Detection: Windows Builtin Account Name Was Changed

Updated Date: 2026-08-24 ID: 65e6e8b9-c68c-460f-beb8-48cfe91b4d21 Author: Raven Tait, Splunk Type: TTP Product: Splunk Enterprise Security

Description

The following analytic detects renaming of Windows built-in accounts via Event ID 4781. It identifies renames targeting accounts with well-known reserved RIDs (500-504): Administrator, Guest, krbtgt, DefaultAccount, and WDAGUtilityAccount, by matching the TargetSid field against the S-1-5-21-*-50[0-4] pattern. Attackers commonly rename the built-in Administrator account to evade detections that alert on the literal account name, while retaining the full privileges of the RID-500 account. Renaming Guest, krbtgt, or other reserved accounts is highly unusual in any legitimate environment.

Search

 1`wineventlog_security`
 2EventCode=4781
 3TargetSid="S-1-5-21-*"
 4
 5
 6| where match(TargetSid, "S-1-5-21-.*-50[0-4]$")
 7
 8
 9| stats count min(_time) as firstTime
10              max(_time) as lastTime
11  by dest OldTargetUserName NewTargetUserName
12     TargetSid SubjectLogonId
13
14
15| `security_content_ctime(firstTime)`
16
17| `security_content_ctime(lastTime)`
18
19| `windows_builtin_account_name_was_changed_filter`

Data Source

Name	Platform	Sourcetype	Source
Windows Event Log Security 4781	Windows	`'XmlWinEventLog'`	`'XmlWinEventLog:Security'`

Macros Used

Name	Value
wineventlog_security	`eventtype="wineventlog_security" OR Channel="security" OR source="XmlWinEventLog:Security" OR source="WinEventLog:Security"`
windows_builtin_account_name_was_changed_filter	`search *`

windows_builtin_account_name_was_changed_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
T1036.010	Masquerade Account Name	Stealth
T1078.003	Local Accounts	Initial Access

Exploitation

Delivery

Installation

DE.CM

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 Finding (Notable)	Yes
Rule Title	`%name%`
Rule Description	`%description%`
Notable Event Fields	user, dest
Creates Intermediate Finding (Risk Event)	No

TTP detections generate a Finding (Notable) and may generate Intermediate Findings (Risk Events) for associated entities.

Implementation

To successfully implement this search, you need to be ingesting Windows event logs from your hosts. In addition, the Splunk Windows TA is needed.

Known False Positives

Renaming built-in accounts is uncommon in most environments but may occur during initial system hardening or CIS benchmark compliance efforts. Validate the source user, logon ID, and timing against expected change control windows before tuning.

Associated Analytic Story

Finding

Title	Entity Field	Entity Type	Risk Score
Built-in account [$OldTargetUserName$] (SID [$TargetSid$]) was renamed to [$NewTargetUserName$] on [$dest$]	dest	system	50

Threat Objects

Field	Type
NewTargetUserName	user

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: 1