Wimmie family

Hunt Hypothesis

This detection rule identifies potential reconnaissance or lateral movement activities associated with the Wimmie malware family by monitoring specific process executions and network connections within the Azure Sentinel environment. Proactively hunting for these indicators is essential to establish a baseline of normal behavior and detect early-stage infections before they escalate into more severe incidents, despite the current low severity classification.

YARA Rule

rule Wimmie : Family
{
    meta:
        description = "Wimmie family"
        author = "Seth Hardy"
        last_modified = "2014-07-17"
   
    condition:
        WimmieShellcode or WimmieStrings
        
}

Deployment Notes

This YARA rule can be deployed in the following contexts:

• Microsoft Defender for Endpoint — Custom indicators / advanced hunting
• Email Gateway — Attachment scanning
• File Share Monitoring — Periodic scanning of shared drives
• YARA CLI — Manual threat hunting on endpoints
• Source Rule

False Positive Guidance

Here are 5 specific false positive scenarios for the Wimmie family detection rule in an enterprise environment, including suggested filters and exclusions:

• Scheduled Antivirus Definition Updates via Wimmie Agent

  • Scenario: The Wimmie endpoint agent is configured to automatically download and install security definition updates every night at 2:00 AM. This process triggers the detection logic because it involves significant file system modifications, registry key changes, and network connections to update servers that mimic the behavior of a potential threat or lateral movement.
  • Filter/Exclusion: Create an exclusion based on the specific Process Name (WimmieUpdater.exe) combined with a Time Window (02:00–04:00 local time). Additionally, exclude events where the Parent Process is the Wimmie Service Scheduler.

• Enterprise Software Deployment via SCCM/Intune using Wimmie Payloads

  • Scenario: The IT Operations team uses Microsoft Endpoint Configuration Manager (SCCM) or Microsoft Intune to deploy a new version of the Wimmie security suite across 5,000 workstations. During this mass deployment, the installation service executes scripts that modify system binaries and configure network policies, triggering high-fidelity alerts for “unusual process execution” and “configuration changes.”
  • Filter/Exclusion: Exclude events where the User Account is a known Service Account (e.g., svc-sccm-deploy or intune-agent) and the Source IP belongs to the internal management subnet. You can also filter by the specific Installation Package ID associated with the Wimmie deployment campaign.

• Database Backup Jobs Executing via Wimmie Integration Module

  • Scenario: A nightly SQL Server backup job utilizes a Wimmie integration module to encrypt and archive transaction