Microsoft 365 Teams External Access Enabled

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Identifies when external access is enabled in Microsoft Teams. External access lets Teams and Skype for Business users communicate with other users that are outside their organization. An adversary may enable external access or add an allowed domain to exfiltrate data or maintain persistence in an environment.

Rule type: query

Rule indices:

  • filebeat-*
  • logs-o365*

Severity: medium

Risk score: 47

Runs every: 5 minutes

Searches indices from: now-30m (Date Math format, see also Additional look-back time)

Maximum alerts per execution: 100

References:

Tags:

  • Elastic
  • Cloud
  • Microsoft 365
  • Continuous Monitoring
  • SecOps
  • Configuration Audit

Version: 7 (version history)

Added (Elastic Stack release): 7.11.0

Last modified (Elastic Stack release): 8.4.0

Rule authors: Elastic

Rule license: Elastic License v2

Potential false positives

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Teams external access may be enabled by a system or network administrator. Verify that the configuration change was expected. Exceptions can be added to this rule to filter expected behavior.

Investigation guide

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Rule query

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event.dataset:o365.audit and event.provider:(SkypeForBusiness or
MicrosoftTeams) and event.category:web and event.action:"Set-
CsTenantFederationConfiguration" and
o365.audit.Parameters.AllowFederatedUsers:True and
event.outcome:success

Threat mapping

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Framework: MITRE ATT&CKTM

Rule version history

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Version 7 (8.4.0 release)
  • Formatting only
Version 5 (8.1.0 release)
  • Formatting only
Version 4 (7.13.0 release)
  • Formatting only
Version 3 (7.12.0 release)
  • Formatting only
Version 2 (7.11.2 release)
  • Formatting only