IMPORTANT: No additional bug fixes or documentation updates will be released for this version. For the latest information, see the current release documentation.
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Elastic Docs ›Elastic Security Solution [8.16] ›Detections and alerts ›Prebuilt rule reference

O365 Exchange Suspicious Mailbox Right Delegation

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O365 Exchange Suspicious Mailbox Right Delegation

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Identifies the assignment of rights to access content from another mailbox. An adversary may use the compromised account to send messages to other accounts in the network of the target organization while creating inbox rules, so messages can evade spam/phishing detection mechanisms.

Rule type: query

Rule indices:

  • filebeat-*
  • logs-o365*

Severity: low

Risk score: 21

Runs every: 5m

Searches indices from: None (Date Math format, see also Additional look-back time)

Maximum alerts per execution: 100

References: None

Tags:

  • Domain: Cloud
  • Data Source: Microsoft 365
  • Use Case: Configuration Audit
  • Tactic: Persistence

Version: 206

Rule authors:

  • Elastic
  • Austin Songer

Rule license: Elastic License v2

Investigation guide

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Setup

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The Office 365 Logs Fleet integration, Filebeat module, or similarly structured data is required to be compatible with this rule.

Rule query

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event.dataset:o365.audit and event.provider:Exchange and event.action:Add-MailboxPermission and
o365.audit.Parameters.AccessRights:(FullAccess or SendAs or SendOnBehalf) and event.outcome:success and
not user.id : "NT AUTHORITY\SYSTEM (Microsoft.Exchange.Servicehost)"

Framework: MITRE ATT&CKTM

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