Win32FertgerHavex

Hunt Hypothesis

This hunt hypothesis targets adversaries executing Havex malware variants that leverage specific file integrity patterns to establish persistence and command-and-control channels within Windows environments. Proactive hunting for this behavior in Azure Sentinel is critical because early detection of these low-severity indicators can reveal stealthy lateral movement before the malware escalates to a high-impact incident.

YARA Rule

rule Win32FertgerHavex
{
    meta:
        Author      = "BAE Systems"
        Date        = "2014/06/23"
        Description = "Rule for identifying Fertger version of HAVEX"
        Reference   = "www.f-secure.com/weblog/archives/00002718.html"

    strings:
        $mz = "MZ"
        $a1="\\\\.\\pipe\\mypipe-f" wide
        $a2="\\\\.\\pipe\\mypipe-h" wide
        $a3="\\qln.dbx" wide
        $a4="*.yls" wide
        $a5="\\*.xmd" wide
        $a6="fertger" wide
        $a7="havex"
    
    condition:
        $mz at 0 and 3 of ($a*) 
}

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 8 string patterns in its detection logic.

• Source Rule

False Positive Guidance

Here are 5 specific false positive scenarios for the Win32FertgerHavex detection rule in an enterprise environment, including suggested filters and exclusions:

• Endpoint Protection Engine Updates

  • Scenario: The deployment of signature updates or engine upgrades by major EDR solutions (e.g., CrowdStrike Falcon, Microsoft Defender for Endpoint, or SentinelOne) often involves the extraction of compressed archives containing executable payloads. These processes may temporarily spawn child processes with memory signatures resembling Havex’s file manipulation behaviors, particularly when updating the C:\ProgramData directory.
  • Suggested Filter: Exclude process trees where the parent is a known security vendor service (e.g., CrowdStrike.exe, MsMpEng.exe) and the file path contains standard update directories like \Updates\ or \Temp\.

• Enterprise Patch Management Deployments

  • Scenario: Scheduled patching jobs executed by tools such as Microsoft SCCM (Configuration Manager), Ivanti, or ManageEngine Endpoint Central. During a “push” event, these agents download and unpack software packages. The unpacking of .msi or .cab files often triggers the same file creation and registry modification patterns that the Havex YARA rule monitors for initial infection vectors.
  • Suggested Filter: Create an exclusion based on the CommandLine argument containing specific deployment identifiers (e.g., --deployment-id, /packageid) and restrict the scope to known administrative accounts running during maintenance windows (e.g., 02:00–04:00 UTC).

• Automated Backup and Archiving Tasks

  • Scenario: Scheduled backup jobs using enterprise tools like Veeam Agent, Commvault, or Acronis Cyber Protect. These applications frequently compress large datasets into archives (`.zip