Solutions/Threat Intelligence (NEW)/Analytic Rules/EmailEntity_OfficeActivity.yaml

id: 795d43a3-6edc-4c99-971f-00d05841e5ac
name: TI map Email entity to OfficeActivity
description: |
  'Identifies a match in OfficeActivity table from any Email IOC from TI'
severity: Medium
requiredDataConnectors:
  - connectorId: Office365
    dataTypes:
      - OfficeActivity
  - connectorId: ThreatIntelligence
    dataTypes:
      - ThreatIntelligenceIndicator
  - connectorId: ThreatIntelligenceTaxii
    dataTypes:
      - ThreatIntelligenceIndicator
  - connectorId: MicrosoftDefenderThreatIntelligence
    dataTypes:
      - ThreatIntelligenceIndicator
queryFrequency: 1h
queryPeriod: 14d
triggerOperator: gt
triggerThreshold: 0
tactics:
  - InitialAccess
relevantTechniques:
  - T1566
query: |
  let dt_lookBack = 1h;
  let ioc_lookBack = 14d;
  let emailregex = @'^[a-zA-Z0-9_.+-]+@[a-zA-Z0-9-]+\.[a-zA-Z0-9-.]+$';
  let OfficeEvents = materialize(
    OfficeActivity
    | where isnotempty(UserId)
    | where TimeGenerated >= ago(dt_lookBack)
    | where UserId matches regex emailregex
    | project-rename  OfficeActivity_TimeGenerated = TimeGenerated);
  let OfficeActivityUPNs = OfficeEvents | distinct UserId = tolower(UserId) | summarize make_list(UserId);
  ThreatIntelIndicators
  | extend IndicatorType = replace(@"\[|\]|\""", "", tostring(split(ObservableKey, ":", 0)))
  | where isnotempty(IndicatorType) and IndicatorType == "email-addr"
  | extend EmailSenderAddress = ObservableValue
  | extend EmailSourceDomain = substring(EmailSenderAddress, indexof(EmailSenderAddress, "@") + 1, strlen(EmailSenderAddress) - indexof(EmailSenderAddress, "@") - 1)
  | extend TrafficLightProtocolLevel = tostring(parse_json(AdditionalFields).TLPLevel)
  | where isnotempty(EmailSenderAddress)
  | extend Url = iff(ObservableKey == "url:value", ObservableValue, "")
  | where TimeGenerated >= ago(ioc_lookBack) 
  | where tolower(EmailSenderAddress) in (OfficeActivityUPNs)
  | summarize LatestIndicatorTime = arg_max(TimeGenerated, *) by Id
  | where IsActive == true and ValidUntil > now()
  | extend Description = tostring(parse_json(Data).description)
  | where Description !contains_cs "State: inactive;" and Description !contains_cs "State: falsepos;"
  | project-reorder *, TrafficLightProtocolLevel, EmailSenderAddress, EmailSourceDomain, Type
  // using innerunique to keep perf fast and result set low, we only need one match to indicate potential malicious activity that needs to be investigated
  | join kind=innerunique (OfficeEvents) on $left.EmailSenderAddress == $right.UserId
  | where OfficeActivity_TimeGenerated < ValidUntil
  | summarize OfficeActivity_TimeGenerated = arg_max(OfficeActivity_TimeGenerated, *) by Id, UserId
  | extend Description = tostring(parse_json(Data).description)
  | extend ActivityGroupNames = extract(@"ActivityGroup:(\S+)", 1, tostring(parse_json(Data).labels))
  | project OfficeActivity_TimeGenerated, Description, ActivityGroupNames, Id, ValidUntil, Confidence, EmailSenderAddress, EmailSourceDomain, UserId, ClientIP, Operation, UserType, RecordType, OfficeWorkload, Parameters, Url
  | extend Name = tostring(split(UserId, '@', 0)[0]), UPNSuffix = tostring(split(UserId, '@', 1)[0])
  | extend timestamp = OfficeActivity_TimeGenerated
entityMappings:
  - entityType: Account
    fieldMappings:
      - identifier: FullName
        columnName: UserId
      - identifier: Name
        columnName: Name
      - identifier: UPNSuffix
        columnName: UPNSuffix
  - entityType: IP
    fieldMappings:
      - identifier: Address
        columnName: ClientIP
  - entityType: URL
    fieldMappings:
      - identifier: Url
        columnName: Url
version: 1.2.9
kind: Scheduled