Suspicious linking of existing user to external User

id: 22a320c2-e1e5-4c74-a35b-39fc9cdcf859
name: Suspicious linking of existing user to external User
description: |
  ' This query will detect when an attempt is made to update an existing user and link it to an guest or external identity. These activities are unusual and such linking of external 
  identities should be investigated. In some cases you may see internal Entra ID sync accounts (Sync_) do this which may be benign'
severity: Medium
requiredDataConnectors:
  - connectorId: AzureActiveDirectory
    dataTypes:
      - AuditLogs
queryFrequency: 1d
queryPeriod: 1d
triggerOperator: gt
triggerThreshold: 0
tactics:
  - PrivilegeEscalation
relevantTechniques:
  - T1078.004
tags:
  - GuestorExternalIdentities
query: |
  AuditLogs
  | where OperationName=~ "Update user" 
  | where Result =~ "success" 
  | mv-expand TargetResources 
  | mv-expand TargetResources.modifiedProperties 
  | extend displayName = tostring(TargetResources_modifiedProperties.displayName), 
  TargetUPN_oldValue = tostring(parse_json(tostring(TargetResources_modifiedProperties.oldValue))[0]), 
  TargetUPN_newValue = tostring(parse_json(tostring(TargetResources_modifiedProperties.newValue))[0])
  | where displayName == "UserPrincipalName" and TargetUPN_oldValue !has "#EXT" and TargetUPN_newValue has "#EXT"
  | extend InitiatingAppName = tostring(InitiatedBy.app.displayName)
  | extend InitiatingAppServicePrincipalId = tostring(InitiatedBy.app.servicePrincipalId)
  | extend InitiatingUserPrincipalName = tostring(InitiatedBy.user.userPrincipalName)
  | extend InitiatingAadUserId = tostring(InitiatedBy.user.id)
  | extend InitiatingIPAddress = tostring(InitiatedBy.user.ipAddress)
  | extend InitiatedBy = tostring(iff(isnotempty(InitiatingUserPrincipalName),InitiatingUserPrincipalName, InitiatingAppName))
  | summarize arg_max(TimeGenerated, *) by CorrelationId
  | project-reorder TimeGenerated, InitiatedBy, InitiatingAppName, InitiatingAppServicePrincipalId, InitiatingUserPrincipalName, InitiatingAadUserId, InitiatingIPAddress, TargetUPN_oldValue, TargetUPN_newValue
  | extend InitiatingAccountName = tostring(split(InitiatingUserPrincipalName, "@")[0]), InitiatingAccountUPNSuffix = tostring(split(InitiatingUserPrincipalName, "@")[1])
  | extend TargetAccountName = tostring(split(TargetUPN_oldValue, "@")[0]), TargetUPNSuffix = tostring(split(TargetUPN_oldValue, "@")[1])
entityMappings:
  - entityType: Account
    fieldMappings:
      - identifier: Name
        columnName: InitiatingAppName
      - identifier: AadUserId
        columnName: InitiatingAppServicePrincipalId
  - entityType: Account
    fieldMappings:
      - identifier: FullName
        columnName: InitiatingUserPrincipalName
      - identifier: Name
        columnName: InitiatingAccountName
      - identifier: UPNSuffix
        columnName: InitiatingAccountUPNSuffix
  - entityType: Account
    fieldMappings:
      - identifier: AadUserId
        columnName: InitiatingAadUserId
  - entityType: Account
    fieldMappings:
      - identifier: FullName
        columnName: TargetUPN_oldValue
      - identifier: Name
        columnName: TargetAccountName
      - identifier: UPNSuffix
        columnName: TargetUPNSuffix
  - entityType: IP
    fieldMappings:
      - identifier: Address
        columnName: InitiatingIPAddress
version: 1.1.0
kind: Scheduled
metadata:
    source:
        kind: Community
    author:
        name: Microsoft Security Research
    support:
        tier: Community
    categories:
        domains: [ "Security - Others", "Identity" ]