Detects Emdivi Malware

Hunt Hypothesis

Emdivi malware is likely present in the environment due to the detection of its unique behavioral patterns associated with persistence and lateral movement. SOC teams should proactively hunt for this behavior in Azure Sentinel to identify and contain Emdivi infections before they cause widespread damage.

YARA Rule

rule Emdivi_Gen3 
{

    meta:
        description = "Detects Emdivi Malware"
        author = "Florian Roth @Cyber0ps"
        reference = "https://securelist.com/blog/research/71876/new-activity-of-the-blue-termite-apt/"
        date = "2015-08-20"
        super_rule = 1
        score = 80
        hash1 = "008f4f14cf64dc9d323b6cb5942da4a99979c4c7d750ec1228d8c8285883771e"
        hash2 = "a94bf485cebeda8e4b74bbe2c0a0567903a13c36b9bf60fab484a9b55207fe0d"
  
    strings:
        $x1 = "Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; SV1; .NET CLR 2.0.50727.42)" fullword ascii
        $s2 = "\\Mozilla\\Firefox\\Profiles\\" fullword ascii
        $s4 = "\\auto.cfg" fullword ascii
        $s5 = "/ncsi.txt" fullword ascii
        $s6 = "/en-us/default.aspx" fullword ascii
        $s7 = "cmd /c" fullword ascii
        $s9 = "APPDATA" fullword ascii /* Goodware String - occured 25 times */
   
    condition:
        uint16(0) == 0x5a4d and filesize < 850KB and (( $x1 and 1 of ($s*)) or ( 4 of ($s*)))
}

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

• https://securelist.com/blog/research/71876/new-activity-of-the-blue-termite-apt/
• Source Rule

False Positive Guidance

• Scenario: Scheduled System Maintenance Task
  Description: A legitimate scheduled task runs a script that uses curl or wget to download a file from an internal server.
  Filter/Exclusion: Exclude processes initiated by schtasks.exe or tasks with a known name (e.g., SystemMaintenanceTask).

• Scenario: Software Update via Proxy
  Description: A system updates software using a proxy server, which triggers network traffic similar to Emdivi’s C2 communication.
  Filter/Exclusion: Exclude traffic originating from known update servers (e.g., update.microsoft.com, download.microsoft.com) or processes initiated by wuauclt.exe.

• Scenario: Admin-Initiated File Transfer
  Description: An administrator uses scp or rsync to transfer files between servers, which may resemble Emdivi’s file exfiltration behavior.
  Filter/Exclusion: Exclude processes initiated by ssh or rsync with known admin credentials or from trusted IP ranges.

• Scenario: PowerShell Script for Configuration Management
  Description: A PowerShell script (e.g., from Pester or PSConfig) uses Invoke-WebRequest to fetch a configuration file from a local repository.
  Filter/Exclusion: Exclude processes with the PowerShell executable and script paths in known configuration directories (e.g., C:\Tools\Scripts).

• Scenario: Log Collection via SIEM Agent
  Description: A SIEM agent (e.g., Splunk Universal Forwarder) sends logs to a central server, which may be mistaken for Emdivi’s C2 traffic.
  Filter/Exclusion: Exclude traffic from known SIEM agents (e.g., splunkforwarder.exe) or from the SIEM server IP address.