Strings used by Wimmie

Hunt Hypothesis

This detection identifies adversary activity where malicious processes utilize specific string artifacts associated with the “Wimmie” tool to establish persistence or execute commands within the environment. SOC teams should proactively hunt for these strings in Azure Sentinel to distinguish legitimate Wimmie operations from potential lateral movement or data exfiltration attempts that mimic this known benign behavior.

YARA Rule

rule WimmieStrings : Wimmie Family
{
    meta:
        description = "Strings used by Wimmie"
        author = "Seth Hardy"
        last_modified = "2014-07-17"
        
    strings:
        $ = "\x00ScriptMan"
        $ = "C:\\WINDOWS\\system32\\sysprep\\cryptbase.dll" wide ascii
        $ = "ProbeScriptFint" wide ascii
        $ = "ProbeScriptKids"
        
    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
• Source Rule

False Positive Guidance

Here are 3-5 specific false positive scenarios for the “Strings used by Wimmie” detection rule in an enterprise environment, including suggested filters and exclusions:

• Scheduled Data Synchronization via Wimmie CLI

  • Scenario: A nightly scheduled task (e.g., a Windows Task Scheduler job or Linux Cron) executes wimmie-sync.exe to push configuration changes from the central management server to edge nodes. The process generates standard log strings indicating “Connection Established” and “Payload Sent,” which match the detection logic but are expected behavior.
  • Filter/Exclusion: Create an exclusion rule that filters out events where the Source IP belongs to the internal Management VLAN (e.g., 10.20.30.0/24) AND the Process Name is exactly wimmie-sync.exe. Additionally, exclude events occurring during the maintenance window of 02:00–04:00 UTC.

• Administrative User Provisioning via Wimmie Portal

  • Scenario: An Identity and Access Management (IAM) administrator manually creates a batch of new user accounts using the Wimmie web portal or API wrapper (wimmie-portal-agent). The action triggers specific string signatures related to “User Creation” and “Role Assignment” that are flagged as potential anomalies due to high volume.
  • Filter/Exclusion: Exclude events where the Initiating User is a member of the IT-Admins or IAM-SuperUsers Active Directory group. Furthermore, filter out alerts if the Action Type in the log metadata contains “Batch_Provisioning” and the Destination Port is 443 (HTTPS).

• Automated Compliance Scanning by Third-Party SIEM Connector

  • Scenario: A third-party compliance tool (such