PcSharev40

Hunt Hypothesis

This detection identifies potential file-sharing activities or specific malware signatures associated with the PcSharev40 YARA rule, which may indicate early-stage lateral movement or data exfiltration attempts within the environment. Proactively hunting for this behavior in Azure Sentinel allows the SOC team to validate low-severity alerts that could otherwise be overlooked, ensuring timely identification of subtle threats before they escalate into significant incidents.

YARA Rule

rule PcSharev40
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 55 8B EC 6A FF 68 90 34 40 00 68 B6 28 40 00 64 A1 }

condition:
		$a0 at pe.entry_point
}

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.

• Source Rule

False Positive Guidance

Here are 5 specific false positive scenarios for the PcSharev40 detection rule, including suggested filters and exclusions tailored for an enterprise environment:

• Scenario: Legitimate deployment of Microsoft Office updates via Microsoft Endpoint Configuration Manager (MECM/SCCM).

  • Context: The OfficeC2RClient.exe or Setup.exe process often creates temporary shared folders in the %TEMP% directory to distribute update packages, mimicking the behavior of a file-sharing tool.
  • Filter/Exclusion: Create an exclusion for processes named OfficeC2RClient.exe, Setup.exe, and Microsoft.Update.Client.exe when they are located within the path C:\Program Files\Microsoft Office* or C:\Windows\System32.

• Scenario: Automated backup jobs executed by Veeam Backup & Replication or Rubrik.

  • Context: During scheduled backup windows, these agents frequently mount virtual disks and share temporary staging folders to stage data before compression, triggering the YARA rule’s file-sharing signature.
  • Filter/Exclusion: Exclude processes Veeam.Backup.Service.exe, vbrservice.exe, and RubrikAgent.exe when running under the context of the SYSTEM or a dedicated service account (e.g., DOMAIN\BackupSvc).

• Scenario: Execution of System Center Configuration Manager (SCCM) application deployments for third-party software.

  • Context: When deploying applications like Adobe Acrobat or Zoom, SCCM creates a temporary network share (\\<Server>\DeployApps) to distribute installers to endpoints, which the YARA rule may flag as unauthorized sharing behavior.
  • Filter/Exclusion: Filter out events where the parent process is ccmsetup.exe or ccmexec.exe, specifically when the