Classification:

attack

Tactic:

TA0005-defense-evasion

Technique:

T1564-hide-artifacts

VIEW RULE IN DATADOG VIEW SIGNALS

Goal

Detect when a user configures an inbox rule with a name commonly associated with business email compromises.

Strategy

Monitor Microsoft 365 Exchange audit logs to look for the operation New-InboxRule or Set-InboxRule. Attackers might set up email rules to hide incoming emails in a compromised user mailbox to hide their activities or maintain access to the victim’s inbox. Attackers may use simple names like . or ... for their malicious inbox rules, which are uncommon in most environments.

Triage and response

1. Inspect the inbox rule for any indicators:
   • Suspicious keywords in the filter.
   • The rule name.
2. Determine if there is a legitimate use case for the inbox rule by contacting the user {{@usr.email}}.
3. If {{@usr.email}} is not aware of the inbox rule:
   • Investigate other activities performed by the user {{@usr.email}} using the Cloud SIEM - User Investigation dashboard.
   • Begin your organization’s incident response process and investigate.

Changelog

• 1 July 2024 - Updated rule query.
• 23 July 2024 - Updated rule query.