Suspicious linking of existing user to external User | Microsoft Sentinel Analytic Rules

Back


Id	22a320c2-e1e5-4c74-a35b-39fc9cdcf859
Rulename	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
Tactics	PrivilegeEscalation
Techniques	T1078.004
Required data connectors	AzureActiveDirectory
Kind	Scheduled
Query frequency	1d
Query period	1d
Trigger threshold	0
Trigger operator	gt
Source Uri	https://github.com/Azure/Azure-Sentinel/blob/master/Detections/AuditLogs/SuspiciousLinkingofExternalIdtoExistingUsers.yaml
Version	1.1.0
Arm template	22a320c2-e1e5-4c74-a35b-39fc9cdcf859.json

KQL

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])

YAML

entityMappings:
- entityType: Account
  fieldMappings:
  - columnName: InitiatingAppName
    identifier: Name
  - columnName: InitiatingAppServicePrincipalId
    identifier: AadUserId
- entityType: Account
  fieldMappings:
  - columnName: InitiatingUserPrincipalName
    identifier: FullName
  - columnName: InitiatingAccountName
    identifier: Name
  - columnName: InitiatingAccountUPNSuffix
    identifier: UPNSuffix
- entityType: Account
  fieldMappings:
  - columnName: InitiatingAadUserId
    identifier: AadUserId
- entityType: Account
  fieldMappings:
  - columnName: TargetUPN_oldValue
    identifier: FullName
  - columnName: TargetAccountName
    identifier: Name
  - columnName: TargetUPNSuffix
    identifier: UPNSuffix
- entityType: IP
  fieldMappings:
  - columnName: InitiatingIPAddress
    identifier: Address
tactics:
- PrivilegeEscalation
queryPeriod: 1d
queryFrequency: 1d
requiredDataConnectors:
- connectorId: AzureActiveDirectory
  dataTypes:
  - AuditLogs
severity: Medium
relevantTechniques:
- T1078.004
name: Suspicious linking of existing user to external User
metadata:
  support:
    tier: Community
  author:
    name: Microsoft Security Research
  source:
    kind: Community
  categories:
    domains:
    - Security - Others
    - Identity
kind: Scheduled
OriginalUri: https://github.com/Azure/Azure-Sentinel/blob/master/Detections/AuditLogs/SuspiciousLinkingofExternalIdtoExistingUsers.yaml
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'
triggerOperator: gt
id: 22a320c2-e1e5-4c74-a35b-39fc9cdcf859
version: 1.1.0
triggerThreshold: 0
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])

ARM

{
  "$schema": "https://schema.management.azure.com/schemas/2019-04-01/deploymentTemplate.json#",
  "contentVersion": "1.0.0.0",
  "parameters": {
    "workspace": {
      "type": "String"
    }
  },
  "resources": [
    {
      "apiVersion": "2024-01-01-preview",
      "id": "[concat(resourceId('Microsoft.OperationalInsights/workspaces/providers', parameters('workspace'), 'Microsoft.SecurityInsights'),'/alertRules/22a320c2-e1e5-4c74-a35b-39fc9cdcf859')]",
      "kind": "Scheduled",
      "name": "[concat(parameters('workspace'),'/Microsoft.SecurityInsights/22a320c2-e1e5-4c74-a35b-39fc9cdcf859')]",
      "properties": {
        "alertRuleTemplateName": "22a320c2-e1e5-4c74-a35b-39fc9cdcf859",
        "customDetails": null,
        "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 \nidentities should be investigated. In some cases you may see internal Entra ID sync accounts (Sync_) do this which may be benign'\n",
        "displayName": "Suspicious linking of existing user to external User",
        "enabled": true,
        "entityMappings": [
          {
            "entityType": "Account",
            "fieldMappings": [
              {
                "columnName": "InitiatingAppName",
                "identifier": "Name"
              },
              {
                "columnName": "InitiatingAppServicePrincipalId",
                "identifier": "AadUserId"
              }
            ]
          },
          {
            "entityType": "Account",
            "fieldMappings": [
              {
                "columnName": "InitiatingUserPrincipalName",
                "identifier": "FullName"
              },
              {
                "columnName": "InitiatingAccountName",
                "identifier": "Name"
              },
              {
                "columnName": "InitiatingAccountUPNSuffix",
                "identifier": "UPNSuffix"
              }
            ]
          },
          {
            "entityType": "Account",
            "fieldMappings": [
              {
                "columnName": "InitiatingAadUserId",
                "identifier": "AadUserId"
              }
            ]
          },
          {
            "entityType": "Account",
            "fieldMappings": [
              {
                "columnName": "TargetUPN_oldValue",
                "identifier": "FullName"
              },
              {
                "columnName": "TargetAccountName",
                "identifier": "Name"
              },
              {
                "columnName": "TargetUPNSuffix",
                "identifier": "UPNSuffix"
              }
            ]
          },
          {
            "entityType": "IP",
            "fieldMappings": [
              {
                "columnName": "InitiatingIPAddress",
                "identifier": "Address"
              }
            ]
          }
        ],
        "OriginalUri": "https://github.com/Azure/Azure-Sentinel/blob/master/Detections/AuditLogs/SuspiciousLinkingofExternalIdtoExistingUsers.yaml",
        "query": "AuditLogs\n| where OperationName=~ \"Update user\" \n| where Result =~ \"success\" \n| mv-expand TargetResources \n| mv-expand TargetResources.modifiedProperties \n| extend displayName = tostring(TargetResources_modifiedProperties.displayName), \nTargetUPN_oldValue = tostring(parse_json(tostring(TargetResources_modifiedProperties.oldValue))[0]), \nTargetUPN_newValue = tostring(parse_json(tostring(TargetResources_modifiedProperties.newValue))[0])\n| where displayName == \"UserPrincipalName\" and TargetUPN_oldValue !has \"#EXT\" and TargetUPN_newValue has \"#EXT\"\n| extend InitiatingAppName = tostring(InitiatedBy.app.displayName)\n| extend InitiatingAppServicePrincipalId = tostring(InitiatedBy.app.servicePrincipalId)\n| extend InitiatingUserPrincipalName = tostring(InitiatedBy.user.userPrincipalName)\n| extend InitiatingAadUserId = tostring(InitiatedBy.user.id)\n| extend InitiatingIPAddress = tostring(InitiatedBy.user.ipAddress)\n| extend InitiatedBy = tostring(iff(isnotempty(InitiatingUserPrincipalName),InitiatingUserPrincipalName, InitiatingAppName))\n| summarize arg_max(TimeGenerated, *) by CorrelationId\n| project-reorder TimeGenerated, InitiatedBy, InitiatingAppName, InitiatingAppServicePrincipalId, InitiatingUserPrincipalName, InitiatingAadUserId, InitiatingIPAddress, TargetUPN_oldValue, TargetUPN_newValue\n| extend InitiatingAccountName = tostring(split(InitiatingUserPrincipalName, \"@\")[0]), InitiatingAccountUPNSuffix = tostring(split(InitiatingUserPrincipalName, \"@\")[1])\n| extend TargetAccountName = tostring(split(TargetUPN_oldValue, \"@\")[0]), TargetUPNSuffix = tostring(split(TargetUPN_oldValue, \"@\")[1])\n",
        "queryFrequency": "P1D",
        "queryPeriod": "P1D",
        "severity": "Medium",
        "subTechniques": [
          "T1078.004"
        ],
        "suppressionDuration": "PT1H",
        "suppressionEnabled": false,
        "tactics": [
          "PrivilegeEscalation"
        ],
        "tags": [
          "GuestorExternalIdentities"
        ],
        "techniques": [
          "T1078"
        ],
        "templateVersion": "1.1.0",
        "triggerOperator": "GreaterThan",
        "triggerThreshold": 0
      },
      "type": "Microsoft.OperationalInsights/workspaces/providers/alertRules"
    }
  ]
}