Detection: Windows PowGoop Beacon Decoding

Description

Detects a DLL decoding and executing the PowGoop config.txt payload, the stage in the MuddyWater infection chain where an obfuscated PowerShell beacon is unwrapped and live C2 communication begins. PowGoop is the primary loader used by MuddyWater (also tracked as SeedWorm, Static Kitten, and MERCURY) and has been their main initial access loader since at least 2020. It abuses DLL side-loading against a fake GoogleUpdate.exe to execute a multi-stage decoding chain, a fully functional PowerShell backdoor disguised with a benign extension. The config.txt contains a hardcoded C2 address and victim GUID, beacons via modified base64-encoded HTTP, and runs C2 traffic under the legitimate Google Update process to evade network detection.

Search

 1
 2| tstats `security_content_summariesonly`
 3  count min(_time) as firstTime
 4        max(_time) as lastTime
 5
 6from datamodel=Endpoint.Processes where
 7
 8Processes.parent_process_path="*rundll32.exe"
 9Processes.process_name="powershell.exe"
10Processes.process="*FromBase64String*"
11Processes.process="*config.txt*"
12
13by Processes.process Processes.vendor_product Processes.user_id Processes.process_hash
14   Processes.parent_process_name Processes.parent_process_exec Processes.action
15   Processes.dest Processes.process_current_directory Processes.process_path
16   Processes.process_integrity_level Processes.original_file_name Processes.parent_process
17   Processes.parent_process_path Processes.parent_process_guid Processes.parent_process_id
18   Processes.process_guid Processes.process_id Processes.user Processes.process_name
19
20
21| `drop_dm_object_name(Processes)`
22
23| `security_content_ctime(firstTime)`
24
25| `security_content_ctime(lastTime)`
26
27| `windows_powgoop_beacon_decoding_filter`

Data Source

Name	Platform	Sourcetype	Source
CrowdStrike ProcessRollup2	Other	'crowdstrike:events:sensor'	'crowdstrike'
Sysmon EventID 1	Windows	'XmlWinEventLog'	'XmlWinEventLog:Microsoft-Windows-Sysmon/Operational'

Macros Used

Annotations

Default Configuration

This detection is configured by default in Splunk Enterprise Security to run with the following settings:

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

Some security tools or legitimate debugging processes may decode config files similar to PowGoop. Review and whitelist trusted applications to reduce false alerts.

Associated Analytic Story

• Compromised Windows Host

Risk Based Analytics (RBA)

Risk Message:

Potential PowGoop Beacon Decoding activity observed on $dest$ via $process$.

References

• https://www.cisa.gov/uscert/sites/default/files/publications/AA22-055A_Iranian_Government-Sponsored_Actors_Conduct_Cyber_Operations.pdf

Detection Testing

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