Detection: Windows VSSVC Process Accessing Defender Engine

Updated Date: 2026-05-01 ID: 0c398be7-e33a-4882-9546-12166ceaf73c Author: Raven Tait, Splunk Type: TTP Product: Splunk Enterprise Security

Description

Detects vssvc.exe opening a handle to MsMpEng.exe. In the RedSun exploit, VSS participates in the cloud-file restore race that directs WD to write through the NTFS junction. This handle acquisition is observed at the exact moment of exploitation. vssvc querying MsMpEng is not expected in normal operation.

Search

 1`sysmon`
 2EventCode=10
 3TargetImage="*\\MsMpEng.exe"
 4SourceImage="*\\vssvc.exe"
 5
 6| stats count min(_time) as firstTime
 7              max(_time) as lastTime
 8  by EventID GrantedAccess Guid Opcode ProcessID
 9     SourceImage SourceProcessGUID  SourceProcessId
10     TargetImage TargetProcessGUID TargetProcessId
11     UserID dest CallTrace user_id parent_process_name
12     parent_process_guid process_name
13     process_guid process_id signature
14
15| `security_content_ctime(firstTime)`
16
17| `security_content_ctime(lastTime)`
18
19| `windows_vssvc_process_accessing_defender_engine_filter`

Data Source

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

Macros Used

Name	Value
sysmon	`(source=WinEventLog:Microsoft-Windows-Sysmon/Operational OR source=XmlWinEventLog:Microsoft-Windows-Sysmon/Operational OR source=Syslog:Linux-Sysmon/Operational)`
windows_vssvc_process_accessing_defender_engine_filter	`search *`

windows_vssvc_process_accessing_defender_engine_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
T1068	Exploitation for Privilege Escalation	Privilege Escalation

Exploitation

DE.CM

CIS 10

CVE

CVE-2026-33825

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

This search requires Sysmon Logs and a Sysmon configuration, which includes EventCode 10 for lsass.exe. This search uses an input macro named sysmon. We strongly recommend that you specify your environment-specific configurations (index, source, sourcetype, etc.) for Windows Sysmon logs. Replace the macro definition with configurations for your Splunk environment. The search also uses a post-filter macro designed to filter out known false positives.

Known False Positives

No false positives have been identified at this time.

Associated Analytic Story

Finding

Title	Entity Field	Entity Type	Risk Score
Windows Process $SourceImage$ accessing $TargetImage$ on $dest$	dest	system	50

References

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