Microsoft Teams: Multi-line Calling on Teams Mobile

🚨 The Signal: Teams mobile now supports multiple phone lines, allowing users to select a line for calls. This increases the attack surface for mobile devices and requires re-evaluation of mobile calling policies and identity management.

The Impact

Mobile users are affected, increasing the risk of identity confusion and potential data leakage through unmanaged lines.

• Mobile users: Increased risk of misattributing calls to personal vs. business lines.
• Security teams: New vectors for data exfiltration via unmonitored lines.
• Compliance teams: Challenges in logging and auditing communications from multiple lines.
• Identity teams: Complexity in managing and attributing multiple phone identities to a single user.

The Action

1. Review existing Microsoft Teams calling policies for mobile devices.
2. Assess the necessity of multi-line calling for specific user groups.
3. Implement or update Conditional Access policies for Teams mobile to enforce device compliance.
4. Educate users on appropriate use of multi-line calling and data handling.
5. Monitor Teams call logs for unusual activity related to multi-line usage.

Domain: Teams · Impact: medium · Workload: Teams