Powershell Processing Stream Of Data

name: Powershell Processing Stream Of Data
id: 0d718b52-c9f1-11eb-bc61-acde48001122
version: 19
creation_date: '2021-06-14'
modification_date: '2026-06-29'
author: Teoderick Contreras, Splunk
status: production
type: Anomaly
description: |-
    The following analytic detects suspicious PowerShell script execution involving compressed stream data processing, identified via EventCode 4104.
    It leverages PowerShell Script Block Logging to flag scripts using `IO.Compression`, `IO.StreamReader`, or decompression methods.
    This activity is significant as it often indicates obfuscated PowerShell or embedded .NET/binary execution, which are common tactics for evading detection.
    If confirmed malicious, this behavior could allow attackers to execute hidden code, escalate privileges, or maintain persistence within the environment.
data_source:
    - Powershell Script Block Logging 4104
search: |-
    `powershell`
    EventCode=4104
    ScriptBlockText IN (
        "*IO.Compression.*",
        "*IO.StreamReader*",
        "*]::Decompress*"
    )
    | fillnull
    | stats count min(_time) as firstTime
                  max(_time) as lastTime
      by dest signature signature_id
         user_id vendor_product EventID
         Guid Opcode Name
         Path ProcessID ScriptBlockId
         ScriptBlockText
      | `security_content_ctime(firstTime)`
      | `security_content_ctime(lastTime)`
      | `powershell_processing_stream_of_data_filter`
how_to_implement: To successfully implement this analytic, you will need to enable PowerShell Script Block Logging on some or all endpoints. Additional setup here https://help.splunk.com/en/security-offerings/splunk-user-behavior-analytics/get-data-in/5.4.1/add-other-data-to-splunk-uba/configure-powershell-logging-to-see-powershell-anomalies-in-splunk-uba.
known_false_positives: powershell may used this function to process compressed data.
references:
    - https://medium.com/@ahmedjouini99/deobfuscating-emotets-powershell-payload-e39fb116f7b9
    - https://help.splunk.com/en/security-offerings/splunk-user-behavior-analytics/get-data-in/5.4.1/add-other-data-to-splunk-uba/configure-powershell-logging-to-see-powershell-anomalies-in-splunk-uba
    - https://blog.palantir.com/tampering-with-windows-event-tracing-background-offense-and-defense-4be7ac62ac63
    - https://static1.squarespace.com/static/552092d5e4b0661088167e5c/t/59c1814829f18782e24f1fe2/1505853768977/Windows+PowerShell+Logging+Cheat+Sheet+ver+Sept+2017+v2.1.pdf
    - https://www.crowdstrike.com/blog/investigating-powershell-command-and-script-logging/
    - https://www.splunk.com/en_us/blog/security/hunting-for-malicious-powershell-using-script-block-logging.html
    - https://thedfirreport.com/2023/05/22/icedid-macro-ends-in-nokoyawa-ransomware/
intermediate_findings:
    entities:
        - field: dest
          type: system
          score: 20
          message: A suspicious powershell script with the ScriptBlockId [$ScriptBlockId$] containing stream commands to process compressed or decompressed binary file was executed on host $dest$
analytic_story:
    - Hellcat Ransomware
    - Malicious PowerShell
    - Medusa Ransomware
    - PXA Stealer
    - Data Destruction
    - Braodo Stealer
    - AsyncRAT
    - Hermetic Wiper
    - IcedID
    - XWorm
    - MoonPeak
    - MuddyWater
    - Salat Stealer
asset_type: Endpoint
mitre_attack_id:
    - T1059.001
product:
    - Splunk Enterprise
    - Splunk Enterprise Security
    - Splunk Cloud
category: endpoint
security_domain: endpoint