Fake computer account created

Back


Id	c1faf5e8-6958-11ec-90d6-0242ac120003
Rulename	Fake computer account created
Description	This query detects domain user accounts creation (event ID 4720) where the username ends with $. Accounts that end with $ are normally domain computer accounts and when they are created the event ID 4741 is generated instead. Ref: https://blog.menasec.net/2019/02/threat-hunting-6-hiding-in-plain-sights.html
Severity	Medium
Tactics	DefenseEvasion
Techniques	T1564
Required data connectors	SecurityEvents
Kind	Scheduled
Query frequency	1h
Query period	1h
Trigger threshold	0
Trigger operator	gt
Source Uri	https://github.com/Azure/Azure-Sentinel/blob/master/Detections/SecurityEvent/FakeComputerAccountCreated.yaml
Version	1.0.3
Arm template	c1faf5e8-6958-11ec-90d6-0242ac120003.json

KQL

SecurityEvent
| where EventID == 4720 and TargetUserName endswith "$"
| summarize StartTime = min(TimeGenerated), EndTime = max(TimeGenerated) by Computer, SubjectUserName, SubjectDomainName, SubjectAccount, SubjectUserSid, SubjectLogonId, 
TargetUserName, TargetDomainName, TargetAccount, TargetSid, UserPrincipalName
| extend HostName = tostring(split(Computer, ".")[0]), DomainIndex = toint(indexof(Computer, '.'))
| extend HostNameDomain = iff(DomainIndex != -1, substring(Computer, DomainIndex + 1), Computer)
| project-away DomainIndex

YAML

relevantTechniques:
- T1564
name: Fake computer account created
requiredDataConnectors:
- dataTypes:
  - SecurityEvent
  connectorId: SecurityEvents
entityMappings:
- fieldMappings:
  - identifier: FullName
    columnName: SubjectAccount
  - identifier: Name
    columnName: SubjectUserName
  - identifier: NTDomain
    columnName: SubjectDomainName
  entityType: Account
- fieldMappings:
  - identifier: Sid
    columnName: SubjectUserSid
  entityType: Account
- fieldMappings:
  - identifier: FullName
    columnName: TargetAccount
  - identifier: Name
    columnName: TargetUserName
  - identifier: NTDomain
    columnName: TargetDomainName
  entityType: Account
- fieldMappings:
  - identifier: Sid
    columnName: TargetSid
  entityType: Account
- fieldMappings:
  - identifier: FullName
    columnName: Computer
  - identifier: HostName
    columnName: HostName
  - identifier: DnsDomain
    columnName: HostNameDomain
  entityType: Host
triggerThreshold: 0
id: c1faf5e8-6958-11ec-90d6-0242ac120003
tactics:
- DefenseEvasion
version: 1.0.3
OriginalUri: https://github.com/Azure/Azure-Sentinel/blob/master/Detections/SecurityEvent/FakeComputerAccountCreated.yaml
queryPeriod: 1h
kind: Scheduled
metadata:
  categories:
    domains:
    - Security - Others
  author:
    name: Vasileios Paschalidis
  support:
    tier: Community
  source:
    kind: Community
queryFrequency: 1h
severity: Medium
description: |
  'This query detects domain user accounts creation (event ID 4720) where the username ends with $. 
  Accounts that end with $ are normally domain computer accounts and when they are created the event ID 4741 is generated instead.
  Ref: https://blog.menasec.net/2019/02/threat-hunting-6-hiding-in-plain-sights.html'  
query: |
  SecurityEvent
  | where EventID == 4720 and TargetUserName endswith "$"
  | summarize StartTime = min(TimeGenerated), EndTime = max(TimeGenerated) by Computer, SubjectUserName, SubjectDomainName, SubjectAccount, SubjectUserSid, SubjectLogonId, 
  TargetUserName, TargetDomainName, TargetAccount, TargetSid, UserPrincipalName
  | extend HostName = tostring(split(Computer, ".")[0]), DomainIndex = toint(indexof(Computer, '.'))
  | extend HostNameDomain = iff(DomainIndex != -1, substring(Computer, DomainIndex + 1), Computer)
  | project-away DomainIndex  
triggerOperator: gt

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/c1faf5e8-6958-11ec-90d6-0242ac120003')]",
      "kind": "Scheduled",
      "name": "[concat(parameters('workspace'),'/Microsoft.SecurityInsights/c1faf5e8-6958-11ec-90d6-0242ac120003')]",
      "properties": {
        "alertRuleTemplateName": "c1faf5e8-6958-11ec-90d6-0242ac120003",
        "customDetails": null,
        "description": "'This query detects domain user accounts creation (event ID 4720) where the username ends with $. \nAccounts that end with $ are normally domain computer accounts and when they are created the event ID 4741 is generated instead.\nRef: https://blog.menasec.net/2019/02/threat-hunting-6-hiding-in-plain-sights.html'\n",
        "displayName": "Fake computer account created",
        "enabled": true,
        "entityMappings": [
          {
            "entityType": "Account",
            "fieldMappings": [
              {
                "columnName": "SubjectAccount",
                "identifier": "FullName"
              },
              {
                "columnName": "SubjectUserName",
                "identifier": "Name"
              },
              {
                "columnName": "SubjectDomainName",
                "identifier": "NTDomain"
              }
            ]
          },
          {
            "entityType": "Account",
            "fieldMappings": [
              {
                "columnName": "SubjectUserSid",
                "identifier": "Sid"
              }
            ]
          },
          {
            "entityType": "Account",
            "fieldMappings": [
              {
                "columnName": "TargetAccount",
                "identifier": "FullName"
              },
              {
                "columnName": "TargetUserName",
                "identifier": "Name"
              },
              {
                "columnName": "TargetDomainName",
                "identifier": "NTDomain"
              }
            ]
          },
          {
            "entityType": "Account",
            "fieldMappings": [
              {
                "columnName": "TargetSid",
                "identifier": "Sid"
              }
            ]
          },
          {
            "entityType": "Host",
            "fieldMappings": [
              {
                "columnName": "Computer",
                "identifier": "FullName"
              },
              {
                "columnName": "HostName",
                "identifier": "HostName"
              },
              {
                "columnName": "HostNameDomain",
                "identifier": "DnsDomain"
              }
            ]
          }
        ],
        "OriginalUri": "https://github.com/Azure/Azure-Sentinel/blob/master/Detections/SecurityEvent/FakeComputerAccountCreated.yaml",
        "query": "SecurityEvent\n| where EventID == 4720 and TargetUserName endswith \"$\"\n| summarize StartTime = min(TimeGenerated), EndTime = max(TimeGenerated) by Computer, SubjectUserName, SubjectDomainName, SubjectAccount, SubjectUserSid, SubjectLogonId, \nTargetUserName, TargetDomainName, TargetAccount, TargetSid, UserPrincipalName\n| extend HostName = tostring(split(Computer, \".\")[0]), DomainIndex = toint(indexof(Computer, '.'))\n| extend HostNameDomain = iff(DomainIndex != -1, substring(Computer, DomainIndex + 1), Computer)\n| project-away DomainIndex\n",
        "queryFrequency": "PT1H",
        "queryPeriod": "PT1H",
        "severity": "Medium",
        "subTechniques": [],
        "suppressionDuration": "PT1H",
        "suppressionEnabled": false,
        "tactics": [
          "DefenseEvasion"
        ],
        "techniques": [
          "T1564"
        ],
        "templateVersion": "1.0.3",
        "triggerOperator": "GreaterThan",
        "triggerThreshold": 0
      },
      "type": "Microsoft.OperationalInsights/workspaces/providers/alertRules"
    }
  ]
}