Rundll32 Internet Connection — Sigma Rule

Rule metadata and linked tags

Author: Florian Roth (Nextron Systems). Source status: test; severity: medium. Source dates: 2017-11-04 / 2024-03-13.

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

Pinned original Sigma rule · Detection Rule License 1.1

Source SHA-256: eb22c396d43e207c3bcd5e97425d30ba4b31111127bce2e85863a1fb53c3d2d2

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: Rundll32 Internet Connection
id: cdc8da7d-c303-42f8-b08c-b4ab47230263
status: test
description: Detects a rundll32 that communicates with public IP addresses
references:
    - https://www.hybrid-analysis.com/sample/759fb4c0091a78c5ee035715afe3084686a8493f39014aea72dae36869de9ff6?environmentId=100
author: Florian Roth (Nextron Systems)
date: 2017-11-04
modified: 2024-03-13
tags:
    - attack.stealth
    - attack.t1218.011
    - attack.execution
logsource:
    category: network_connection
    product: windows
detection:
    selection:
        Image|endswith: '\rundll32.exe'
        Initiated: 'true'
    filter_main_local_ranges:
        DestinationIp|cidr:
            - '127.0.0.0/8'
            - '10.0.0.0/8'
            - '172.16.0.0/12'
            - '192.168.0.0/16'
            - '169.254.0.0/16'
            - '::1/128'  # IPv6 loopback
            - 'fe80::/10'  # IPv6 link-local addresses
            - 'fc00::/7'  # IPv6 private addresses
    filter_main_ms_ranges:
        DestinationIp|cidr:
            - '20.0.0.0/8' # Microsoft range, caused some FPs
            - '51.103.0.0/16' # Microsoft AS8075 range, caused some FPs
            - '51.104.0.0/16' # Microsoft AS8075 range, caused some FPs
            - '51.105.0.0/16' # Microsoft AS8075 range, caused some FPs
    filter_main_app_sdb:
        CommandLine|endswith: '\system32\PcaSvc.dll,PcaPatchSdbTask'
    filter_main_azure_managed:
        SourceHostname|endswith: '.internal.cloudapp.net'
    filter_main_svchost_update_processes:
        # Note: This require "ParentImage" data enrichment.
        ParentImage: 'C:\Windows\System32\svchost.exe'
        DestinationPort: 443
    condition: selection and not 1 of filter_main_*
falsepositives:
    - Communication to other corporate systems that use IP addresses from public address spaces
level: medium

Original YAML and metadata in JSON

False positives

• Communication to other corporate systems that use IP addresses from public address spaces

Source references

• https://www.hybrid-analysis.com/sample/759fb4c0091a78c5ee035715afe3084686a8493f39014aea72dae36869de9ff6?environmentId=100