splunk-security_content/docs/_posts/2021-02-12-detect_regsvcs_spawning_a_process.md

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title	excerpt	categories	last_modified_at	toc	toc_label	tags
Detect Regsvcs Spawning a Process	System Binary Proxy Execution , Regsvcs/Regasm	Endpoint	2021-02-12	true		System Binary Proxy Execution Regsvcs/Regasm Defense Evasion Defense Evasion Splunk Enterprise Splunk Enterprise Security Splunk Cloud Endpoint

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Description

The following analytic identifies regsvcs.exe spawning a process. This particular technique has been used in the wild to bypass application control products. Regasm.exe and Regsvcs.exe are signed by Microsoft. Spawning of a child process is rare from either process and should be investigated further. During investigation, identify and retrieve the content being loaded. Review parallel processes for additional suspicious behavior. Gather any other file modifications and review accordingly. regsvcs.exe and regasm.exe are natively found in C:\Windows\Microsoft.NET\Framework\v*\regasm|regsvcs.exe and C:\Windows\Microsoft.NET\Framework64\v*\regasm|regsvcs.exe.

• Type: TTP
• Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
• Datamodel: Endpoint- Datasource: Splunk Add-on for Sysmon
• Last Updated: 2021-02-12
• Author: Michael Haag, Splunk
• ID: bc477b57-5c21-4ab6-9c33-668772e7f114

Annotations

ATT&CK

ID	Technique	Tactic
T1218	System Binary Proxy Execution	Defense Evasion

| T1218.009 | Regsvcs/Regasm | Defense Evasion |

Kill Chain Phase

• Actions on Objectives

NIST

• PR.PT
• DE.CM

CIS20

• CIS 8

CVE

Search

| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime from datamodel=Endpoint.Processes where Processes.parent_process_name=regsvcs.exe by Processes.dest Processes.user Processes.parent_process Processes.process_name Processes.process Processes.process_id Processes.parent_process_id 
| `drop_dm_object_name(Processes)` 
| `security_content_ctime(firstTime)` 
| `security_content_ctime(lastTime)` 
| `detect_regsvcs_spawning_a_process_filter`

Macros

The SPL above uses the following Macros:

• security_content_ctime
• security_content_summariesonly

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

Required field

• _time
• Processes.parent_process_name
• Processes.dest
• Processes.user
• Processes.parent_process
• Processes.process_name
• Processes.process
• Processes.process_id
• Processes.parent_process_id

How To Implement

To successfully implement this search you need to be ingesting information on process that include the name of the process responsible for the changes from your endpoints into the Endpoint datamodel in the Processes node.

Known False Positives

Although unlikely, limited instances of regasm.exe or regsvcs.exe may cause a false positive. Filter based endpoint usage, command line arguments, or process lineage.

Associated Analytic story

• Suspicious Regsvcs Regasm Activity
• Living Off The Land

RBA

Risk Score	Impact	Confidence	Message
64.0	80	80	An instance of parent_process_name spawning process_name was identified on endpoint dest by user user typically not normal for this process.

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

Reference

• https://attack.mitre.org/techniques/T1218/009/
• https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1218.009/T1218.009.md
• https://lolbas-project.github.io/lolbas/Binaries/Regsvcs/

Test Dataset

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

• https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1218.009/atomic_red_team/windows-sysmon.log

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