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m365

Meeting chat for untrusted organizations is disabled

teams_meeting_external_chat_disabled
Service: teamsSeverity: high
OfficialBuilt-inVerified
Categories:trust-boundariese3
Resource Type:NotDefined

Microsoft 365 Teams meeting policy setting AllowExternalNonTrustedMeetingChat governs whether users can read or send chat messages in meetings hosted by untrusted organizations.

This assesses the org-wide default policy to confirm external meeting chat with non-trusted tenants is blocked.

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Risk

Permitting chat in external meetings with untrusted tenants risks:

  • Confidential data exposure via messages/files
  • Malware delivery through links or media (e.g., GIF-based techniques)
  • Social engineering enabling account compromise and lateral movement, degrading confidentiality and integrity

Run this check with Prowler

Run in Prowler Cloud
Run
prowler m365 --checks teams_meeting_external_chat_disabled

Recommendation

Block chat for meetings hosted by non-trusted organizations and restrict collaboration to a vetted allowlist.

Adopt defense in depth: limit content sharing, enable link/file scanning, enforce DLP, and user training. Review external trust relationships regularly per least privilege.

Remediation

CLI

Set-CsTeamsMeetingPolicy -Identity Global -AllowExternalNonTrustedMeetingChat $False

Other

1Sign in to the Teams admin center: https://admin.teams.microsoft.com
2Go to Meetings > Meeting policies
3Select Global (Org-wide default)
4Under Meeting engagement, set External meeting chat (untrusted organizations) to Off
5Click Save

Check Code

from typing import List

from prowler.lib.check.models import Check, CheckReportM365
from prowler.providers.m365.services.teams.teams_client import teams_client


class teams_meeting_external_chat_disabled(Check):
    """Check if external meeting chat is disabled.

    Attributes:
        metadata: Metadata associated with the check (inherited from Check).
    """

    def execute(self) -> List[CheckReportM365]:
        """Execute the check for external meeting chat settings.

        This method checks if external meeting chat is disabled for untrusted organizations.

        Returns:
            List[CheckReportM365]: A list of reports containing the result of the check.
        """
        findings = []
        global_meeting_policy = teams_client.global_meeting_policy
        if global_meeting_policy:
            report = CheckReportM365(
                metadata=self.metadata(),
                resource=global_meeting_policy if global_meeting_policy else {},
                resource_name="Teams Meetings Global (Org-wide default) Policy",
                resource_id="teamsMeetingsGlobalPolicy",
            )
            report.status = "FAIL"
            report.status_extended = (
                "External meeting chat is enabled for untrusted organizations."
            )

            if not global_meeting_policy.allow_external_non_trusted_meeting_chat:
                report.status = "PASS"
                report.status_extended = (
                    "External meeting chat is disabled for untrusted organizations."
                )

            findings.append(report)

        return findings

References