Change Default File Association To Executable Via Assoc — Sigma Rule

Rule metadata and linked tags

Author: Nasreddine Bencherchali (Nextron Systems). Source status: test; severity: high. Source dates: 2022-06-28 / 2023-03-06.

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

Pinned original Sigma rule · Detection Rule License 1.1

Source SHA-256: d98d35d6a6ac3561849b9c5aa7acb5ffad0ab5af9ad515479c86c6f3c9de2083

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: Change Default File Association To Executable Via Assoc
id: ae6f14e6-14de-45b0-9f44-c0986f50dc89
related:
    - id: 3d3aa6cd-6272-44d6-8afc-7e88dfef7061
      type: derived
status: test
description: |
    Detects when a program changes the default file association of any extension to an executable.
    When a file is opened, the default program used to open the file (also called the file association or handler) is checked. File association selections are stored in the Windows Registry and can be edited by users, administrators, or programs that have Registry access or by administrators using the built-in assoc utility. Applications can modify the file association for a given file extension to call an arbitrary program when a file with the given extension is opened.
references:
    - https://learn.microsoft.com/en-us/windows-server/administration/windows-commands/assoc
author: Nasreddine Bencherchali (Nextron Systems)
date: 2022-06-28
modified: 2023-03-06
tags:
    - attack.privilege-escalation
    - attack.persistence
    - attack.t1546.001
logsource:
    category: process_creation
    product: windows
detection:
    selection_img:
        - Image|endswith: '\cmd.exe'
        - OriginalFileName: 'Cmd.Exe'
    selection_cli:
        CommandLine|contains|all:
            - 'assoc '
            - 'exefile'
    filter:
        CommandLine|contains: '.exe=exefile'
    condition: all of selection_* and not filter
falsepositives:
    - Unknown
level: high

Original YAML and metadata in JSON

False positives

• Unknown

Source references

• https://learn.microsoft.com/en-us/windows-server/administration/windows-commands/assoc