TI map Domain entity to Web Session Events ASIM Web Session schema

let HAS_ANY_MAX = 10000;
let dt_lookBack = 1h;
let ioc_lookBack = 14d;
//Create a list of TLDs in our threat feed for later validation
let DOMAIN_TI=ThreatIntelligenceIndicator
// Picking up only IOC's that contain the entities we want
| where isnotempty(DomainName)
| where TimeGenerated >= ago(ioc_lookBack)
| summarize LatestIndicatorTime = arg_max(TimeGenerated, *) by IndicatorId
| where Active == true and ExpirationDateTime > now();
let DOMAIN_TI_list= todynamic(toscalar(DOMAIN_TI | summarize NIoCs = dcount(DomainName), Domains = make_set(DomainName) 
  | project Domains=iff(NIoCs > HAS_ANY_MAX, dynamic([]), Domains) ));
DOMAIN_TI
// 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 (
    _Im_WebSession(starttime=ago(dt_lookBack), url_has_any= DOMAIN_TI_list )
    //Extract domain patterns from syslog message
    | extend domain = tostring(parse_url(Url)["Host"])
    | where isnotempty(domain)
    | extend tld = tostring(split(domain, '.')[-1])
    | extend Event_TimeGenerated = TimeGenerated
) on $left.DomainName==$right.domain
| where Event_TimeGenerated < ExpirationDateTime
| summarize Event_TimeGenerated  = arg_max(Event_TimeGenerated , *) by IndicatorId, domain
| project Event_TimeGenerated, Description, ActivityGroupNames, IndicatorId, ThreatType, ExpirationDateTime, ConfidenceScore, domain, SrcIpAddr, Url   

id: b1832f60-6c3d-4722-a0a5-3d564ee61a63
description: |
    'This rule identifies Web Sessions for which the target URL hostname is a known IoC. This rule uses the [Advanced Security Information Model (ASIM)](https:/aka.ms/AboutASIM) and supports any web session source that complies with ASIM.'
requiredDataConnectors:
- connectorId: SquidProxy
  dataTypes:
  - SquidProxy_CL
- connectorId: Zscaler
  dataTypes:
  - CommonSecurityLog
- connectorId: ThreatIntelligence
  dataTypes:
  - ThreatIntelligenceIndicator
- connectorId: ThreatIntelligenceTaxii
  dataTypes:
  - ThreatIntelligenceIndicator
- connectorId: MicrosoftDefenderThreatIntelligence
  dataTypes:
  - ThreatIntelligenceIndicator
alertDetailsOverride:
  alertDisplayNameFormat: A web request from {{SrcIpAddr}} to hostname  {{domain}} matched an IoC
  alertDescriptionFormat: A client with address {{SrcIpAddr}} requested the URL {{Url}}, whose hostname is a known indicator of compromise of {{ThreatType}}. Consult the threat intelligence blade for more information on the indicator.
tactics:
- CommandAndControl
queryFrequency: 1h
queryPeriod: 14d
triggerOperator: gt
kind: Scheduled
query: |
  let HAS_ANY_MAX = 10000;
  let dt_lookBack = 1h;
  let ioc_lookBack = 14d;
  //Create a list of TLDs in our threat feed for later validation
  let DOMAIN_TI=ThreatIntelligenceIndicator
  // Picking up only IOC's that contain the entities we want
  | where isnotempty(DomainName)
  | where TimeGenerated >= ago(ioc_lookBack)
  | summarize LatestIndicatorTime = arg_max(TimeGenerated, *) by IndicatorId
  | where Active == true and ExpirationDateTime > now();
  let DOMAIN_TI_list= todynamic(toscalar(DOMAIN_TI | summarize NIoCs = dcount(DomainName), Domains = make_set(DomainName) 
    | project Domains=iff(NIoCs > HAS_ANY_MAX, dynamic([]), Domains) ));
  DOMAIN_TI
  // 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 (
      _Im_WebSession(starttime=ago(dt_lookBack), url_has_any= DOMAIN_TI_list )
      //Extract domain patterns from syslog message
      | extend domain = tostring(parse_url(Url)["Host"])
      | where isnotempty(domain)
      | extend tld = tostring(split(domain, '.')[-1])
      | extend Event_TimeGenerated = TimeGenerated
  ) on $left.DomainName==$right.domain
  | where Event_TimeGenerated < ExpirationDateTime
  | summarize Event_TimeGenerated  = arg_max(Event_TimeGenerated , *) by IndicatorId, domain
  | project Event_TimeGenerated, Description, ActivityGroupNames, IndicatorId, ThreatType, ExpirationDateTime, ConfidenceScore, domain, SrcIpAddr, Url     
customDetails:
  IndicatorId: IndicatorId
  ActivityGroupNames: ActivityGroupNames
  IoCExpirationTime: ExpirationDateTime
  EventTime: Event_TimeGenerated
  IoCConfidenceScore: ConfidenceScore
  IoCDescription: Description
  ThreatType: ThreatType
OriginalUri: https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Threat Intelligence/Analytic Rules/DomainEntity_imWebSession.yaml
version: 1.0.6
relevantTechniques:
- T1071
severity: Medium
name: TI map Domain entity to Web Session Events (ASIM Web Session schema)
entityMappings:
- fieldMappings:
  - identifier: Address
    columnName: SrcIpAddr
  entityType: IP
- fieldMappings:
  - identifier: Url
    columnName: Url
  entityType: URL
triggerThreshold: 0