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Description

The following analytic identifies a suspicious PowerShell script execution via EventCode 4104 that contains multiple URLs within a function or array. This is typically found in obfuscated PowerShell or PowerShell executing embedded .NET or binary files that are attempting to download 2nd stage payloads. During triage, review parallel processes within the same timeframe. Review the full script block to identify other related artifacts.

  • Type: TTP

  • Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud

  • Last Updated: 2023-06-13
  • Author: Steven Dick
  • ID: 4a3f2a7d-6402-4e64-a76a-869588ec3b57

Annotations

ATT&CK

ATT&CK

ID Technique Tactic
T1059.001 PowerShell Execution
T1105 Ingress Tool Transfer Command And Control
Kill Chain Phase
  • Installation
  • Command and Control
NIST
  • DE.CM
CIS20
  • CIS 10
CVE 


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`powershell` EventCode=4104 ScriptBlockText IN ("*http:*","*https:*") 
| regex ScriptBlockText="(\"?(https?:\/\/(?:www\.)?[-a-zA-Z0-9@:%._\+~#=]{1,256}\.[a-zA-Z0-9()]{1,6}\b(?:[-a-zA-Z0-9()@:%_\+.~#?&\/=]*))\"?(?:,
|\))?){2,}" 
| rex max_match=20 field=ScriptBlockText "(?<url>https?:\/\/(?:www\.)?[-a-zA-Z0-9@:%._\+~#=]{1,256}\.[a-zA-Z0-9()]{1,6}\b(?:[-a-zA-Z0-9()@:%_\+.~#?&\/=]*))" 
| eval Path = case(isnotnull(Path),Path,true(),"unknown") 
| stats count min(_time) as firstTime max(_time) as lastTime list(ScriptBlockText) as command values(Path) as file_name values(UserID) as user values(url) as url dc(url) as url_count by ActivityID, Computer, EventCode 
| rename Computer as dest, EventCode as signature_id 
| `security_content_ctime(firstTime)` 
| `security_content_ctime(lastTime)` 
| `powershell_script_block_with_url_chain_filter`

Macros

The SPL above uses the following Macros:

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

Required fields

List of fields required to use this analytic.

  • _time
  • EventCode
  • ActivityID
  • Computer
  • ScriptBlockText

How To Implement

The following analytic requires PowerShell operational logs to be imported. Modify the powershell macro as needed to match the sourcetype or add index. This analytic is specific to 4104, or PowerShell Script Block Logging.

Known False Positives

Unknown, possible custom scripting.

Associated Analytic Story

RBA

Risk Score Impact Confidence Message
80.0 100 80 A suspicious powershell script used by $user$ on host $dest$ contains $url_count$ URLs in an array, this is commonly used for malware.

:information_source: 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

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

source | version: 1