Chopper Webshell Process Pattern — Sigma Rule

Rule metadata and linked tags

Author: Florian Roth (Nextron Systems), MSTI (query). Source status: test; severity: high. Source dates: 2022-10-01 / not supplied.

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

Pinned original Sigma rule · Detection Rule License 1.1

Source SHA-256: bd83b28a410589b85ce907907a56adb48b973b2f6372a27c24c1be58464afc19

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: Chopper Webshell Process Pattern
id: fa3c117a-bc0d-416e-a31b-0c0e80653efb
status: test
description: Detects patterns found in process executions cause by China Chopper like tiny (ASPX) webshells
references:
    - https://www.microsoft.com/security/blog/2022/09/30/analyzing-attacks-using-the-exchange-vulnerabilities-cve-2022-41040-and-cve-2022-41082/
author: Florian Roth (Nextron Systems), MSTI (query)
date: 2022-10-01
tags:
    - attack.persistence
    - attack.discovery
    - attack.t1505.003
    - attack.t1018
    - attack.t1033
    - attack.t1087
logsource:
    category: process_creation
    product: windows
detection:
    selection_origin:
        - Image|endswith: '\w3wp.exe'
        - ParentImage|endswith: '\w3wp.exe'
    selection_cmdline:
        CommandLine|contains:
            - '&ipconfig&echo'
            - '&quser&echo'
            - '&whoami&echo'
            - '&c:&echo'
            - '&cd&echo'
            - '&dir&echo'
            - '&echo [E]'
            - '&echo [S]'
    condition: all of selection_*
falsepositives:
    - Unknown
level: high

Original YAML and metadata in JSON

False positives

• Unknown

Source references

• https://www.microsoft.com/security/blog/2022/09/30/analyzing-attacks-using-the-exchange-vulnerabilities-cve-2022-41040-and-cve-2022-41082/