RomeoAlfa

Hunt Hypothesis

This hypothesis posits that adversaries are executing specific file-based activities identified by the RomeoAlfa YARA signature to establish persistence or execute initial payloads within the environment. The SOC team should proactively hunt for this behavior in Azure Sentinel to validate the low-severity alert’s context, ensuring that these subtle indicators do not represent early-stage reconnaissance or lateral movement attempts that could escalate if left uninvestigated.

YARA Rule

rule RomeoAlfa
{
	meta:
		copyright = "2015 Novetta Solutions"
		author = "Novetta Threat Research & Interdiction Group - [email protected]"
		Source = "fba0b8bdc1be44d100ac31b864830fcc9d056f1f5ab5486384e09bd088256dd0.file2.bin"

	strings:
	/*
		68 C4 94 41 00     push    offset a0_0_0_0 ; "0.0.0.0"
		56                 push    esi             ; wchar_t *
		E8 1C B4 00 00     call    _wcscpy
		83 C6 28           add     esi, 28h
		83 C4 08           add     esp, 8
		81 FE E8 CD 41 00  cmp     esi, offset unk_41CDE8
		7C E7              jl      short loc_4039DA
	*/

	$zeroIPLoader = {68 [4] 56 E8 [4] 83 C6 28 83 C4 08 81 FE [4] 7C E?}
		


		// push    esi                              
		// mov     esi, [esp+4+a1]                  
		// test    esi, esi                         
		// jle     short loc_403FEB                 
		// push    edi                              
		// mov     edi, ds:Sleep                    
		// push    0EA60h          ; dwMilliseconds 
		// call    edi ; Sleep                      
		// dec     esi                              
		// jnz     short loc_403FE0                 
		// pop     edi                              
		// pop     esi                              
		// retn                                     
		$sleeper  = {5? 8B [3] 85 ?? 7E ?? 5? 8B 3D [4]  68 [4] FF ??  4? 75 ??	5? 5? C3 }
			
		$xercesc = "xercesc"
		
	condition:
		($sleeper 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))
		or $zeroIPLoader 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)))
		and not $xercesc
}

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 3 string patterns in its detection logic.

• Source Rule

False Positive Guidance

Here are 5 specific false positive scenarios for the RomeoAlfa detection rule in an enterprise environment, along with targeted exclusion strategies:

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

  • Context: The SCCM client service (ccmexec.exe) frequently executes scripts and drops temporary binaries into the C:\Windows\CCMCache directory to stage and install software updates. These activities often involve rapid file creation, registry modifications, and process spawning that mimic the behavior patterns detected by the RomeoAlfa YARA rule.
  • Suggested Filter: Exclude processes where the parent executable is ccmexec.exe AND the working directory contains \CCMCache\. Additionally, whitelist the specific hash of the SCCM client service binary to prevent detection on its child processes.

• Scenario: Scheduled Windows Defender Antivirus Real-Time Scanning

  • Context: During peak hours or scheduled maintenance windows, MsMpEng.exe (Windows Defender) performs deep scans that involve reading and decompressing large archives or scanning specific file extensions in real-time. The rule may trigger on the high-volume I/O operations and temporary file handling performed by the antivirus engine itself.
  • Suggested Filter: Create an exclusion for any process with ImageName equal to MsMpEng.exe. Furthermore, exclude events where the source IP is internal (e.g., 10.x.x.x or 192.168.x.x) and the destination port corresponds to standard AV update channels (ports 443/80 for telemetry).

• Scenario: Automated Backup Jobs via Veeam Backup & Replication

  • Context: The VeeamAgentService.exe or associated worker processes run nightly jobs that snapshot virtual machines and transfer data. This involves mounting ISO images, creating