Win32OPCHavex

Hunt Hypothesis

This detection identifies the execution of Havex malware within Windows environments by leveraging a specific YARA signature to capture its unique behavioral artifacts. Proactive hunting for this threat in Azure Sentinel is essential to uncover early-stage lateral movement and command-and-control communications that may precede more severe ransomware or botnet activities.

YARA Rule

rule Win32OPCHavex
{
    meta:
        Author      = "BAE Systems"
        Date        = "2014/06/23"
        Description = "Rule for identifying OPC version of HAVEX"
        Reference   = "www.f-secure.com/weblog/archives/00002718.html"

    strings:
        $mzhdr = "MZ"
        $dll = "7CFC52CD3F87.dll"
        $a1 = "Start finging of LAN hosts..." wide
        $a2 = "Finding was fault. Unexpective error" wide
        $a3 = "Was found %i hosts in LAN:" wide
        $a4 = "Hosts was't found." wide
        $a5 = "Start finging of OPC Servers..." wide
        $a6 = "Was found %i OPC Servers." wide
        $a7 = "OPC Servers not found. Programm finished" wide
        $a8 = "%s[%s]!!!EXEPTION %i!!!" wide
        $a9 = "Start finging of OPC Tags..." wide

    condition:
        $mzhdr at 0 and ($dll or (any 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 11 string patterns in its detection logic.

• Source Rule

False Positive Guidance

Here are 4 specific false positive scenarios for the Win32OPCHavex detection rule in an enterprise environment, along with suggested filters or exclusions:

• Antivirus Real-Time Scanning Engine Activity

  • Scenario: The YARA rule may match the signature of legitimate antivirus scanning processes (e.g., MsMpEng.exe for Microsoft Defender or ccSvcHst.exe for CrowdStrike) when they are actively updating their heuristic definitions or performing deep file system scans. These engines often spawn child processes that load similar DLLs or execute memory patterns resembling the Havex malware’s command-and-control initialization.
  • Filter/Exclusion: Exclude known AV service executables from the detection scope by adding a whitelist of process names (e.g., MsMpEng.exe, ccSvcHst.exe, SophosAutoUpdate.exe) and their specific file paths within the %ProgramFiles% directories.

• Scheduled Software Deployment via SCCM or Intune

  • Scenario: During off-hours maintenance windows, System Center Configuration Manager (SCCM) or Microsoft Endpoint Configuration Manager may deploy software updates using PowerShell scripts that invoke msiexec.exe or custom installers. These deployment agents often create temporary files and execute network connections to internal repositories that mimic the Havex beacon behavior, particularly if the installer uses a specific compression library flagged by the YARA rule.
  • Filter/Exclusion: Create an exclusion based on the parent process chain; specifically, exclude events where the parent process is ccmexec.exe (SCCM) or IntuneManagementExtension.exe, and filter out file paths located in temporary deployment folders like %ProgramData%\Microsoft\CCMCache.

• Enterprise Patch Management Scans (e.g., WSUS or Qualys)

  • Scenario: Automated vulnerability scanners such as Qualys Cloud Agent (`