Windows File Download Via PowerShell

SPLUNK detection rule by Michael Haag, Nasreddine Bencherchali, Splunk · Apache-2.0

The following analytic detects the use of PowerShell's download methods such as "DownloadString" and "DownloadData" from the WebClient class or Invoke-WebRequest and it's aliases "IWR" or "Curl". It leverages data from Endpoint Detection and Response (EDR) agents, focusing on process execution logs that include command-line details. This activity can be significant such methods and functions are commonly used in malicious PowerShell scripts to fetch and execute remote code. If confirmed malicious, this behavior could allow an attacker to download and run arbitrary code, potentially leading to unauthorized access, data exfiltration, or further compromise of the affected system.

name: Windows File Download Via PowerShell
id: 58c4e56c-b5b8-46a3-b5fb-6537dca3c6de
version: 10
creation_date: '2021-03-01'
modification_date: '2026-07-14'
author: Michael Haag, Nasreddine Bencherchali, Splunk
status: production
type: Anomaly
description: |
    The following analytic detects the use of PowerShell's download methods such as
    "DownloadString" and "DownloadData" from the WebClient class or Invoke-WebRequest
    and it's aliases "IWR" or "Curl".
    It leverages data from Endpoint Detection and Response (EDR) agents, focusing on
    process execution logs that include command-line details.
    This activity can be significant such methods and functions are commonly used in malicious
    PowerShell scripts to fetch and execute remote code.
    If confirmed malicious, this behavior could allow an attacker to download and run
    arbitrary code, potentially leading to unauthorized access, data exfiltration,
    or further compromise of the affected system.
data_source:
    - Sysmon EventID 1
    - Windows Event Log Security 4688
    - CrowdStrike ProcessRollup2
    - Cisco Network Visibility Module Flow Data
search: '| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime from datamodel=Endpoint.Processes where `process_powershell` Processes.process IN ( "*iwr *", "*Invoke-WebRequest*", "*wget *", "curl", "*.DownloadData*", "*.DownloadFile*", "*.DownloadString*" ) 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)` | `windows_file_download_via_powershell_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 may be present and filtering will need to occur
    by parent process or command line argument. It may be required to modify this query
    to an EDR product for more granular coverage.
references:
    - https://learn.microsoft.com/en-us/dotnet/api/system.net.webclient?view=net-9.0#methods
    - https://blog.malwarebytes.com/malwarebytes-news/2021/02/lazyscripter-from-empire-to-double-rat/
    - https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1059.001/T1059.001.md
    - https://thedfirreport.com/2023/05/22/icedid-macro-ends-in-nokoyawa-ransomware/
drilldown_searches:
    - name: View the detection results for - "$user$" and "$dest$"
      search: '%original_detection_search% | search  user = "$user$" dest = "$dest$"'
      earliest_offset: $info_min_time$
      latest_offset: $info_max_time$
    - name: View risk events for the last 7 days for - "$user$" and "$dest$"
      search: '| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$user$", "$dest$") | stats count min(_time) as firstTime max(_time) as lastTime values(search_name) as "Search Name" values(risk_message) as "Risk Message" values(analyticstories) as "Analytic Stories" values(annotations._all) as "Annotations" values(annotations.mitre_attack.mitre_tactic) as "ATT&CK Tactics" by normalized_risk_object | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)`'
      earliest_offset: 7d
      latest_offset: "0"
intermediate_findings:
    entities:
        - field: user
          type: user
          score: 20
          message: File download activity initiated on $dest$ by user $user$. $process_name$ was identified calling a download function $process$
        - field: dest
          type: system
          score: 20
          message: File download activity initiated on $dest$ by user $user$. $process_name$ was identified calling a download function $process$
threat_objects:
    - field: parent_process_name
      type: parent_process_name
    - field: process_name
      type: process_name
analytic_story:
    - APT37 Rustonotto and FadeStealer
    - Cisco Network Visibility Module Analytics
    - Data Destruction
    - GhostRedirector IIS Module and Rungan Backdoor
    - HAFNIUM Group
    - Hermetic Wiper
    - IcedID
    - Ingress Tool Transfer
    - Malicious PowerShell
    - Microsoft WSUS CVE-2025-59287
    - NetSupport RMM Tool Abuse
    - NPM Supply Chain Compromise
    - Phemedrone Stealer
    - PHP-CGI RCE Attack on Japanese Organizations
    - SysAid On-Prem Software CVE-2023-47246 Vulnerability
    - Winter Vivern
    - XWorm
    - Tuoni
    - StealC Stealer
    - SolarWinds WHD RCE Post Exploitation
asset_type: Endpoint
mitre_attack_id:
    - T1059.001
    - T1105
product:
    - Splunk Enterprise
    - Splunk Enterprise Security
    - Splunk Cloud
category: endpoint
security_domain: endpoint
tests:
    - name: True Positive Test - Sysmon
      attack_data:
        - data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1059.001/atomic_red_team/windows-sysmon.log
          source: XmlWinEventLog:Microsoft-Windows-Sysmon/Operational
          sourcetype: XmlWinEventLog
      test_type: unit
    - name: True Positive Test - Cisco NVM
      attack_data:
        - data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/cisco_network_visibility_module/cisco_nvm_flowdata/nvm_flowdata.log
          source: not_applicable
          sourcetype: cisco:nvm:flowdata:v2
      test_type: unit

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

fc2e01bc-c5f8-4804-8f4c-17f3795cf877

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