Detection rules › Kusto

TI Map URL Entity to AuditLogs

Severity
medium
Time window
14d
Group by
IndicatorId, Url
Source
github.com/Azure/Azure-Sentinel

'This query identifies any URL indicators of compromise (IOCs) from threat intelligence (TI) by searching for matches in AuditLogs.'

MITRE ATT&CK coverage

TacticTechniques
Command & ControlT1071 Application Layer Protocol

Rule body kusto

id: 712fab52-2a7d-401e-a08c-ff939cc7c25e
name: TI Map URL Entity to AuditLogs
description: |
  'This query identifies any URL indicators of compromise (IOCs) from threat intelligence (TI) by searching for matches in AuditLogs.'
severity: Medium
requiredDataConnectors:
  - connectorId: AzureActiveDirectory
    dataTypes:
      - AuditLogs
  - connectorId: ThreatIntelligence
    dataTypes:
      - ThreatIntelligenceIndicator
  - connectorId: ThreatIntelligenceTaxii
    dataTypes:
      - ThreatIntelligenceIndicator
  - connectorId: MicrosoftDefenderThreatIntelligence
    dataTypes:
      - ThreatIntelligenceIndicator
queryFrequency: 1h
queryPeriod: 14d
triggerOperator: gt
triggerThreshold: 0
tactics:
  - CommandAndControl
relevantTechniques:
  - T1071
query: |
  let dt_lookBack = 1h;
  let ioc_lookBack = 14d;
  let AuditEvents = materialize(AuditLogs
    | where TimeGenerated >= ago(dt_lookBack)
    // Extract the URL that is contained within the JSON data
    | extend Url = extract("(http[s]?://(?:[a-zA-Z]|[0-9]|[$-_@.&+]|[!*\\(\\),]|(?:%[0-9a-fA-F][0-9a-fA-F]))+)", 1,tostring(TargetResources))
    | where isnotempty(Url)
    | extend userPrincipalName = tostring(parse_json(tostring(InitiatedBy.user)).userPrincipalName)
    | extend TargetResourceDisplayName = tostring(TargetResources[0].displayName)
    | extend Audit_TimeGenerated = TimeGenerated);
  let AuditUrls = AuditEvents | distinct Url = tolower(Url) | summarize make_list(Url);
  ThreatIntelligenceIndicator
  | where isnotempty(Url)
  | where TimeGenerated >= ago(ioc_lookBack)
  | where tolower(Url) in (AuditUrls)
  | 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;"
  // 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 (AuditEvents) on Url
  | where Audit_TimeGenerated < ExpirationDateTime
  | summarize Audit_TimeGenerated = arg_max(Audit_TimeGenerated, *) by IndicatorId, Url
  | project Audit_TimeGenerated, Description, ActivityGroupNames, IndicatorId, ThreatType, ExpirationDateTime, ConfidenceScore,
  OperationName, Identity, userPrincipalName, TargetResourceDisplayName, Url
  | extend AccountName = tostring(split(userPrincipalName, "@")[0]), AccountUPNSuffix = tostring(split(userPrincipalName, "@")[1])
  | extend HostName = tostring(split(TargetResourceDisplayName, ".")[0]), DomainIndex = toint(indexof(TargetResourceDisplayName, '.'))
  | extend HostNameDomain = iff(DomainIndex != -1, substring(TargetResourceDisplayName, DomainIndex + 1), TargetResourceDisplayName)
entityMappings:
  - entityType: Account
    fieldMappings:
      - identifier: FullName
        columnName: userPrincipalName
      - identifier: Name
        columnName: AccountName
      - identifier: UPNSuffix
        columnName: AccountUPNSuffix
  - entityType: Host
    fieldMappings:
      - identifier: FullName
        columnName: TargetResourceDisplayName
      - identifier: HostName
        columnName: HostName
      - identifier: DnsDomain
        columnName: HostNameDomain
  - entityType: URL
    fieldMappings:
      - identifier: Url
        columnName: Url
version: 1.2.8
kind: Scheduled

Stages and Predicates

Parameters

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

Let binding: AuditEvents

let AuditEvents = materialize(AuditLogs
  | where TimeGenerated >= ago(dt_lookBack)
  | extend Url = extract("(http[s]?://(?:[a-zA-Z]|[0-9]|[$-_@.&+]|[!*\\(\\),]|(?:%[0-9a-fA-F][0-9a-fA-F]))+)", 1,tostring(TargetResources))
  | where isnotempty(Url)
  | extend userPrincipalName = tostring(parse_json(tostring(InitiatedBy.user)).userPrincipalName)
  | extend TargetResourceDisplayName = tostring(TargetResources[0].displayName)
  | extend Audit_TimeGenerated = TimeGenerated);

Derived from dt_lookBack.

Let binding: AuditUrls

let AuditUrls = AuditEvents | distinct Url = tolower(Url) | summarize make_list(Url);

Derived from AuditEvents.

Stage 1: source

ThreatIntelligenceIndicator

Stage 2: where

| where isnotempty(Url)

Stage 3: where

| where TimeGenerated >= ago(ioc_lookBack)

Stage 4: where

| where tolower(Url) in (AuditUrls)

References AuditUrls (defined above).

Stage 5: summarize

| summarize LatestIndicatorTime = arg_max(TimeGenerated, *) by IndicatorId

Stage 6: where

| where Active == true and ExpirationDateTime > now()

Stage 7: where

| where Description !contains_cs "State: inactive;" and Description !contains_cs "State: falsepos;"

Stage 8: join

| join kind=innerunique (AuditEvents) on Url

Stage 9: where

| where Audit_TimeGenerated < ExpirationDateTime

Stage 10: summarize

| summarize Audit_TimeGenerated = arg_max(Audit_TimeGenerated, *) by IndicatorId, Url

Stage 11: project

| project Audit_TimeGenerated, Description, ActivityGroupNames, IndicatorId, ThreatType, ExpirationDateTime, ConfidenceScore,
OperationName, Identity, userPrincipalName, TargetResourceDisplayName, Url

Stage 12: extend (3 consecutive steps)

| extend AccountName = tostring(split(userPrincipalName, "@")[0]), AccountUPNSuffix = tostring(split(userPrincipalName, "@")[1])
| extend HostName = tostring(split(TargetResourceDisplayName, ".")[0]), DomainIndex = toint(indexof(TargetResourceDisplayName, '.'))
| extend HostNameDomain = iff(DomainIndex != -1, substring(TargetResourceDisplayName, DomainIndex + 1), TargetResourceDisplayName)

Exclusions

Top-level NOT(...) conjuncts: predicates this rule actively suppresses.

FieldKindExcluded values
DescriptioncontainsState: falsepos;
DescriptioncontainsState: inactive;

Indicators

Each row is a field, operator, and value that the rule matches. The corpus column counts how many other rules in the catalog look for the same combination: high numbers point to widely-used, community-vetted indicators. Blank or 1 shows that the indicator is specific to this rule.

FieldKindValues
Activeeq
  • true transforms: cased
Audit_TimeGeneratedlt
  • ExpirationDateTime transforms: cased
Urlin
  • AuditUrls transforms: tolower, cased
Urlis_not_null
  • (no value, null check)

Output fields

Fields the rule emits when it matches. Chronicle authors list these in the outcome block; they appear on the detection and $risk_score drives alerting. Sentinel / Defender XDR rules build them up through project / summarize / extend stages. Sentinel maps these into alert fields via entityMappings and customDetails; Defender XDR custom detections surface them as alert fields directly.

FieldSource
ActivityGroupNamesproject
Audit_TimeGeneratedproject
ConfidenceScoreproject
Descriptionproject
ExpirationDateTimeproject
Identityproject
IndicatorIdproject
OperationNameproject
TargetResourceDisplayNameproject
ThreatTypeproject
Urlproject
userPrincipalNameproject
AccountNameextend
AccountUPNSuffixextend
DomainIndexextend
HostNameextend
HostNameDomainextend