TI Map Email entity to EmailEvents

Severity: medium
Time window: 14d
Group by: Id, ObservableValue, RecipientEmailAddress, SenderFromAddress, TI_EmailAddress
Source: github.com/Azure/Azure-Sentinel

Identifies a match in EmailEvents table from any Email 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: 18b61c3f-55fa-4eb9-8721-72dabd1eb3cb
name: TI Map Email entity to EmailEvents
description: |
  'Identifies a match in EmailEvents table from any Email IOC from TI'
severity: Medium
requiredDataConnectors:
  - connectorId: MicrosoftThreatProtection
    dataTypes:
      - EmailEvents
  - connectorId: ThreatIntelligence
    dataTypes:
      - ThreatIntelIndicators
  - connectorId: ThreatIntelligenceTaxii
    dataTypes:
      - ThreatIntelIndicators
  - connectorId: MicrosoftDefenderThreatIntelligence
    dataTypes:
      - ThreatIntelIndicators
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 SenderFromAddress = tolower(SenderFromAddress) | extend RecipientEmailAddress = tolower(RecipientEmailAddress));
  let SenderAddresses = EmailEvents_ | distinct  SenderFromAddress | summarize make_list(SenderFromAddress);
  let RecipientAddresses = EmailEvents_ | distinct  RecipientEmailAddress | summarize make_list(RecipientEmailAddress);
  let TI = materialize(ThreatIntelIndicators
  | where TimeGenerated >= ago(ioc_lookBack)
  | extend IndicatorType = replace(@"\[|\]|\""", "", tostring(split(ObservableKey, ":", 0)))
  | where 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)
  | extend TI_EmailAddress = tolower(EmailSenderAddress)
  | where TI_EmailAddress in (SenderAddresses) or TI_EmailAddress in (RecipientAddresses)
  | summarize LatestIndicatorTime = arg_max(TimeGenerated, *) by Id, ObservableValue
  | where IsActive and (ValidUntil > now() or isempty(ValidUntil)));
  (union
    (TI | join kind=innerunique (EmailEvents_) on $left.TI_EmailAddress == $right.SenderFromAddress),
    (TI | join kind=innerunique (EmailEvents_) on $left.TI_EmailAddress == $right.RecipientEmailAddress))
  | where EmailEvents_TimeGenerated < ValidUntil
  | extend Description = tostring(parse_json(Data).description)
  | extend ActivityGroupNames = extract("ActivityGroup:([^,]+)", 1, tostring(parse_json(Data).labels))
  | summarize EmailEvents_TimeGenerated = arg_max(EmailEvents_TimeGenerated, *) by Id, TI_EmailAddress
  | extend DomainName = EmailSourceDomain
  | extend Url = DomainName
  | project EmailEvents_TimeGenerated, Description, ActivityGroupNames, Id, ValidUntil, Confidence, DomainName, RecipientEmailAddress, SenderFromAddress, Subject, ConfidenceLevel, Url, Type, TI_EmailAddress, TrafficLightProtocolLevel, DeliveryAction, DeliveryLocation, EmailDirection
  | extend Name = tostring(split(RecipientEmailAddress, '@', 0)[0]), UPNSuffix = tostring(split(RecipientEmailAddress, '@', 1)[0])
  | extend timestamp = EmailEvents_TimeGenerated
  | project-reorder *, TrafficLightProtocolLevel, DomainName, Type, TI_EmailAddress
entityMappings:
  - entityType: Account
    fieldMappings:
      - identifier: FullName
        columnName: RecipientEmailAddress
      - identifier: Name
        columnName: Name
      - identifier: UPNSuffix
        columnName: UPNSuffix
version: 1.0.6
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 SenderFromAddress = tolower(SenderFromAddress) | extend RecipientEmailAddress = tolower(RecipientEmailAddress));

Let binding: `SenderAddresses`

let SenderAddresses = EmailEvents_ | distinct  SenderFromAddress | summarize make_list(SenderFromAddress);

Let binding: `RecipientAddresses`

let RecipientAddresses = EmailEvents_ | distinct  RecipientEmailAddress | summarize make_list(RecipientEmailAddress);

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_EmailAddress == $right.SenderFromAddress

Leg 2: `TI`

TI | join kind=innerunique (EmailEvents_) on $left.TI_EmailAddress == $right.RecipientEmailAddress

Applied to the combined result

| where EmailEvents_TimeGenerated < ValidUntil
| extend Description = tostring(parse_json(Data).description)
| extend ActivityGroupNames = extract("ActivityGroup:([^,]+)", 1, tostring(parse_json(Data).labels))
| summarize EmailEvents_TimeGenerated = arg_max(EmailEvents_TimeGenerated, *) by Id, TI_EmailAddress
| extend DomainName = EmailSourceDomain
| extend Url = DomainName
| project EmailEvents_TimeGenerated, Description, ActivityGroupNames, Id, ValidUntil, Confidence, DomainName, RecipientEmailAddress, SenderFromAddress, Subject, ConfidenceLevel, Url, Type, TI_EmailAddress, TrafficLightProtocolLevel, DeliveryAction, DeliveryLocation, EmailDirection
| extend Name = tostring(split(RecipientEmailAddress, '@', 0)[0]), UPNSuffix = tostring(split(RecipientEmailAddress, '@', 1)[0])
| extend timestamp = EmailEvents_TimeGenerated
| project-reorder *, TrafficLightProtocolLevel, DomainName, Type, TI_EmailAddress

Exclusions

The rule actively suppresses these predicates.

Field	Kind	Excluded values	Search
`DeliveryAction`	match	`Blocked`	`excludes:DeliveryAction` `field:"DeliveryAction" value:"Blocked"`

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`EmailEvents_TimeGenerated`	cross_field_compare	`ValidUntil` transforms: `op:lt`	`field:"EmailEvents_TimeGenerated" kind:cross_field_compare value:"ValidUntil"`
`IndicatorType`	eq	`email-addr`	`field:"IndicatorType" kind:eq value:"email-addr"`
`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_EmailAddress`	in	`RecipientAddresses` `SenderAddresses`	`field:"TI_EmailAddress" kind:in`
`ValidUntil`	is_null	(no value, null check)	`field:"ValidUntil" kind:is_null`

Output fields

These fields are emitted when the rule matches.

Field	Source
`ActivityGroupNames`	`project`
`Confidence`	`project`
`ConfidenceLevel`	`project`
`DeliveryAction`	`project`
`DeliveryLocation`	`project`
`Description`	`project`
`DomainName`	`project`
`EmailDirection`	`project`
`EmailEvents_TimeGenerated`	`project`
`Id`	`project`
`RecipientEmailAddress`	`project`
`SenderFromAddress`	`project`
`Subject`	`project`
`TI_EmailAddress`	`project`
`TrafficLightProtocolLevel`	`project`
`Type`	`project`
`Url`	`project`
`ValidUntil`	`project`
`Name`	`extend`
`UPNSuffix`	`extend`
`timestamp`	`extend`