Detection: Windows Computer Account Created by Computer Account

Updated Date: 2024-05-20 ID: 97a8dc5f-8a7c-4fed-9e3e-ec407fd0268a Author: Michael Haag, Splunk Type: TTP Product: Splunk Enterprise Security

Description

The following analytic identifies a computer account creating a new computer account with a specific Service Principal Name (SPN) "RestrictedKrbHost". This detection leverages Windows Security Event Logs, specifically EventCode 4741, to identify such activities. This behavior is significant as it may indicate an attempt to establish unauthorized Kerberos authentication channels, potentially leading to lateral movement or privilege escalation. If confirmed malicious, this activity could allow an attacker to impersonate services, access sensitive information, or maintain persistence within the network.

Search

1`wineventlog_security` EventCode=4741 user_type=computer SubjectDomainName!="NT AUTHORITY" ServicePrincipalNames=*RestrictedKrbHost* 
2| stats  count min(_time) as firstTime max(_time) as lastTime by dest, subject, action ,src_user, user, user_type, SubjectUserName,SubjectDomainName 
3| `security_content_ctime(firstTime)` 
4| `security_content_ctime(lastTime)` 
5| `windows_computer_account_created_by_computer_account_filter`

Data Source

Name	Platform	Sourcetype	Source	Supported App
Windows Event Log Security 4741	Windows	`'xmlwineventlog'`	`'XmlWinEventLog:Security'`	N/A

Macros Used

Name	Value
security_content_ctime	`convert timeformat="%Y-%m-%dT%H:%M:%S" ctime($field$)`
windows_computer_account_created_by_computer_account_filter	`search *`

windows_computer_account_created_by_computer_account_filter is an empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Annotations

- MITRE ATT&CK

+ Kill Chain Phases

+ NIST

+ CIS

- Threat Actors

ID	Technique	Tactic
T1558	Steal or Forge Kerberos Tickets	Credential Access

KillChainPhase.EXPLOITAITON

NistCategory.DE_CM

Cis18Value.CIS_10

Default Configuration

This detection is configured by default in Splunk Enterprise Security to run with the following settings:

Setting	Value
Disabled	true
Cron Schedule	`0 * * * *`
Earliest Time	`-70m@m`
Latest Time	`-10m@m`
Schedule Window	`auto`
Creates Notable	Yes
Rule Title	`%name%`
Rule Description	`%description%`
Notable Event Fields	user, dest
Creates Risk Event	True

This configuration file applies to all detections of type TTP. These detections will use Risk Based Alerting and generate Notable Events.

Implementation

To successfully implement this search, you need to be ingesting Windows Security Event Logs with 4741 EventCode enabled. The Windows TA is also required.

Known False Positives

It is possible third party applications may have a computer account that adds computer accounts, filtering may be required.

Associated Analytic Story

Risk Based Analytics (RBA)

Risk Message	Risk Score	Impact	Confidence
A Computer Account on $dest$ created by a computer account (possibly indicative of Kerberos relay attack).	30	50	60

The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.

References

Detection Testing

Test Type	Status	Dataset	Source	Sourcetype
Validation	✅ Passing	N/A	N/A	N/A
Unit	✅ Passing	Dataset	`XmlWinEventLog:Security`	`XmlWinEventLog`
Integration	✅ Passing	Dataset	`XmlWinEventLog:Security`	`XmlWinEventLog`

Replay any dataset to Splunk Enterprise by using our replay.py tool or the UI. Alternatively you can replay a dataset into a Splunk Attack Range

Source: GitHub | Version: 3