Detection: Suspicious microsoft workflow compiler usage

Updated Date: 2024-09-30 ID: 9bbc62e8-55d8-11eb-ae93-0242ac130002 Author: Michael Haag, Splunk Type: TTP Product: Splunk Enterprise Security

Description

The following analytic identifies the usage of microsoft.workflow.compiler.exe, a rarely utilized executable typically found in C:\Windows\Microsoft.NET\Framework64\v4.0.30319. This detection leverages data from Endpoint Detection and Response (EDR) agents, focusing on process execution telemetry. The significance of this activity lies in its uncommon usage, which may indicate malicious intent such as code execution or persistence mechanisms. If confirmed malicious, an attacker could leverage this process to execute arbitrary code, potentially leading to unauthorized access or further compromise of the system.

Search

1
2| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime from datamodel=Endpoint.Processes where `process_microsoftworkflowcompiler` by Processes.dest Processes.parent_process Processes.process_name Processes.original_file_name Processes.process Processes.user 
3| `drop_dm_object_name(Processes)` 
4| `security_content_ctime(firstTime)` 
5| `security_content_ctime(lastTime)` 
6| `suspicious_microsoft_workflow_compiler_usage_filter`

Data Source

Name	Platform	Sourcetype	Source
CrowdStrike ProcessRollup2	N/A	`'crowdstrike:events:sensor'`	`'crowdstrike'`
Sysmon EventID 1	Windows	`'xmlwineventlog'`	`'XmlWinEventLog:Microsoft-Windows-Sysmon/Operational'`
Windows Event Log Security 4688	Windows	`'xmlwineventlog'`	`'XmlWinEventLog:Security'`

Macros Used

Name	Value
process_microsoftworkflowcompiler	`(Processes.process_name=microsoft.workflow.compiler.exe OR Processes.original_file_name=Microsoft.Workflow.Compiler.exe)`
suspicious_microsoft_workflow_compiler_usage_filter	`search *`

suspicious_microsoft_workflow_compiler_usage_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
T1127	Trusted Developer Utilities Proxy Execution	Defense Evasion

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

The detection is based on data that originates from Endpoint Detection and Response (EDR) agents. These agents are designed to provide security-related telemetry from the endpoints where the agent is installed. To implement this search, you must ingest logs that contain the process GUID, process name, and parent process. Additionally, you must ingest complete command-line executions. These logs must be processed using the appropriate Splunk Technology Add-ons that are specific to the EDR product. The logs must also be mapped to the Processes node of the Endpoint data model. Use the Splunk Common Information Model (CIM) to normalize the field names and speed up the data modeling process.

Known False Positives

Although unlikely, limited instances have been identified coming from native Microsoft utilities similar to SCCM.

Associated Analytic Story

Risk Based Analytics (RBA)

Risk Message	Risk Score	Impact	Confidence
Suspicious microsoft.workflow.compiler.exe process ran on $dest$ by $user$	35	70	50

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: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: 4