Suspicious Child Process of AspNetCompiler — Sigma Rule

Rule metadata and linked tags

Author: Nasreddine Bencherchali (Nextron Systems). Source status: test; severity: high. Source dates: 2023-08-14 / not supplied.

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

Pinned original Sigma rule · Detection Rule License 1.1

Source SHA-256: bdc0ed035f5aa4029462b87daff9d1db4ae84fdcada5254b7408d56d7d20a7ae

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: Suspicious Child Process of AspNetCompiler
id: 9ccba514-7cb6-4c5c-b377-700758f2f120 # SuspChild
related:
    - id: 4c7f49ee-2638-43bb-b85b-ce676c30b260 # TMP File
      type: similar
    - id: 9f50fe98-fe5c-4a2d-86c7-fad7f63ed622 # Susp Paths
      type: similar
    - id: a01b8329-5953-4f73-ae2d-aa01e1f35f00 # Exec
      type: similar
status: test
description: Detects potentially suspicious child processes of "aspnet_compiler.exe".
references:
    - https://lolbas-project.github.io/lolbas/Binaries/Aspnet_Compiler/
    - https://ijustwannared.team/2020/08/01/the-curious-case-of-aspnet_compiler-exe/
author: Nasreddine Bencherchali (Nextron Systems)
date: 2023-08-14
tags:
    - attack.execution
    - attack.stealth
    - attack.t1127
logsource:
    category: process_creation
    product: windows
detection:
    selection_parent:
        ParentImage|endswith: '\aspnet_compiler.exe'
    selection_child:
        # Note: add other potential suspicious child processes and paths
        - Image|endswith:
              - '\calc.exe'
              - '\notepad.exe'
        - Image|contains:
              - '\Users\Public\'
              - '\AppData\Local\Temp\'
              - '\AppData\Local\Roaming\'
              - ':\Temp\'
              - ':\Windows\Temp\'
              - ':\Windows\System32\Tasks\'
              - ':\Windows\Tasks\'
    condition: all of selection_*
falsepositives:
    - Unknown
level: high

Original YAML and metadata in JSON

False positives

• Unknown

Source references

• https://lolbas-project.github.io/lolbas/Binaries/Aspnet_Compiler/
• https://ijustwannared.team/2020/08/01/the-curious-case-of-aspnet_compiler-exe/