Microsoft 365 Exchange Malware Filter Rule Modification

Elastic Stack Serverless Security

Identifies when a malware filter rule has been deleted or disabled in Microsoft 365. An adversary or insider threat may want to modify a malware filter rule to evade detection.

Rule type: query

Rule indices:

• filebeat-*
• logs-o365*

Severity: medium

Risk score: 47

Runs every: 5m

Searches indices from: now-30m (https://www.elastic.co/guide/en/elasticsearch/reference/current/common-options.html#date-math[Date Math format], see also Additional look-back time)

Maximum alerts per execution: 100

References:

• https://docs.microsoft.com/en-us/powershell/module/exchange/remove-malwarefilterrule?view=exchange-ps
• https://docs.microsoft.com/en-us/powershell/module/exchange/disable-malwarefilterrule?view=exchange-ps

Tags:

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

Version: 7

Rule authors:

• Elastic

Rule license: Elastic License v2

event.dataset:o365.audit and event.provider:Exchange and event.category:web and event.action:("Remove-MalwareFilterRule" or "Disable-MalwareFilterRule") and event.outcome:success

Framework: MITRE ATT&CKTM

• Tactic:

  • Name: Defense Evasion
  • ID: TA0005
  • Reference URL: https://attack.mitre.org/tactics/TA0005/

• Technique:

  • Name: Impair Defenses
  • ID: T1562
  • Reference URL: https://attack.mitre.org/techniques/T1562/