Based on spreading petya version: 2017-06-28

Hunt Hypothesis

This hunt targets adversaries executing Petya-style ransomware propagation by identifying specific file system modifications and lateral movement patterns characteristic of the June 2017 outbreak within Azure Sentinel logs. Proactively hunting for this behavior is critical because early detection of these spreading signatures allows the SOC team to isolate affected endpoints before encryption spreads across the network, mitigating potential business disruption despite the rule’s current low severity classification.

YARA Rule

rule petya_eternalblue : petya_eternalblue {
    meta:
        author      = "blueliv"
        description =  "Based on spreading petya version: 2017-06-28"
        reference = "https://blueliv.com/petya-ransomware-cyber-attack-is-spreading-across-the-globe-part-2/"
    strings:
        /* Some commands executed by the Petya variant */
       $cmd01 = "schtasks %ws/Create /SC once /TN \"\" /TR \"%ws\" /ST %02d:%0" wide
       $cmd02 = "shutdown.exe /r /f" wide
       $cmd03 = "%s \\\\%s -accepteula -s" wide
       $cmd04 = "process call create \"C:\\Windows\\System32\\rundll32.exe \\\"C:\\Windows\\%s\\\" #1" wide
       /* Strings of encrypted files */
       $str01 = "they have been encrypted. Perhaps you are busy looking" wide
        /* MBR/VBR payload */
        $mbr01 = {00 00 00 55 aa e9 ?? ??}
    condition:
        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 6 string patterns in its detection logic.

References

• https://blueliv.com/petya-ransomware-cyber-attack-is-spreading-across-the-globe-part-2/
• Source Rule

False Positive Guidance

Here are four specific false positive scenarios for the “Spreading Petya” detection rule in an enterprise environment, including suggested filters and exclusions:

• Enterprise Backup Agent Volume Shadow Copy Operations

  • Scenario: Enterprise backup solutions (e.g., Veeam Backup & Replication or Commvault) frequently utilize the vssadmin command or PowerShell scripts to create Volume Shadow Copies before initiating a backup job. This process often triggers the specific registry key modifications and file locking behaviors that mimic Petya’s initial infection phase, particularly when targeting system volumes on domain-joined servers.
  • Filter/Exclusion: Create an exclusion for processes running under the context of known backup service accounts (e.g., NT SERVICE\VeeamTransportService or specific DOMAIN\BackupAdmin) executing commands containing keywords like vssadmin, shadow copy, or wbemcli.

• Scheduled Group Policy Updates and Software Deployment

  • Scenario: During business hours or maintenance windows, System Center Configuration Manager (SCCM) or Microsoft Endpoint Configuration Manager pushes large software updates or Group Policy Objects (GPOs). These deployments often involve mass file writes to the C:\Windows directory and modifications to the HKLM\SOFTWARE\Policies registry hive, which can be misidentified as Petya’s rapid propagation across multiple endpoints.
  • Filter/Exclusion: Exclude events originating from known deployment tools (e.g., ccmexec.exe, msiexec.exe) when they are triggered by scheduled tasks with names containing “SoftwareUpdate,” “GPORefresh,” or specific SCCM collection IDs, specifically during defined maintenance windows.

• Antivirus and EDR Real-Time Scanning Cycles

  • Scenario: Endpoint Detection and Response (EDR) agents like CrowdStrike Falcon, Microsoft Defender for Endpoint, or Symantec Endpoint Protection