NRT Multiple users email forwarded to same destination

id: 3b05727d-a8d1-477d-bbdd-d957da96ac7b
name: NRT Multiple users email forwarded to same destination
description: |
  'Identifies when multiple (more than one) users mailboxes are configured to forward to the same destination.
  This could be an attacker-controlled destination mailbox configured to collect mail from multiple compromised user accounts.'
severity: Medium
requiredDataConnectors:
  - connectorId: Office365
    dataTypes:
      - OfficeActivity
tactics:
  - Collection
  - Exfiltration
relevantTechniques:
  - T1114
  - T1020
query: |
  OfficeActivity
  | where OfficeWorkload =~ "Exchange"
  | where Parameters has_any ("ForwardTo", "RedirectTo", "ForwardingSmtpAddress")
  | mv-apply DynamicParameters = todynamic(Parameters) on (summarize ParsedParameters = make_bag(pack(tostring(DynamicParameters.Name), DynamicParameters.Value)))
  | evaluate bag_unpack(ParsedParameters, columnsConflict='replace_source')
  | extend DestinationMailAddress = tolower(case(
      isnotempty(column_ifexists("ForwardTo", "")), column_ifexists("ForwardTo", ""),
      isnotempty(column_ifexists("RedirectTo", "")), column_ifexists("RedirectTo", ""),
      isnotempty(column_ifexists("ForwardingSmtpAddress", "")), trim_start(@"smtp:", column_ifexists("ForwardingSmtpAddress", "")),
      ""))
  | where isnotempty(DestinationMailAddress)
  | mv-expand split(DestinationMailAddress, ";")
  | extend ClientIPValues = extract_all(@'\[?(::ffff:)?(?P<IPAddress>(\d+\.\d+\.\d+\.\d+)|[^\]]+)\]?([-:](?P<Port>\d+))?', dynamic(["IPAddress", "Port"]), ClientIP)[0]
  | extend ClientIP = tostring(ClientIPValues[0]), Port = tostring(ClientIPValues[1])
  | summarize StartTime = min(TimeGenerated), EndTime = max(TimeGenerated), DistinctUserCount = dcount(UserId), UserId = make_set(UserId, 250), Ports = make_set(Port, 250), EventCount = count() by tostring(DestinationMailAddress), ClientIP
  | where DistinctUserCount > 1
  | mv-expand UserId to typeof(string)
entityMappings:
  - entityType: Account
    fieldMappings:
      - identifier: FullName
        columnName: UserId
  - entityType: IP
    fieldMappings:
      - identifier: Address
        columnName: ClientIP
version: 1.0.3
kind: NRT
metadata:
    source:
        kind: Community
    author:
        name: Pete Bryan
    support:
        tier: Community
    categories:
        domains: [ "Security - Threat Protection" ]