SMB Worm Tool

Hunt Hypothesis

This hypothesis posits that adversaries are utilizing specialized SMB worm tools to establish lateral movement footholds within the network by exploiting file sharing protocols. Proactive hunting for this behavior in Azure Sentinel is critical because early identification of these low-severity tool signatures can prevent silent propagation before they escalate into widespread ransomware or data exfiltration incidents.

YARA Rule

rule SMB_Worm_Tool
{
	
	strings:	
		$STR1 = "Global\\FwtSqmSession106829323_S-1-5-19"
		$STR2 = "EVERYONE"
		$STR3 = "y0uar3@s!llyid!07,ou74n60u7f001"
		$STR4 = "\\KB25468.dat" 
	
	condition:
		( uint16(0) == 0x5A4D or 
		  uint16(0) == 0xCFD0 or 
		  uint16(0) == 0xC3D4 or 
		  uint32(0) == 0x46445025 or 
		  uint32(1) == 0x6674725C) 
		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 4 string patterns in its detection logic.

• Source Rule

False Positive Guidance

Here are 5 specific false positive scenarios for the SMB Worm Tool detection rule in an enterprise environment, along with suggested filters or exclusions:

• Microsoft Endpoint Configuration Manager (MECM/SCCM) Software Updates

  • Scenario: The SCCM client service (ccmexec.exe) frequently initiates SMB connections to distribute software updates and patches across the network. During peak update windows, it may spawn child processes that scan or write to shared folders, mimicking the lateral movement behavior of an SMB worm.
  • Filter/Exclusion: Exclude traffic originating from known SCCM management points by filtering for ProcessName containing ccmexec.exe and ParentImage matching the SCCM server FQDN. Additionally, whitelist the specific hash of the SCCM client installer.

• Veeam Backup & Replication Job Execution

  • Scenario: Scheduled backup jobs often utilize SMB protocols to read data from file servers or write backups to shared repositories (e.g., \\BackupServer\Share). The Veeam agent (VeeamAgent.exe or VeeamTransportService) generates high-volume SMB traffic and may spawn temporary helper processes that scan directory structures, triggering the worm detection logic.
  • Filter/Exclusion: Create an exclusion rule for ProcessName matching Veeam* running under the SYSTEM account during defined backup maintenance windows (e.g., 02:00–06:00 local time). Whitelist the specific SMB destination IP ranges associated with the backup repository.

• Group Policy Preferences (GPP) File Deployment

  • Scenario: When Group Policy Objects are refreshed or new GPP items are deployed, the gpupdate service and related worker processes (gpsvc.dll) access shared administrative shares (ADMIN$, C$) to copy configuration