Detects a Winnti malware - Streamportal

Hunt Hypothesis

The hypothesis is that the detection of the Winnti malware family via the Streamportal campaign indicates potential adversary activity involving data exfiltration and lateral movement within a network. SOC teams should proactively hunt for this behavior in Azure Sentinel to identify and mitigate advanced persistent threats before significant data loss or network compromise occurs.

YARA Rule

rule Winnti_malware_StreamPortal_Gen 
{

    meta:
        description = "Detects a Winnti malware - Streamportal"
        author = "Florian Roth"
        reference = "VTI research"
        date = "2015-10-10"
        score = 75
        hash1 = "326e2cabddb641777d489a9e7a39d52c0dc2dcb1fde1762554ea162792056b6e"
        hash2 = "9001572983d5b1f99787291edaadbb65eb2701722f52470e89db2c59def24672"
        hash3 = "aff7c7478fe33c57954b6fec2095efe8f9edf5cdb48a680de9439ba62a77945f"
  
    strings:
        $s0 = "Proxies destination address/port for TCP" fullword wide
        $s3 = "\\Device\\StreamPortal" fullword wide
        $s4 = "Transport-Data Proxy Sub-Layer" fullword wide
        $s5 = "Cookie: SN=" fullword ascii
        $s6 = "\\BaseNamedObjects\\_transmition_synchronization_" fullword wide
        $s17 = "NTOSKRNL.EXE" fullword wide /* Goodware String - occured 4 times */
        $s19 = "FwpsReferenceNetBufferList0" fullword ascii /* Goodware String - occured 5 times */
  
    condition:
        uint16(0) == 0x5a4d and filesize < 275KB and all 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 7 string patterns in its detection logic.

References

• VTI research
• Source Rule

False Positive Guidance

• Scenario: Scheduled System Maintenance Task
  Description: A legitimate scheduled task runs a script or executable that matches the YARA signature due to similar file structure or naming conventions.
  Filter/Exclusion: Exclude processes associated with schtasks.exe or tasks scheduled via the Task Scheduler with a known benign command line.

• Scenario: Windows Update or Patching Tool Execution
  Description: A tool like wusa.exe (Windows Update Standalone Setup) or msiexec.exe (used for installing patches) may trigger the rule due to similar binary characteristics.
  Filter/Exclusion: Exclude processes with wusa.exe, msiexec.exe, or setup.exe and check for the presence of known Windows update hashes or digital signatures.

• Scenario: Admin Tool or PowerShell Script Execution
  Description: An admin might run a PowerShell script or a legitimate administrative tool (e.g., PsExec, PSTools, or PowerShell.exe) that has a similar file signature to the malware.
  Filter/Exclusion: Exclude processes initiated from the command line with powershell.exe or psexec.exe and check for the presence of a valid digital certificate or known admin tool hash.

• Scenario: Antivirus or Endpoint Protection Scan
  Description: A legitimate antivirus tool (e.g., avgscan.exe, mcafee.exe, or bitdefender.exe) may be flagged due to overlapping YARA rule patterns.
  Filter/Exclusion: Exclude processes associated with known antivirus vendors and check for the presence of a valid vendor signature or process name.

• Scenario: Logon Script or Group Policy Execution
  Description: A logon script or Group Policy Object (GPO) may execute a script or executable that matches the YARA signature due to similar code patterns.
  *Filter