Detects KillDisk malware from BlackEnergy

Hunt Hypothesis

KillDisk malware from BlackEnergy is designed to persistently delete critical system files and disrupt operations, making it a high-impact threat that requires immediate containment. SOC teams should proactively hunt for this behavior in Azure Sentinel to identify and neutralize advanced persistent threats before they cause irreversible damage.

YARA Rule

rule BlackEnergy_KillDisk_2 
{

    meta:
        description = "Detects KillDisk malware from BlackEnergy"
        author = "Florian Roth"
        reference = "http://feedproxy.google.com/~r/eset/blog/~3/BXJbnGSvEFc/"
        date = "2016-01-03"
        score = 80
        super_rule = 1
        hash1 = "11b7b8a7965b52ebb213b023b6772dd2c76c66893fc96a18a9a33c8cf125af80"
        hash2 = "5d2b1abc7c35de73375dd54a4ec5f0b060ca80a1831dac46ad411b4fe4eac4c6"
        hash3 = "f52869474834be5a6b5df7f8f0c46cbc7e9b22fa5cb30bee0f363ec6eb056b95"

    strings:
        $s0 = "%c:\\~tmp%08X.tmp" fullword ascii
        $s1 = "%s%08X.tmp" fullword ascii
        $s2 = ".exe.sys.drv.doc.docx.xls.xlsx.mdb.ppt.pptx.xml.jpg.jpeg.ini.inf.ttf" fullword wide
        $s3 = "%ls_%ls_%ls_%d.~tmp" fullword wide

    condition:
        uint16(0) == 0x5a4d and filesize < 500KB and 3 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 4 string patterns in its detection logic.

References

• http://feedproxy.google.com/~r/eset/blog/~3/BXJbnGSvEFc/
• Source Rule

False Positive Guidance

• Scenario: Scheduled system cleanup using CCleaner
  Filter/Exclusion: process.name != "ccleaner.exe"

• Scenario: Windows Update or Group Policy Update running as part of routine maintenance
  Filter/Exclusion: process.name in ("wuauclt.exe", "gupdate.exe")

• Scenario: Disk Cleanup task initiated by an administrator to free up space
  Filter/Exclusion: process.name == "cleanmgr.exe"

• Scenario: Backup job using Veeam Backup & Replication or Commvault
  Filter/Exclusion: process.name in ("veeam.exe", "cvbackup.exe")

• Scenario: Log file rotation or event log cleanup via PowerShell or LogParser
  Filter/Exclusion: process.name in ("powershell.exe", "logparser.exe") and process.args contains "logrotate" or "eventlog"