Windows Binaries Write Suspicious Extensions — Sigma Rule

Rule metadata and linked tags

Author: Nasreddine Bencherchali (Nextron Systems). Source status: test; severity: high. Source dates: 2022-08-12 / 2025-10-07.

{
  "category": "file_event",
  "product": "windows"
}

Pinned original Sigma rule · Detection Rule License 1.1

Source SHA-256: e76229c800add301cb3b1ef3a70276ad42c8980c2cbdc1d36e6bebc22dbfcf40

Detection logic

Original source YAML. Source-tag agreement is not proof of complete semantic coverage. This rule has not been compiled for a SIEM backend or validated against live telemetry here.

title: Windows Binaries Write Suspicious Extensions
id: b8fd0e93-ff58-4cbd-8f48-1c114e342e62
related:
    - id: 1277f594-a7d1-4f28-a2d3-73af5cbeab43
      type: derived
status: test
description: Detects Windows executables that write files with suspicious extensions
references:
    - Internal Research
author: Nasreddine Bencherchali (Nextron Systems)
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

Original YAML and metadata in JSON

False positives

• Unknown

Source references

• Internal Research (source note; no public URL supplied)