Detection: Windows Handle Duplication in Known UAC-Bypass Binaries

Updated Date: 2025-10-31 ID: d7369bf5-1315-4138-b927-2dd8bb8c1da7 Author: Teoderick Contreras, Splunk Type: Anomaly Product: Splunk Enterprise Security

Description

The following analytic detects suspicious handle duplication activity targeting known Windows utilities such as ComputerDefaults.exe, Eventvwr.exe, and others. This technique is commonly used to escalate privileges or bypass UAC by inheriting or injecting elevated tokens or handles. The detection focuses on non-standard use of DuplicateHandle or token duplication where process, thread, or token handles are copied into the context of trusted, signed utilities. Such behavior may indicate attempts to execute with elevated rights without user consent. Alerts enable rapid triage using process trees, handle data, token attributes, command-lines, and binary hashes.

Search

1`sysmon` EventCode=10 TargetImage IN("*\\ComputerDefaults.exe", "*\\eventvwr.exe*", "*\\fodhelper.exe","*\\slui.exe","*\\sdclt.exe","*\\mmc.exe", "*\\colorcpl.exe","*\\wsreset.exe","*\\esentutl.exe", "*\PkgMgr.exe") AND NOT (SourceImage IN ("*C:\\Windows\\system32\\*","*C:\\Windows\\syswow64\\*","*C:\\Program Files\\*", "*C:\\Program Files (x86)\\*","%systemroot%\\*")) 
2| eval g_access_decimal = tonumber(replace(GrantedAccess,"0x",""),16) 
3| eval PROCESS_DUP_HANDLE = 64 
4| eval dup_handle_set = bit_and (g_access_decimal, PROCESS_DUP_HANDLE) 
5| where dup_handle_set == PROCESS_DUP_HANDLE 
6| stats count min(_time) as firstTime max(_time) as lastTime by SourceImage TargetImage GrantedAccess PROCESS_DUP_HANDLE g_access_decimal dup_handle_set Guid Opcode ProcessID SecurityID SourceProcessGUID SourceProcessId  TargetProcessGUID TargetProcessId UserID dest granted_access parent_process_exec parent_process_guid parent_process_id parent_process_name parent_process_path process_exec process_guid process_id process_name process_path signature signature_id user_id vendor_product CallTrace EventID 
7| `security_content_ctime(firstTime)` 
8| `security_content_ctime(lastTime)` 
9| `windows_handle_duplication_in_known_uac_bypass_binaries_filter`

Data Source

Name	Platform	Sourcetype	Source
Sysmon EventID 10	Windows	`'XmlWinEventLog'`	`'XmlWinEventLog:Microsoft-Windows-Sysmon/Operational'`

Macros Used

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

windows_handle_duplication_in_known_uac_bypass_binaries_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
T1134.001	Token Impersonation/Theft	Defense Evasion

Exploitation

DE.AE

CIS 10

FIN8

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 Risk Event	True

This configuration file applies to all detections of type anomaly. These detections will use Risk Based Alerting.

Implementation

To successfully implement this search, you must be ingesting data that records process activity from your hosts to populate the endpoint data model in the processes node. If you are using Sysmon, you must have at least version 6.0.4 of the Sysmon TA.

Known False Positives

It is possible legitimate applications will request access to list of know abused Windows UAC binaries process, filter as needed.

Associated Analytic Story

Castle RAT

Risk Based Analytics (RBA)

Risk Message:

A process $SourceImage$ is duplicating the handle token of $TargetImage$ on $dest$

Risk Object	Risk Object Type	Risk Score	Threat Objects
dest	system	20	parent_process_name

References

https://www.recordedfuture.com/research/from-castleloader-to-castlerat-tag-150-advances-operations

Detection Testing

Test Type	Status	Dataset	Source	Sourcetype
Validation	✅ Passing	N/A	N/A	N/A
Unit	✅ Passing	Dataset	`XmlWinEventLog:Microsoft-Windows-Sysmon/Operational`	`XmlWinEventLog`
Integration	✅ Passing	Dataset	`XmlWinEventLog:Microsoft-Windows-Sysmon/Operational`	`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