Malicious PowerShell Process - Encoded Command

SPLUNK detection rule by David Dorsey, Michael Haag, Splunk, SirDuckly, GitHub Community · Apache-2.0

The following analytic detects the use of the EncodedCommand parameter in PowerShell processes. It leverages Endpoint Detection and Response (EDR) data to identify variations of the EncodedCommand parameter, including shortened forms and different command switch types. This activity can be significant because adversaries often use encoded commands to obfuscate malicious scripts, making detection harder. If confirmed malicious, this behavior could allow attackers to execute hidden code, potentially leading to unauthorized access, privilege escalation, or persistent threats within the environment. Review parallel events to determine legitimacy and tune based on known administrative scripts.

name: Malicious PowerShell Process - Encoded Command
id: c4db14d9-7909-48b4-a054-aa14d89dbb19
version: 21
creation_date: '2020-04-29'
modification_date: '2026-05-13'
author: David Dorsey, Michael Haag, Splunk, SirDuckly, GitHub Community
status: production
type: Hunting
description: |
    The following analytic detects the use of the EncodedCommand parameter in PowerShell processes.
    It leverages Endpoint Detection and Response (EDR) data to identify variations of the EncodedCommand parameter, including shortened forms and different command switch types.
    This activity can be significant because adversaries often use encoded commands to obfuscate malicious scripts, making detection harder.
    If confirmed malicious, this behavior could allow attackers to execute hidden code, potentially leading to unauthorized access, privilege escalation, or persistent threats within the environment.
    Review parallel events to determine legitimacy and tune based on known administrative scripts.
data_source:
    - Sysmon EventID 1
    - Windows Event Log Security 4688
    - CrowdStrike ProcessRollup2
search: |-
    | tstats `security_content_summariesonly`
      count min(_time) as firstTime
            max(_time) as lastTime
    from datamodel=Endpoint.Processes where
    `process_powershell`
    by Processes.action Processes.dest Processes.original_file_name
       Processes.parent_process Processes.parent_process_exec
       Processes.parent_process_guid Processes.parent_process_id
       Processes.parent_process_name Processes.parent_process_path
       Processes.process Processes.process_exec Processes.process_guid
       Processes.process_hash Processes.process_id
       Processes.process_integrity_level Processes.process_name
       Processes.process_path Processes.user
       Processes.user_id Processes.vendor_product
    | `drop_dm_object_name(Processes)`
    | `security_content_ctime(firstTime)`
    | `security_content_ctime(lastTime)`
    | where match(process,"(?i)(?:^|\\s)(?:/(?!/)|--?|–{1,2}|—{1,2}|―{1,2})(?:ec|encodedcommand|encodedcomman|encodedcomma|encodedcomm|encodedcom|encodedco|encodedc|encoded|encode|encod|enco|enc|en|e(?=\\s))\\s+['\\\"]?[A-Za-z0-9+/=]{5,}['\\\"]?")
    | `malicious_powershell_process___encoded_command_filter`
how_to_implement: |
    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: |
    False positives are expected from legitimate PowerShell scripts,
    system administrators, and applications. Filter as needed.
references:
    - https://regexr.com/662ov
    - https://github.com/redcanaryco/AtomicTestHarnesses/blob/master/Windows/TestHarnesses/T1059.001_PowerShell/OutPowerShellCommandLineParameter.ps1
    - https://ss64.com/ps/powershell.html
    - https://twitter.com/M_haggis/status/1440758396534214658?s=20
    - https://www.microsoft.com/security/blog/2022/01/15/destructive-malware-targeting-ukrainian-organizations/
    - https://www.microsoft.com/en-us/security/blog/2023/05/24/volt-typhoon-targets-us-critical-infrastructure-with-living-off-the-land-techniques/
analytic_story:
    - SolarWinds WHD RCE Post Exploitation
    - CISA AA22-320A
    - Hermetic Wiper
    - Sandworm Tools
    - Qakbot
    - Volt Typhoon
    - NOBELIUM Group
    - Data Destruction
    - Lumma Stealer
    - Malicious PowerShell
    - DarkCrystal RAT
    - WhisperGate
    - Crypto Stealer
    - Microsoft SharePoint Vulnerabilities
    - Scattered Spider
    - GhostRedirector IIS Module and Rungan Backdoor
    - Microsoft WSUS CVE-2025-59287
asset_type: Endpoint
mitre_attack_id:
    - T1027
product:
    - Splunk Enterprise
    - Splunk Enterprise Security
    - Splunk Cloud
category: endpoint
security_domain: endpoint
tests:
    - name: True Positive Test
      attack_data:
        - data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1027/atomic_red_team/windows-sysmon.log
          source: XmlWinEventLog:Microsoft-Windows-Sysmon/Operational
          sourcetype: XmlWinEventLog
      test_type: unit

[[ currentRule.title && currentRule.title.length > 60 ? currentRule.title.slice(0, 60) + '…' : currentRule.title ]]

e0d9eef6-6986-426f-86c9-a8f6b24253d1

Propose edits, view related rules, and engage with the community through comments.

Executable code, not a declarative rule

This submission is arbitrary [[ currentRule.format ? currentRule.format.toUpperCase() : '' ]] code, not a declarative detection rule — review it as you would any script before running it, and note that it cannot be safely aggregated or auto-executed alongside YARA/Sigma/Suricata/CRS rules.

Rejected pattern present

[[ reason ]]

What does this mean?

Format & documentation suggestions

Not a security issue — this rule is valid and was accepted as-is. These are optional fields/conventions its own format recommends, mainly affecting its quality score and how well it documents itself for other reviewers.

[[ reason ]]

What do these messages mean?

[[ currentRule.title && currentRule.title.length > 60 ? currentRule.title.slice(0, 60) + '…' : currentRule.title ]]

[[ currentRule.title ]]

Community Discussion