Windows Executable Masquerading as Benign File Types

SPLUNK detection rule by Teoderick Contreras, Splunk · Apache-2.0

The following analytic detects the presence of executable files masquerading as benign file types on Windows systems. Adversaries employ this technique to evade defenses and trick users into executing malicious code by renaming executables with extensions commonly associated with documents, images, or other non-executable formats (e.g., .pdf, .jpg, .doc, .png).

name: Windows Executable Masquerading as Benign File Types
id: 0470c8e7-dd8d-420f-8302-073e8a2b66f0
version: 5
creation_date: '2025-11-21'
modification_date: '2026-05-13'
author: Teoderick Contreras, Splunk
status: production
type: Anomaly
description: |
    The following analytic detects the presence of executable files masquerading as benign file types on Windows systems. Adversaries employ this technique to evade defenses and trick users into executing malicious code by renaming executables with extensions commonly associated with documents, images, or other non-executable formats (e.g., .pdf, .jpg, .doc, .png).
data_source:
    - Sysmon EventID 29
search: |
    `sysmon`
    EventCode=29
    NOT `executable_extensions`
    | stats count min(_time) as firstTime max(_time) as lastTime
      by Image file_name file_path process_guid file_hash process_id dest user EventCode
    | `security_content_ctime(firstTime)`
    | `security_content_ctime(lastTime)`
    | `windows_executable_masquerading_as_benign_file_types_filter`
how_to_implement: |
    To implement Sysmon EventCode 29 (File Block Executable), you must ensure that your Sysmon deployment is configured to log instances where executable file creation is blocked based on your organization's FileBlockExecutable rules. Once enabled, the corresponding Splunk search requires Sysmon operational logs and an input macro named sysmon, which should be customized to match your environment-specific index, source, and sourcetype settings for Windows Sysmon data. We strongly recommend replacing this macro with values appropriate to your Splunk environment so the search scopes correctly. The search also uses a post-filter macro designed to filter out known false positives.
known_false_positives: |
    File types that are not included in the filter for this detection may generate false positives, so proper filtering is required.
references:
    - https://www.linkedin.com/posts/mauricefielenbach_cybersecurity-incidentresponse-dfir-activity-7394805779448418304-g0gZ?utm_source=share&utm_medium=member_desktop&rcm=ACoAAAuFTjIB5weY_kcyu4qp3kHbI4v49tO0zEk
    - https://www.blackhillsinfosec.com/a-sysmon-event-id-breakdown/
    - https://thedfirreport.com/2023/10/30/netsupport-intrusion-results-in-domain-compromise/
    - https://www.esentire.com/blog/evalusion-campaign-delivers-amatera-stealer-and-netsupport-rat
drilldown_searches:
    - name: View the detection results for - "$dest$"
      search: '%original_detection_search% | search  dest = "$dest$"'
      earliest_offset: $info_min_time$
      latest_offset: $info_max_time$
    - name: View risk events for the last 7 days for - "$dest$"
      search: '| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$dest$") | 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: dest
          type: system
          score: 20
          message: A valid Windows PE executable $file_name$ located in $file_path$ was dropped on $dest$, disguised as a non-executable file type.
threat_objects:
    - field: Image
      type: process
    - field: file_name
      type: file_name
    - field: file_path
      type: file_path
analytic_story:
    - NetSupport RMM Tool Abuse
asset_type: Endpoint
mitre_attack_id:
    - T1036.008
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/T1036.008/masquerading_executable_as_non_exec_file_type/non_exec_ext_but_exec_detected.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 ]]

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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

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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 ]]

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

[[ currentRule.title ]]

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