Threat Connect TI map Domain entity to DnsEvents

// Define the lookback periods for time-based filters
let dt_lookBack = 1h; // Look back 1 hour for DNS events
let ioc_lookBack = 7d; // Look back 7 days for threat intelligence indicators
// Fetch threat intelligence indicators related to domains
let Domain_Indicators = ThreatIntelligenceIndicator
  | where TimeGenerated >= ago(ioc_lookBack)
  | summarize LatestIndicatorTime = arg_max(TimeGenerated, *) by IndicatorId
  | where ExpirationDateTime > now() and Active == true
  // Filter out non ThreatConnect TI Sources
  | where SourceSystem startswith "ThreatConnect-"
  // Filter out indicators without domain names
  | where isnotempty(DomainName)
  | extend TI_DomainEntity = DomainName;
// Create a list of TLDs in our threat feed for later validation
let maxListSize = 100000; // Define the maximum allowed size for each list
let list_tlds = Domain_Indicators
  | extend parts = split(DomainName, '.')
  | extend tld = parts[(array_length(parts)-1)]
  | summarize count() by tostring(tld)
  | project tld
  | summarize make_list(tld, maxListSize);
// Perform a join between domain indicators and DNS events to identify potential malicious activity
Domain_Indicators
  // Use innerunique to keep performance fast and result set low, as we only need one match to indicate potential malicious activity that needs investigation
  | join kind=innerunique (
    DnsEvents
    | where TimeGenerated > ago(dt_lookBack)
    // Extract domain patterns from syslog message
    | where isnotempty(Name)
    | extend parts = split(Name, '.')
    | extend tld = parts[(array_length(parts)-1)]
    // Validate parsed domain by checking if the TLD is in the list of TLDs in our threat feed
    | where tld in~ (list_tlds)
    | extend DNS_TimeGenerated = TimeGenerated
  ) on $left.TI_DomainEntity==$right.Name
  // Filter out DNS events that occurred after the expiration of the corresponding indicator
  | where DNS_TimeGenerated < ExpirationDateTime
  // Group the results by IndicatorId and Name, and keep the DNS event with the latest timestamp
  | summarize DNS_TimeGenerated = arg_max(DNS_TimeGenerated, *) by IndicatorId, Name
  // Select the desired output fields
  | project DNS_TimeGenerated, Description, ActivityGroupNames, IndicatorId, ThreatType, ExpirationDateTime, ConfidenceScore, Url, Computer, ClientIP, Name, QueryType, Type, TI_DomainEntity
  // Extract hostname and DNS domain from the Computer field
  | extend HostName = tostring(split(Computer, '.', 0)[0]), DnsDomain = tostring(strcat_array(array_slice(split(Computer, '.'), 1, -1), '.'))
  // Rename the timestamp field
  | extend timestamp = DNS_TimeGenerated

tactics:
- CommandAndControl
triggerOperator: gt
queryPeriod: 7d
queryFrequency: 1h
requiredDataConnectors:
- dataTypes:
  - DnsEvents
  connectorId: DNS
- dataTypes:
  - DnsEvents
  connectorId: ASimDnsActivityLogs
- dataTypes:
  - ThreatIntelligenceIndicator
  connectorId: ThreatIntelligence
- dataTypes:
  - ThreatIntelligenceIndicator
  connectorId: ThreatIntelligenceTaxii
- dataTypes:
  - ThreatIntelligenceIndicator
  connectorId: MicrosoftDefenderThreatIntelligence
id: f8960f1c-07d2-512b-9c41-952772d40c84
relevantTechniques:
- T1071
triggerThreshold: 0
kind: Scheduled
entityMappings:
- fieldMappings:
  - identifier: HostName
    columnName: HostName
  - identifier: DnsDomain
    columnName: DnsDomain
  entityType: Host
- fieldMappings:
  - identifier: Address
    columnName: ClientIP
  entityType: IP
- fieldMappings:
  - identifier: Url
    columnName: Url
  entityType: URL
query: |
  // Define the lookback periods for time-based filters
  let dt_lookBack = 1h; // Look back 1 hour for DNS events
  let ioc_lookBack = 7d; // Look back 7 days for threat intelligence indicators
  // Fetch threat intelligence indicators related to domains
  let Domain_Indicators = ThreatIntelligenceIndicator
    | where TimeGenerated >= ago(ioc_lookBack)
    | summarize LatestIndicatorTime = arg_max(TimeGenerated, *) by IndicatorId
    | where ExpirationDateTime > now() and Active == true
    // Filter out non ThreatConnect TI Sources
    | where SourceSystem startswith "ThreatConnect-"
    // Filter out indicators without domain names
    | where isnotempty(DomainName)
    | extend TI_DomainEntity = DomainName;
  // Create a list of TLDs in our threat feed for later validation
  let maxListSize = 100000; // Define the maximum allowed size for each list
  let list_tlds = Domain_Indicators
    | extend parts = split(DomainName, '.')
    | extend tld = parts[(array_length(parts)-1)]
    | summarize count() by tostring(tld)
    | project tld
    | summarize make_list(tld, maxListSize);
  // Perform a join between domain indicators and DNS events to identify potential malicious activity
  Domain_Indicators
    // Use innerunique to keep performance fast and result set low, as we only need one match to indicate potential malicious activity that needs investigation
    | join kind=innerunique (
      DnsEvents
      | where TimeGenerated > ago(dt_lookBack)
      // Extract domain patterns from syslog message
      | where isnotempty(Name)
      | extend parts = split(Name, '.')
      | extend tld = parts[(array_length(parts)-1)]
      // Validate parsed domain by checking if the TLD is in the list of TLDs in our threat feed
      | where tld in~ (list_tlds)
      | extend DNS_TimeGenerated = TimeGenerated
    ) on $left.TI_DomainEntity==$right.Name
    // Filter out DNS events that occurred after the expiration of the corresponding indicator
    | where DNS_TimeGenerated < ExpirationDateTime
    // Group the results by IndicatorId and Name, and keep the DNS event with the latest timestamp
    | summarize DNS_TimeGenerated = arg_max(DNS_TimeGenerated, *) by IndicatorId, Name
    // Select the desired output fields
    | project DNS_TimeGenerated, Description, ActivityGroupNames, IndicatorId, ThreatType, ExpirationDateTime, ConfidenceScore, Url, Computer, ClientIP, Name, QueryType, Type, TI_DomainEntity
    // Extract hostname and DNS domain from the Computer field
    | extend HostName = tostring(split(Computer, '.', 0)[0]), DnsDomain = tostring(strcat_array(array_slice(split(Computer, '.'), 1, -1), '.'))
    // Rename the timestamp field
    | extend timestamp = DNS_TimeGenerated  
OriginalUri: https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/ThreatConnect/Analytic Rules/ThreatConnect_DomainEntity_DnsEvents.yaml
name: Threat Connect TI map Domain entity to DnsEvents
version: 1.0.2
severity: Medium
description: |
    Identifies a match in DnsEvents from any ThreatConnect Domain IOC from TI