Email Domain Permissions: Security Risks

TL;DR

Automatically giving people access to systems based *only* on their work email domain is risky. It’s easy for attackers to abuse, and it can lead to data breaches. Use stronger methods like multi-factor authentication (MFA) and individual user accounts.

Why Relying on Email Domains is a Bad Idea

Many organisations try to simplify access management by trusting email domains. For example, anyone with an @example.com address gets certain permissions. While convenient, this approach has serious security flaws:

• Domain Spoofing: Attackers can often *fake* emails from legitimate domains.
• Compromised Accounts: If someone’s email account is hacked, the attacker automatically gets all associated permissions.
• Leaver Issues: When someone leaves a company, their access isn’t immediately revoked just because they no longer have that email address.
• Partner/Vendor Access: Giving broad access to partner domains can be too permissive.

How Attackers Exploit Email Domain Trust

An attacker could:

• Register a domain similar to yours (e.g., examp1e.com instead of example.com).
• Compromise an email account at a trusted partner organisation.
• Use a legitimate-looking email address to gain access to your systems.

A Step-by-Step Guide to Better Security

1. Stop Automatic Permissions: Immediately disable any rules that grant access solely based on email domain. This is the most important step.
2. Implement Individual User Accounts: Every user needs their *own* account with a unique username and password.
3. Enable Multi-Factor Authentication (MFA): MFA adds an extra layer of security, even if someone steals a password. Consider using authenticator apps or hardware tokens.

   # Example: Enabling MFA for a user in Google Workspace

   gcloud iam service-accounts add-iam-policy-binding YOUR_PROJECT_ID --member 'user:user@example.com' --role 'roles/iam.securityAdmin'

4. Least Privilege Principle: Grant users only the *minimum* permissions they need to do their job. Don’t give everyone admin access!
5. Regular Access Reviews: Periodically check who has access to what, and revoke unnecessary permissions.
   • Automate this process where possible using scripts or identity management tools.
   • Document the reasons for each permission granted.
6. Strong Password Policies: Enforce strong, unique passwords and regular password changes.
7. Monitor Login Activity: Look for suspicious login attempts (e.g., from unusual locations or at odd hours). Use a Security Information and Event Management (SIEM) system if possible.

   # Example: Checking recent logins in Linux using 'last' command

   last -n 20 user@example.com

8. Email Authentication Protocols: Implement SPF, DKIM and DMARC to help prevent email spoofing.
   • SPF (Sender Policy Framework) specifies which mail servers are allowed to send emails on behalf of your domain.
   • DKIM (DomainKeys Identified Mail) adds a digital signature to emails.
   • DMARC (Domain-based Message Authentication, Reporting & Conformance) tells email receivers what to do with emails that fail SPF or DKIM checks.

Tools That Can Help

• Identity and Access Management (IAM) Systems: Okta, Azure Active Directory, Google Cloud IAM.
• Security Information and Event Management (SIEM) Systems: Splunk, Sumo Logic, ELK Stack.
• Password Managers: 1Password, LastPass.