The Sharing Perimeter Vulnerability
One of the greatest strengths of Google Workspace is its frictionless collaboration. A marketing employee can create a massive Google Sheet containing a list of 5,000 corporate clients, click the blue “Share” button, type in an external vendor’s @gmail.com address, and instantly grant them full editing access to the proprietary data.
This frictionless design is also a massive security nightmare. If a disgruntled employee is preparing to leave for a competitor, they can quietly share dozens of highly classified Google Drive folders with their own personal Gmail account, effectively exfiltrating gigabytes of corporate data without triggering standard email monitoring systems.
Historically, administrators had to choose a binary option in the Google Admin Console: either allow external sharing for everyone or block it entirely (which breaks legitimate business workflows). To solve this, Google introduced Trust Rules. Trust Rules provide a granular, hyper-specific policy engine that allows administrators to dictate exactly who can share what with whom, based on Organizational Units (OUs), specific domain names, and file ownership.
Step 1: Enabling the Trust Rules Engine
Trust Rules completely replace the legacy Google Drive sharing settings. Before you can build rules, you must transition your domain to the new engine.
- Log into the Google Workspace Admin Console (admin.google.com).
- Navigate to Rules (located on the main dashboard, or under Security > Access and data control > Trust rules).
- If you have never used this feature, you will see a prompt to “Turn on trust rules.” Click it to initiate the migration. Google will automatically convert your existing legacy sharing settings into equivalent baseline Trust Rules.
Step 2: Understanding the Trust Rule Architecture
A Trust Rule is fundamentally an IF/THEN logic statement applied to a specific group of users.
For example: IF the Finance Team attempts to share a file, THEN they are only permitted to share it with @ourcompany.com and @our-auditors.com.
When creating a rule, you must define three parameters:
- Scope: Which internal users does this rule apply to? (e.g., The “Finance” Organizational Unit).
- Action: What are these users trying to do? (e.g., Sharing a file they own, or Receiving a file owned by someone else).
- Conditions: Who are they allowed to interact with? (e.g., Trusted Domains, specific external OUs, or anyone on the internet).
Step 3: Creating a Strict Internal-Only Rule
Suppose you want to lock down your Engineering department. Engineers handle source code and proprietary algorithms. They should never be allowed to share Google Drive files with anyone outside the company, under any circumstances.
- In the Trust Rules dashboard, click Create rule.
- Name it “Engineering Strict Lockdown”.
- Scope: Select the Organizational Unit containing your Engineers (e.g.,
/Employees/Engineering). - Action: Check the box for Sharing files owned by users in the selected scope.
- Conditions: Select Internal users only. Do not check any other boxes.
- Save and activate the rule.
The next time an engineer opens a Google Doc and tries to share it with [email protected], Google Drive will instantly intercept the action and throw a red error message stating that corporate policy blocks the action.
Step 4: Whitelisting Trusted Vendor Domains
The Marketing department, unlike Engineering, must collaborate with external PR agencies. If you apply the “Internal Only” rule to Marketing, they will be unable to work.
Instead, you must create a whitelist rule for Marketing, allowing them to share files only with specific, vetted corporate partners.
- First, navigate to Directory > Organizational settings > Trusted domains. You must explicitly add the PR agency’s domain (e.g.,
pr-agency.com) to your corporate whitelist. - Go back to the Trust Rules dashboard and click Create rule.
- Scope: Select the Marketing OU (
/Employees/Marketing). - Action: Select Sharing files owned by users in the selected scope.
- Conditions: Check Internal users AND check Trusted domains.
Now, if a Marketing employee tries to share a file with [email protected], the action succeeds. If they try to share the exact same file with random-competitor.com or a standard @gmail.com address, the action is blocked.
Step 5: Controlling Inbound Data (Receiving Files)
Data exfiltration is only half the threat model. The other half is inbound malware and phishing.
If an attacker creates a malicious Google Doc containing phishing links and shares it with your CEO’s corporate email, it will appear in the CEO’s “Shared with me” folder, completely bypassing Gmail’s spam filters.
Trust Rules can govern receiving files as well.
Create a new rule targeting the entire company (the root OU). Change the Action to Receiving files from users outside the selected scope. Set the condition to only allow receiving from Trusted Domains. This guarantees that random internet users cannot inject malicious Google Drive files into your employees’ corporate workspaces.
Conclusion
Treating Google Drive sharing as a binary “on/off” switch forces organizations to compromise between productivity and security. By transitioning to Google Workspace Drive Trust Rules, IT administrators can construct surgical, department-level data perimeters. You can enforce absolute lockdown on engineering intellectual property while simultaneously allowing the sales team to seamlessly collaborate with vetted external partners, ensuring data security without breaking business workflows.