application to act on behalf other users, the developer needs to create an OAuth app inside GCP and indicate the scopes (permissions) the app needs to access the users data.
When a user wants to use that application, he will be prompted to accept that the application will access to his data specified in the scopes.
This is a very juicy way to phish non-technical users into using applications that access sensitive information because they might not understand the consequences. Therefore, in organizations accounts, there are ways to prevent this from happening.
Unverified App prompt
As it was mentioned, google will always present a prompt to the user to accept the permissions he is giving the application on his behalf. However, if the application is considered dangerous, google will show first a prompt indicating that it's dangerous and making more difficult to the user to grant the permissions to the app.
This prompt appears in apps that:
Uses any scope that can access to private data (Gmail, Drive, GCP, BigQuery...)
Apps with less than 100 users (apps > 100 a review process is needed also to not show the unverified prompt)
Interesting Scopes
You can find here a list of all the Google OAuth scopes.
cloud-platform: View and manage your data across Google Cloud Platform services. You can impersonate the user in GCP.
directory.readonly: See and download your organization's GSuite directory. Get names, phones, calendar URLs of all the users.
App Scripts
Developers can create App Scripts and set them as a standalone project or bound them to Google Docs/Sheets/Slides/Forms. App Scripts is code that will be triggered when a user with editor permission access the doc (and after accepting the OAuth prompt)
However, even if the app isn't verified there are a couple of ways to not show that prompt:
If the publisher of the app is in the same Workspace as the user accessing it
If the script is in a drive of the user
Copy Document Unverified Prompt Bypass
When you create a link to share a document a link similar to this one is created: https://docs.google.com/spreadsheets/d/1i5[...]aIUD/edit
If you change the ending "/edit" for "/copy", instead of accessing it google will ask you if you want to generate a copy of the document.
If someone creates a copy of that document that contained the App Script, he will also be copying the App Script, therefore when he opens the copied spreadsheet, the regular OAuth prompt will appear bypassing the unverified prompt, because the user is now the author of the App Script of the copied file.
This method will be able to bypass also the Workspace admin restriction:
But can be prevented with:
Shared Document Unverified Prompt Bypass
Moreover, if someone shared with you a document with editor access, you can generate App Scripts inside the document and the OWNER (creator) of the document will be the owner of the App Script.
This means, that the creator of the document will appear as creator of any App Script anyone with editor access creates inside of it.
This also means that the App Script will be trusted by the Workspace environment of the creator of the document.
This also means that if an App Script already existed and people has granted access, anyone with Editor permission to the doc can modify it and abuse that access.
To abuse this you also need people to trigger the App Script. And one neat trick if to publish the script as a web app. When the people that already granted access to the App Script access the web page, they will trigger the App Script (this also works using <img> tags.
Post-Exploitation
Google Groups Privesc
By default in workspace a group can be freely accessed by any member of the organization.
Workspace also allow to grant permission to groups (even GCP permissions), so if groups can be joined and they have extra permissions, an attacker may abuse that path to escalate privileges.
You potentially need access to the console to join groups that allow to be joined by anyone in the org. Check groups information in https://groups.google.com/all-groups.
Privesc to GCP Summary
Abusing the google groups privesc you might be able to escalate to a group with some kind of privileged access to GCP
Abusing OAuth applications you might be able to impersonate users and access to GCP on their behalf
Access Groups Mail info
If you managed to compromise a google user session, from https://groups.google.com/all-groups you can see the history of mails sent to the mail groups the user is member of, and you might find credentials or other sensitive data.
Takeout - Download Everything Google Knows about an account
If you have a session inside victims google account you can download everything Google saves about that account from https://takeout.google.com​
Vault - Download all the Workspace data of users
If an organization has Google Vault enabled, you might be able to access https://vault.google.com and download all the information.
Contacts download
From https://contacts.google.com you can download all the contacts of the user.
Cloudsearch
In https://cloudsearch.google.com/ you can just search through all the Workspace content (email, drive, sites...) a user has access to. Ideal to find quickly sensitive information.
Currents
In https://currents.google.com/ you can access a Google Chat, so you might find sensitive information in there.
Google Drive Mining
When sharing a document yo can specify the people that can access it one by one, share it with your entire company (or with some specific groups) by generating a link.
When sharing a document, in the advance setting you can also allow people to search for this file (by default this is disabled). However, it's important to note that once users views a document, it's searchable by them.
For sake of simplicity, most of the people will generate and share a link instead of adding the people that can access the document one by one.
Some proposed ways to find all the documents:
Search in internal chat, forums...
Spider known documents searching for references to other documents. You can do this within an App Script with PaperChaser​
Keep Notes
In https://keep.google.com/ you can access the notes of the user, sensitive information might be saved in here.
Persistence inside a Google account
If you managed to compromise a google user session and the user had 2FA, you can generate an app password and regenerate the 2FA backup codes to know that even if the user change the password you will be able to access his account. Another option instead of regenerating the codes is to enrol your own authenticator app in the 2FA.
Persistence via OAuth Apps
If you have compromised the account of a user, you can just accept to grant all the possible permissions to an OAuth App. The only problem is that Workspace can configure to disallow external and/or internal OAuth apps without being reviewed.
It is pretty common to not trust by default external OAuth apps but trust internal ones, so if you have enough permissions to generate a new OAuth application inside the organization and external apps are disallowed, generate it and use that new internal OAuth app to maintain persistence.
Persistence via delegation
You can just delegate the account to a different account controlled by the attacker.
Persistence via Android App
If you have a session inside victims google account you can browse to the Play Store and install a malware you have already uploaded it directly in the phone to maintain persistence and access the victims phone.
Persistence via Gmail
You can create filters to hide security notifications from Google
from: ([email protected]) "Security Alert"
Hide password reset emails
Create forwarding address to forward sensitive information (or everything) - You need manual access.
Create a forwarding address to send emails that contains the word "password" for example
Add recovery email/phone under attackers control
Persistence via App Scripts
You can create time-based triggers in App Scripts, so if the App Script is accepted by the user, it will be triggered even without the user accessing it.
The docs mention that to use ScriptApp.newTrigger("funcion") you need the scope script.scriptapp, but apparently thats not necessary as long as you have declare some other scope.
Administrate Workspace
In https://admin.google.com/, if you have enough permissions you might be able to modify settings in the Workspace of the whole organization.
You can also search emails through all the users invoices in https://admin.google.com/ac/emaillogsearch​
Account Compromised Recovery
Log out of all sessions
Change user password
Generate new 2FA backup codes
Remove App passwords
Remove OAuth apps
Remove 2FA devices
Remove email forwarders
Remove emails filters
Remove recovery email/phones
Remove bad Android Apps
Remove bad account delegations
References
​https://www.youtube-nocookie.com/embed/6AsVUS79gLw - Matthew Bryant - Hacking G Suite: The Power of Dark Apps Script Magic
​https://www.youtube.com/watch?v=KTVHLolz6cE - Mike Felch and Beau Bullock - OK Google, How do I Red Team GSuite?
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Last modified 18d ago