Potentially Suspicious Execution Of Regasm/Regsvcs With Uncommon Extension — Sigma Rule

Rule metadata and linked tags

Author: Nasreddine Bencherchali (Nextron Systems). Source status: test; severity: medium. Source dates: 2023-02-13 / not supplied.

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

Pinned original Sigma rule · Detection Rule License 1.1

Source SHA-256: 383e2b5e706c1431f2f1b55b6071cb98abca7b042c910ba34ba6b03a833f99d6

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: Potentially Suspicious Execution Of Regasm/Regsvcs With Uncommon Extension
id: e9f8f8cc-07cc-4e81-b724-f387db9175e4
related:
    - id: cc368ed0-2411-45dc-a222-510ace303cb2
      type: derived
status: test
description: Detects potentially suspicious execution of the Regasm/Regsvcs utilities with an uncommon extension.
references:
    - https://www.fortiguard.com/threat-signal-report/4718?s=09
    - https://lolbas-project.github.io/lolbas/Binaries/Regasm/
    - https://lolbas-project.github.io/lolbas/Binaries/Regsvcs/
author: Nasreddine Bencherchali (Nextron Systems)
date: 2023-02-13
tags:
    - attack.stealth
    - attack.t1218.009
logsource:
    category: process_creation
    product: windows
detection:
    selection_img:
        - Image|endswith:
              - '\Regsvcs.exe'
              - '\Regasm.exe'
        - OriginalFileName:
              - 'RegSvcs.exe'
              - 'RegAsm.exe'
    selection_extension:
        CommandLine|contains:
            # Note: Add more potentially uncommon extensions
            - '.dat'
            - '.gif'
            - '.jpeg'
            - '.jpg'
            - '.png'
            - '.txt'
    condition: all of selection_*
falsepositives:
    - Unknown
level: medium

Original YAML and metadata in JSON

False positives

• Unknown

Source references

• https://www.fortiguard.com/threat-signal-report/4718?s=09
• https://lolbas-project.github.io/lolbas/Binaries/Regasm/
• https://lolbas-project.github.io/lolbas/Binaries/Regsvcs/