O365 Exchange Suspicious Mailbox Right Delegation
editO365 Exchange Suspicious Mailbox Right Delegation
editIdentifies 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: 5 minutes
Searches indices from: now-6m (Date Math format, see also Additional look-back time)
Maximum alerts per execution: 100
Tags:
- Elastic
- Cloud
- Microsoft 365
- Continuous Monitoring
- SecOps
- Configuration Audit
Version: 2 (version history)
Added (Elastic Stack release): 7.16.0
Last modified (Elastic Stack release): 8.1.0
Rule authors: Elastic, Austin Songer
Rule license: Elastic License v2
Potential false positives
editAssignment of rights to a service account.
Investigation guide
edit## Config The Office 365 Logs Fleet integration, Filebeat module, or similarly structured data is required to be compatible with this rule.
Rule query
editevent.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)"
Threat mapping
editFramework: MITRE ATT&CKTM
-
Tactic:
- Name: Persistence
- ID: TA0003
- Reference URL: https://attack.mitre.org/tactics/TA0003/
-
Technique:
- Name: Account Manipulation
- ID: T1098
- Reference URL: https://attack.mitre.org/techniques/T1098/
Rule version history
edit- Version 2 (8.1.0 release)
-
-
Updated query, changed from:
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
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