Stuxnet Sample - file dll.dll

Hunt Hypothesis

The detection of a Stuxnet sample file named dll.dll indicates potential adversary behavior involving advanced persistent threats leveraging legacy malware techniques. SOC teams should proactively hunt for this behavior in Azure Sentinel to identify and mitigate potential long-term compromise and data exfiltration risks.

YARA Rule

rule StuxNet_dll 
{

    meta:
        description = "Stuxnet Sample - file dll.dll"
        author = "Florian Roth"
        reference = "Internal Research"
        date = "2016-07-09"
        hash1 = "9e392277f62206098cf794ddebafd2817483cfd57ec03c2e05e7c3c81e72f562"

    strings:
        $s1 = "SUCKM3 FROM EXPLORER.EXE MOTH4FUCKA #@!" fullword ascii
    
    condition:
        uint16(0) == 0x5a4d and filesize < 100KB and $s1
}

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.

References

• Internal Research
• Source Rule

False Positive Guidance

• Scenario: Scheduled system update or patch deployment using Windows Update or Microsoft Endpoint Manager (MEM)
  Filter/Exclusion: Check for ProcessName containing wuauclt.exe or MsMpEng.exe, or filter by ParentProcessName matching known update services.

• Scenario: Legitimate use of DLL files in a development or testing environment (e.g., Visual Studio or PowerShell scripts)
  Filter/Exclusion: Filter by ProcessName containing devenv.exe, powershell.exe, or msbuild.exe, or check for User matching development team accounts.

• Scenario: System file integrity check using Sysinternals tools like Process Explorer or Autoruns
  Filter/Exclusion: Filter by ProcessName containing procexp.exe or autoruns.exe, or check for CommandLine containing –enable or –disable.

• Scenario: Administrative task involving DLL file replacement during a software upgrade (e.g., SQL Server or Exchange Server updates)
  Filter/Exclusion: Filter by ProcessName containing setup.exe, msiexec.exe, or sqlservr.exe, or check for ParentProcessName matching known installation tools.

• Scenario: Third-party application using a DLL file for legitimate functionality (e.g., Adobe Acrobat or VMware Tools)
  Filter/Exclusion: Filter by ProcessName containing AcroRd32.exe, vmtoolsd.exe, or vboxtray.exe, or check for FileHash matching known vendor-signed DLLs.