Abnormal successful Microsoft 365 Exchange login event

microsoft-365

Classification:

attack

Tactic:

TA0001-initial-access

Technique:

T1078-valid-accounts

Goal

Detect an Impossible Travel event by a user logging in to Microsoft Exchange.

Strategy

The Impossible Travel detection type’s algorithm compares the GeoIP data of the last and the current Microsoft-365 mailbox login event (@evt.name:MailboxLogin) to determine if the user {{@usr.name}} traveled more than 500km at over 1,000km/hr.

Triage and response

  1. Determine if {{@usr.name}} should be connecting from {{@impossible_travel.triggering_locations.first_location.city}}, {{@impossible_travel.triggering_locations.first_location.country}} and {{@impossible_travel.triggering_locations.second_location.city}}, {{@impossible_travel.triggering_locations.second_location.country}} in a short period of time.
  2. If the user should not be connecting from {{@impossible_travel.triggering_locations.first_location.city}}, {{@impossible_travel.triggering_locations.first_location.country}} and {{@impossible_travel.triggering_locations.second_location.city}}, {{@impossible_travel.triggering_locations.second_location.country}}, then consider isolating the account and reset credentials.
  3. Use the Cloud SIEM - User Investigation dashboard to audit any user actions that may have occurred after the illegitimate login.