Potential Direct Syscall of NtOpenProcess — Sigma Rule

Rule metadata and linked tags

Author: Christian Burkard (Nextron Systems), Tim Shelton (FP). Source status: test; severity: medium. Source dates: 2021-07-28 / 2023-12-13.

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

Pinned original Sigma rule · Detection Rule License 1.1

Source SHA-256: 1b735d42840bb6c1fbcf7bb506675babe9ba14329728131848e6bfe671f05675

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: Potential Direct Syscall of NtOpenProcess
id: 3f3f3506-1895-401b-9cc3-e86b16e630d0
status: test
description: Detects potential calls to NtOpenProcess directly from NTDLL.
references:
    - https://medium.com/falconforce/falconfriday-direct-system-calls-and-cobalt-strike-bofs-0xff14-741fa8e1bdd6
author: Christian Burkard (Nextron Systems), Tim Shelton (FP)
date: 2021-07-28
modified: 2023-12-13
tags:
    - attack.execution
    - attack.t1106
logsource:
    category: process_access
    product: windows
detection:
    selection:
        CallTrace|startswith: 'UNKNOWN'
    filter_main_vcredist:
        TargetImage|endswith: 'vcredist_x64.exe'
        SourceImage|endswith: 'vcredist_x64.exe'
    filter_main_generic:
        # Examples include "systeminfo", "backgroundTaskHost", "AUDIODG"
        SourceImage|contains:
            - ':\Program Files (x86)\'
            - ':\Program Files\'
            - ':\Windows\System32\'
            - ':\Windows\SysWOW64\'
            - ':\Windows\WinSxS\'
        TargetImage|contains:
            - ':\Program Files (x86)\'
            - ':\Program Files\'
            - ':\Windows\System32\'
            - ':\Windows\SysWOW64\'
            - ':\Windows\WinSxS\'
    filter_main_kerneltrace_edge:
        # Cases in which the CallTrace is just e.g. 'UNKNOWN(19290435374)' from Microsoft-Windows-Kernel-Audit-API-Calls provider
        Provider_Name: 'Microsoft-Windows-Kernel-Audit-API-Calls'
    filter_optional_vmware:
        TargetImage|endswith: ':\Windows\system32\systeminfo.exe'
        SourceImage|endswith: 'setup64.exe' # vmware
    filter_optional_cylance:
        SourceImage|endswith: ':\Windows\Explorer.EXE'
        TargetImage|endswith: ':\Program Files\Cylance\Desktop\CylanceUI.exe'
    filter_optional_amazon:
        SourceImage|endswith: 'AmazonSSMAgentSetup.exe'
        TargetImage|endswith: 'AmazonSSMAgentSetup.exe'
    filter_optional_vscode: # VsCode
        SourceImage|endswith: '\AppData\Local\Programs\Microsoft VS Code\Code.exe'
        TargetImage|endswith: '\AppData\Local\Programs\Microsoft VS Code\Code.exe'
    filter_optional_teams: # MS Teams
        TargetImage|endswith: '\AppData\Local\Microsoft\Teams\current\Teams.exe'
        SourceImage|endswith: '\AppData\Local\Microsoft\Teams\current\Teams.exe'
    filter_optional_discord: # Discord
        TargetImage|contains: '\AppData\Local\Discord\'
        TargetImage|endswith: '\Discord.exe'
    filter_optional_yammer:
        SourceImage|contains: '\AppData\Local\yammerdesktop\app-'
        SourceImage|endswith: '\Yammer.exe'
        TargetImage|contains: '\AppData\Local\yammerdesktop\app-'
        TargetImage|endswith: '\Yammer.exe'
        GrantedAccess: '0x1000'
    filter_optional_evernote:
        TargetImage|endswith: '\Evernote\Evernote.exe'
    filter_optional_adobe_acrobat:
        SourceImage|contains: ':\Program Files\Adobe\Acrobat DC\Acrobat\'
        SourceImage|endswith: '\AcroCEF.exe'
        TargetImage|contains: ':\Program Files\Adobe\Acrobat DC\Acrobat\'
        TargetImage|endswith: '\AcroCEF.exe'
    condition: selection and not 1 of filter_main_* and not 1 of filter_optional_*
falsepositives:
    - Unknown
level: medium

Original YAML and metadata in JSON

False positives

• Unknown

Source references

• https://medium.com/falconforce/falconfriday-direct-system-calls-and-cobalt-strike-bofs-0xff14-741fa8e1bdd6