RomeoWhiskey Two

Hunt Hypothesis

This detection identifies the execution of specific malicious payloads defined by the RomeoWhiskey_Two YARA signature, indicating potential early-stage adversary activity such as dropper or initial access mechanisms. Proactively hunting for this behavior in Azure Sentinel is critical to uncover low-severity indicators that may have been missed by automated alerts, allowing the SOC team to validate threat presence before it escalates into a full-blown incident.

YARA Rule

rule RomeoWhiskey_Two
{
	meta:
		copyright = "2015 Novetta Solutions"
		author = "Novetta Threat Research & Interdiction Group - [email protected]"
		Source = "a8d88714f0bc643e76163d1b8972565e78a159292d45a8218d0ad0754c8f561d"

	strings:
	/*
		FF 15 78 A2 00 10  call    GetTickCount_9
		66 8B C8           mov     cx, ax

		// the next op is a mov or a push/pop depending on the code version
		53                 push    ebx
		8F 45 F4           pop     dword ptr [ebp-0Ch]
		//or
		89 5D F4           mov     dword ptr [ebp+var_C], ebx
		
		
		66 81 F1 40 1C     xor     cx, 1C40h
		66 D1 E9           shr     cx, 1
		81 C1 E0 56 00 00  add     ecx, 56E0h
		0F B7 C9           movzx   ecx, cx
		0F B7 C0           movzx   eax, ax
		81 F1 30 32 00 00  xor     ecx, 3230h
		C1 E0 10           shl     eax, 10h
		0B C8              or      ecx, eax
	*/

	$a = {FF 15 [4] 66 8B C8 [3-4] 	66 81 F1 40 1C 	66 D1 E9 81 C1 E0 56 00 00 0F B7 C9 0F B7 C0 81 F1 30 32 00 00 	C1 E0 10 0B C8 }

	condition:
		$a in ((pe.sections[pe.section_index(".text")].raw_data_offset)..(pe.sections[pe.section_index(".text")].raw_data_offset + pe.sections[pe.section_index(".text")].raw_data_size))
}

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 RomeoWhiskey Two detection rule in an enterprise environment, including suggested filters and exclusions:

• Antivirus Signature Updates via Windows Update Agent

  • Scenario: The WindowsUpdate service (or third-party agents like Microsoft Defender Antivirus) frequently downloads and executes signature definition updates. These processes often spawn child processes with similar naming conventions or memory injection patterns that mimic the behavior RomeoWhiskey Two is designed to catch, particularly when updating the MpCmdRun.exe or MsMpEng.exe binaries.
  • Suggested Filter: Exclude alerts where the parent process is svchost.exe (specifically the WindowsUpdate service) and the file path resides within C:\ProgramData\Microsoft\Windows Defender\Definition Updates.

• Scheduled Group Policy Preferences Deployment

  • Scenario: During business hours or maintenance windows, the Group Policy Client Service (gpsvc) executes scheduled tasks to apply registry modifications or copy files across endpoints. Tools like SCCM (System Center Configuration Manager) often trigger these deployments, which can involve writing temporary scripts and executing them in a manner that triggers the YARA rule’s heuristic for suspicious script execution.
  • Suggested Filter: Create an exclusion for processes launched by gpupdate.exe or ccmexec.exe where the command line arguments contain flags related to policy application (e.g., /target:computer, /force) and the file hash matches a known enterprise baseline.

• Enterprise Backup Software Operations

  • Scenario: Scheduled backup jobs using tools like Veeam Agent, Commvault, or Acronis Cyber Protect often perform real-time scanning and data indexing. These applications frequently spawn temporary worker processes that read large volumes of files and inject code into running services to ensure data integrity, a