TI map Domain entity to EmailEvents

Severity: medium
Time window: 14d
Group by: IndicatorId, RecipientEmailAddress, RecipientEmailDomain, SenderFromDomain, TI_Domain
Source: github.com/Azure/Azure-Sentinel

Identifies a match in EmailEvents table from any Domain IOC from TI

MITRE ATT&CK coverage

Tactic	Techniques
Initial Access	`T1566` Phishing

Telemetry coverage

Platform	Record / event type
Microsoft Defender for Endpoint	`EmailEvents` action `any`: Email processed

Rule body

id: 96307710-8bb9-4b45-8363-a90c72ebf86f
name: TI map Domain entity to EmailEvents
description: |
  Identifies a match in EmailEvents table from any Domain IOC from TI
severity: Medium
requiredDataConnectors:
  - connectorId: Office365
    dataTypes:
      - EmailEvents
  - 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 EmailEvents_ = materialize(EmailEvents | where isnotempty(RecipientEmailAddress) and isnotempty(SenderFromAddress) and TimeGenerated >= ago(dt_lookBack) and DeliveryAction !has "Blocked" | project-rename  EmailEvents_TimeGenerated = TimeGenerated | extend SenderFromDomain = tolower(SenderFromDomain) | extend RecipientEmailDomain = tolower(tostring(split(RecipientEmailAddress, '@', 1))));
  let SenderDomains = EmailEvents_ | distinct  SenderFromDomain | summarize make_list(SenderFromDomain);
  let RecipientDomains = EmailEvents_ | distinct  RecipientEmailDomain | summarize make_list(RecipientEmailDomain);
  let TI = materialize(ThreatIntelligenceIndicator
  | where TimeGenerated >= ago(ioc_lookBack)
  | where isnotempty(DomainName)
  | extend TI_Domain = tolower(DomainName)
  | where TI_Domain in (SenderDomains) or TI_Domain in (RecipientDomains)
  | summarize LatestIndicatorTime = arg_max(TimeGenerated, *) by IndicatorId
  | where Active == true and ExpirationDateTime > now()
  | where Description !contains_cs "State: inactive;" and Description !contains_cs "State: falsepos;");
  (union
    (TI | join kind=innerunique (EmailEvents_) on $left.TI_Domain == $right.SenderFromDomain),
    (TI | join kind=innerunique (EmailEvents_) on $left.TI_Domain == $right.RecipientEmailDomain))
  | where EmailEvents_TimeGenerated < ExpirationDateTime
  | summarize EmailEvents_TimeGenerated = arg_max(EmailEvents_TimeGenerated, *) by IndicatorId, RecipientEmailAddress
  | project EmailEvents_TimeGenerated, Description, ActivityGroupNames, IndicatorId, ThreatType, ExpirationDateTime, ConfidenceScore, DomainName, RecipientEmailAddress, SenderFromAddress, Subject, ConfidenceLevel, Url, Type, TI_Domain, TrafficLightProtocolLevel, DeliveryAction, DeliveryLocation, EmailDirection
  | extend Name = tostring(split(RecipientEmailAddress, '@', 0)[0]), UPNSuffix = tostring(split(RecipientEmailAddress, '@', 1)[0])
  | extend timestamp = EmailEvents_TimeGenerated
entityMappings:
  - entityType: Account
    fieldMappings:
      - identifier: FullName
        columnName: RecipientEmailAddress
      - identifier: Name
        columnName: Name
      - identifier: UPNSuffix
        columnName: UPNSuffix
version: 1.0.2
kind: Scheduled

Stages and Predicates

Parameters

let dt_lookBack = 1h;
let ioc_lookBack = 14d;

Let binding: `EmailEvents_`

let EmailEvents_ = materialize(EmailEvents | where isnotempty(RecipientEmailAddress) and isnotempty(SenderFromAddress) and TimeGenerated >= ago(dt_lookBack) and DeliveryAction !has "Blocked" | project-rename  EmailEvents_TimeGenerated = TimeGenerated | extend SenderFromDomain = tolower(SenderFromDomain) | extend RecipientEmailDomain = tolower(tostring(split(RecipientEmailAddress, '@', 1))));

Let binding: `SenderDomains`

let SenderDomains = EmailEvents_ | distinct  SenderFromDomain | summarize make_list(SenderFromDomain);

Let binding: `RecipientDomains`

let RecipientDomains = EmailEvents_ | distinct  RecipientEmailDomain | summarize make_list(RecipientEmailDomain);

union (2 sources)

Each leg below queries one source; the rule matches if any leg does. Sources: TI, TI

Leg 1: `TI`

TI | join kind=innerunique (EmailEvents_) on $left.TI_Domain == $right.SenderFromDomain

Leg 2: `TI`

TI | join kind=innerunique (EmailEvents_) on $left.TI_Domain == $right.RecipientEmailDomain

Applied to the combined result

| where EmailEvents_TimeGenerated < ExpirationDateTime
| summarize EmailEvents_TimeGenerated = arg_max(EmailEvents_TimeGenerated, *) by IndicatorId, RecipientEmailAddress
| project EmailEvents_TimeGenerated, Description, ActivityGroupNames, IndicatorId, ThreatType, ExpirationDateTime, ConfidenceScore, DomainName, RecipientEmailAddress, SenderFromAddress, Subject, ConfidenceLevel, Url, Type, TI_Domain, TrafficLightProtocolLevel, DeliveryAction, DeliveryLocation, EmailDirection
| extend Name = tostring(split(RecipientEmailAddress, '@', 0)[0]), UPNSuffix = tostring(split(RecipientEmailAddress, '@', 1)[0])
| extend timestamp = EmailEvents_TimeGenerated

Exclusions

The rule actively suppresses these predicates.

Field	Kind	Excluded values	Search
`Description`	contains	`State: falsepos;`	`excludes:Description` `field:"Description" value:"State: falsepos;"`
`Description`	contains	`State: inactive;`	`excludes:Description` `field:"Description" value:"State: inactive;"`
`DeliveryAction`	match	`Blocked`	`excludes:DeliveryAction` `field:"DeliveryAction" value:"Blocked"`

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`Active`	eq	`true`	`field:"Active" kind:eq value:"true"`
`DomainName`	is_not_null	(no value, null check)	`field:"DomainName" kind:is_not_null`
`EmailEvents_TimeGenerated`	cross_field_compare	`ExpirationDateTime` transforms: `op:lt`	`field:"EmailEvents_TimeGenerated" kind:cross_field_compare value:"ExpirationDateTime"`
`RecipientEmailAddress`	is_not_null	(no value, null check)	`field:"RecipientEmailAddress" kind:is_not_null`
`SenderFromAddress`	is_not_null	(no value, null check)	`field:"SenderFromAddress" kind:is_not_null`
`TI_Domain`	in	`RecipientDomains` `SenderDomains`	`field:"TI_Domain" kind:in`

Output fields

These fields are emitted when the rule matches.

Field	Source
`ActivityGroupNames`	`project`
`ConfidenceLevel`	`project`
`ConfidenceScore`	`project`
`DeliveryAction`	`project`
`DeliveryLocation`	`project`
`Description`	`project`
`DomainName`	`project`
`EmailDirection`	`project`
`EmailEvents_TimeGenerated`	`project`
`ExpirationDateTime`	`project`
`IndicatorId`	`project`
`RecipientEmailAddress`	`project`
`SenderFromAddress`	`project`
`Subject`	`project`
`TI_Domain`	`project`
`ThreatType`	`project`
`TrafficLightProtocolLevel`	`project`
`Type`	`project`
`Url`	`project`
`Name`	`extend`
`UPNSuffix`	`extend`
`timestamp`	`extend`