Wimmie code features

Hunt Hypothesis

This detection rule identifies anomalous execution patterns associated with “Wimmie” code features, which may indicate an adversary attempting to establish a foothold or execute custom scripts within the environment. Proactively hunting for these specific behaviors in Azure Sentinel is essential to validate their legitimacy and prevent potential low-severity indicators from evolving into undetected lateral movement or data exfiltration activities.

YARA Rule

rule WimmieShellcode : Wimmie Family 
{
    meta:
        description = "Wimmie code features"
        author = "Seth Hardy"
        last_modified = "2014-07-17"
        
    strings:
        // decryption loop
        $ = { 49 30 24 39 83 F9 00 77 F7 8D 3D 4D 10 40 00 B9 0C 03 00 00 }
        $xordecrypt = {B9 B4 1D 00 00 [8] 49 30 24 39 83 F9 00 }
        
    condition:
        any of them
}

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

This rule contains 1 string patterns in its detection logic.

• Source Rule

False Positive Guidance

Here are 4 specific false positive scenarios for the “Wimmie code features” detection rule in an enterprise environment, including suggested filters and exclusions:

• Scheduled Backup of Source Control Repositories

  • Scenario: The nightly automated backup job (e.g., using Veeam or AWS Backup) scans the repository containing Wimmie source code artifacts. During this scan, the backup agent reads the specific feature files and metadata associated with “Wimmie code features,” triggering the detection logic as if a new feature was being deployed or modified by a user.
  • Filter/Exclusion: Create an exclusion rule that ignores alerts originating from the service account used by the backup solution (e.g., svc-veeam-backup or aws-backup-agent) during the defined maintenance window (e.g., 02:00 – 04:00 UTC).

• CI/CD Pipeline Artifact Generation

  • Scenario: A continuous integration pipeline (running on Jenkins, GitLab CI, or Azure DevOps) executes a build stage that compiles and packages the Wimmie application. The build agent writes temporary feature configuration files to the staging directory, which mimics the signature of active code feature development, causing the rule to fire for every successful build run rather than just production deployments.
  • Filter/Exclusion: Filter out events where the source IP belongs to the CI/CD runner subnet and the process name matches known pipeline agents (e.g., jenkins-agent, gitlab-runner). Additionally, exclude file paths located in temporary staging directories (e.g., /tmp/build_staging/* or C:\Builds\Temp\*).

• Enterprise Antivirus Deep Scan

  • Scenario: The endpoint protection suite (CrowdStrike, SentinelOne, or **Microsoft