M365TEAMS-006: Messaging policies (external communication)
- Platform
- Entra ID / M365
- Category
- Microsoft Teams Security
- Severity
- Medium
- Zero Trust pillar
- Applications & Workloads (weight 1)
- Golden fixtures
- 3
- Branch coverage
- Observed: fixtures prove the verdicts they exercise
- Provenance
- baseline
What it checks
Teams messaging policies control user capabilities within chat and channel conversations, including the ability to communicate with external users through chat. Unrestricted messaging to external users enables data exfiltration through chat, file sharing, and link sharing without the visibility and controls applied to email communication. Messaging policies must be configured to prevent sensitive data leakage through the Teams chat channel.
Recommended value
External chat limited to specific domains; URL preview disabled for external conversations; file sharing restricted in external chats
Remediation
Review the Teams messaging policies and restrict the ability to chat with external users to only those personnel who have a business need for cross-organization communication. Disable URL previews in conversations with external users to prevent accidental data exposure through link expansion. Consider implementing DLP policies for Teams chat to detect and block sharing of sensitive information types in external conversations.
Fixture-proven verdicts
Every verdict below is proven by a golden fixture in the module's gating test suite. This table derives from the last green run; it cannot be edited by hand.
| Scenario | Expected verdict |
|---|---|
| clean | PASS |
| known-bad | WARN |
| no-data | Not Assessed |
Framework mappings
- CISA SCuBA
- MS.TEAMS.2.2v2, MS.TEAMS.2.3v2
- NIST SP 800-53
- AC-20
- CIS M365 Benchmark
- 8.2.1