Chopper Webshell Process Pattern

Hunt Hypothesis

Detects patterns found in process executions cause by China Chopper like tiny (ASPX) webshells

Detection Rule

Sigma (Original)

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

KQL (Azure Sentinel)

imProcessCreate
| where (TargetProcessName endswith "\\w3wp.exe" or (ParentProcessName endswith "\\w3wp.exe" or ActingProcessName endswith "\\w3wp.exe")) and (TargetProcessCommandLine contains "&ipconfig&echo" or TargetProcessCommandLine contains "&quser&echo" or TargetProcessCommandLine contains "&whoami&echo" or TargetProcessCommandLine contains "&c:&echo" or TargetProcessCommandLine contains "&cd&echo" or TargetProcessCommandLine contains "&dir&echo" or TargetProcessCommandLine contains "&echo [E]" or TargetProcessCommandLine contains "&echo [S]")

Required Data Sources

False Positive Guidance

• Unknown

MITRE ATT&CK Context

• Tactic: Persistence
• Tactic: Discovery
• Technique: T1505.003 — T1505.003
• Technique: T1018 — T1018
• Technique: T1033 — T1033
• Technique: T1087 — T1087

References

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