Hackers Create Hidden Mailbox Rules in Microsoft 365 to Intercept Sensitive Business Emails

The article highlights a sophisticated tactic used by hackers to exploit hidden mailbox rules within Microsoft 365, enabling them to intercept and manipulate sensitive business emails. Here are the key points:

1. Methodology: Hackers create hidden mailbox rules that automatically forward incoming emails to external accounts or filter out specific types of messages (e.g., password reset requests) without alerting the user.

2. Persistence Mechanism: These rules allow attackers to maintain long-term access to compromised accounts, facilitating persistent data exfiltration and manipulation.

3. Detection Challenges:

   • Hidden rules are difficult to detect through standard monitoring tools.
   • They can bypass email filtering mechanisms designed to prevent unauthorized external communications.

4. Impact: This technique has been used in real-world attacks targeting financial institutions, potentially leading to significant financial losses and reputational damage.

5. Mitigation Strategies:

   • Disable automatic external forwarding in Exchange Online.
   • Enforce multi-factor authentication (MFA) with conditional access policies.
   • Regularly audit mailbox rules for suspicious activities.
   • Monitor OAuth consent grants for unusual application permissions.
   • Review Entra ID sign-in logs for risky authentication events.

6. Recommendations: Organizations should implement

Read the full article at Cyber Security News

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