RomeoGolf

Hunt Hypothesis

This hypothesis posits that adversaries are executing the specific malware signature defined by the RomeoGolf YARA rule to establish a foothold within our Azure environment. Proactive hunting for this low-severity indicator is essential to identify early-stage infections before they escalate into more complex lateral movement or data exfiltration campaigns.

YARA Rule

rule RomeoGolf
{
	meta:
		copyright = "2015 Novetta Solutions"
		author = "Novetta Threat Research & Interdiction Group - trig@novetta.com"
		Source = "7322d6b9328a9c708518c99b03a4ed3aa6ba943d7b439f6b1925e6d52a1828fe"

	strings:
	/*
		FF 15 70 80 01 10  call    ds:GetTickCount
		50                 push    eax             ; unsigned int
		E8 80 93 00 00     call    _srand
		83 C4 04           add     esp, 4
		E8 85 93 00 00     call    _rand
		C1 E0 10           shl     eax, 10h
		89 46 0C           mov     [esi+0Ch], eax
		E8 7A 93 00 00     call    _rand
		01 46 0C           add     [esi+0Ch], eax
		E8 72 93 00 00     call    _rand
		C1 E0 10           shl     eax, 10h
		89 46 08           mov     [esi+8], eax
		E8 67 93 00 00     call    _rand
		01 46 08           add     [esi+8], eax
	*/

	$idGen = {FF 15 [4] 50 E8 [4] 83 C4 04 E8 [4] C1 ?? 10 89 [2] E8 [4] 01 [2] E8 [4] C1 ?? 10 89 [2] E8 [4] ?? ?? ?? }
	condition:
		$idGen 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 RomeoGolf detection rule in an enterprise environment, including suggested filters and exclusions:

• Antivirus Real-Time Scanning on Large Data Sets

  • Scenario: The RomeoGolf logic may trigger when the endpoint protection agent (e.g., CrowdStrike Falcon, SentinelOne, or Microsoft Defender for Endpoint) performs a scheduled deep scan of large, static data directories. This often involves reading thousands of files with specific entropy patterns that mimic the YARA signature’s indicators.
  • Filter/Exclusion: Create an exclusion based on the parent process name (e.g., C:\Program Files\Microsoft Defender\MsMpEng.exe or csfalcon.sys) and restrict the rule to only trigger when the file path is outside of known “Data Lake” directories (e.g., exclude paths starting with D:\Archive\).

• Software Deployment via Configuration Management Tools

  • Scenario: During a weekly patching cycle, configuration management tools like Ansible, Chef, or SCCM (System Center Configuration Manager) push updates to workstations. The deployment agents often execute scripts that unpack compressed archives containing binaries with signatures matching the RomeoGolf YARA rule before they are fully registered in the asset inventory.
  • Filter/Exclusion: Add a filter for processes spawned by known management service accounts (e.g., DOMAIN\SCCM-Deploy-Svc) and exclude file paths located within temporary staging folders (e.g., C:\Windows\CCMCache or C:\Temp\Ansible).

• Database Backup and Maintenance Jobs

  • Scenario: Enterprise database administrators run nightly backup jobs using tools like Veeam, Commvault, or native SQL Server Agent. These jobs