Windows file write events where executables save files with suspicious script/binary extensions

Alerts when common Windows system executables write files ending in suspicious extensions like .ps1, .bat, .vbs, or .hta.

FreeReviewedSigma · High · v2

Product: windows
Category: file_event
Author: Nasreddine Bencherchali (Nextron Systems) (SigmaHQ), DRL 1.1
Published: 2022-08-12
Updated: 2026-07-31

Analysis Detection

ATT&CK techniques

Defense Evasion

Recon
Resource Dev
Initial Access
Execution
Persistence
Priv Esc
Defense Evasion
- T1036Masquerading
Cred Access
Discovery
Lateral Movement
Collection
C2
Exfiltration
Impact

What it detects

This rule flags Windows processes associated with common system executables that write files whose names end with potentially suspicious extensions such as .bat, .hta, .ps1, .vbs, .dll, .exe, .iso, and .txt. Attackers often stage or deploy malicious payloads by dropping scripts, installers, or signed/packaged content to disk under these extensions. It relies on Windows file event telemetry capturing the writing process image path and the target filename extension, while excluding specific known test/GPO/packaging paths to reduce noise.

Reporting behind it

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Windows file write events where executables save files with suspicious script/binary extensions

Pivot detection · T1036 · 9 related

Changelog

v2
Candidate ingested via manual entry.2026-07-31
v1
No changelog recorded for this version.2026-07-30

Detection content is published as a reviewed draft. Tune thresholds and exclusions against your own telemetry before enabling this rule for alerting.

windows-file-events-executables-writing-files-with-suspicious-extensions-b8fd0e93

title: Windows file write events where executables save files with suspicious script/binary extensions
id: e5dac084-2ce0-415a-96f1-81bccf8d7fb6
related:
  - id: 1277f594-a7d1-4f28-a2d3-73af5cbeab43
    type: derived
  - id: b8fd0e93-ff58-4cbd-8f48-1c114e342e62
    type: derived
status: test
description: This rule flags Windows processes associated with common system executables that write files whose names end with potentially suspicious extensions such as .bat, .hta, .ps1, .vbs, .dll, .exe, .iso, and .txt. Attackers often stage or deploy malicious payloads by dropping scripts, installers, or signed/packaged content to disk under these extensions. It relies on Windows file event telemetry capturing the writing process image path and the target filename extension, while excluding specific known test/GPO/packaging paths to reduce noise.
references:
  - Internal Research
  - https://github.com/SigmaHQ/sigma/blob/master/rules/windows/file/file_event/file_event_win_shell_write_susp_files_extensions.yml
author: Nasreddine Bencherchali (Nextron Systems), Huntrule Team
date: 2022-08-12
modified: 2025-10-07
tags:
  - attack.stealth
  - attack.t1036
logsource:
  category: file_event
  product: windows
detection:
  selection_generic:
    Image|endswith:
      - \csrss.exe
      - \lsass.exe
      - \RuntimeBroker.exe
      - \sihost.exe
      - \smss.exe
      - \wininit.exe
      - \winlogon.exe
    TargetFilename|endswith:
      - .bat
      - .dll
      - .exe
      - .hta
      - .iso
      - .ps1
      - .txt
      - .vbe
      - .vbs
  selection_special:
    Image|endswith:
      - \dllhost.exe
      - \rundll32.exe
      - \svchost.exe
    TargetFilename|endswith:
      - .bat
      - .hta
      - .iso
      - .ps1
      - .vbe
      - .vbs
  filter_main_AppLockerPolicyTest:
    Image: C:\Windows\System32\dllhost.exe
    TargetFilename|contains|all:
      - :\Users\
      - \AppData\Local\Temp\__PSScriptPolicyTest_
    TargetFilename|endswith: .ps1
  filter_main_script_gpo_machine:
    Image: C:\Windows\system32\svchost.exe
    TargetFilename|contains|all:
      - C:\Windows\System32\GroupPolicy\DataStore\
      - \sysvol\
      - \Policies\
      - \Machine\Scripts\Startup\
    TargetFilename|endswith:
      - .ps1
      - .bat
  filter_main_clipchamp:
    Image: C:\Windows\system32\svchost.exe
    TargetFilename|contains|all:
      - C:\Program Files\WindowsApps\Clipchamp
      - .ps1
  filter_main_powershell_preview:
    Image:
      - C:\Windows\system32\svchost.exe
      - C:\Windows\SysWOW64\svchost.exe
    TargetFilename|startswith:
      - C:\Program Files\WindowsApps\Microsoft.PowerShellPreview
      - C:\Program Files (x86)\WindowsApps\Microsoft.PowerShellPreview
    TargetFilename|endswith: .ps1
  condition: 1 of selection_* and not 1 of filter_main_*
falsepositives:
  - Unknown
level: high
license: DRL-1.1

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