RomeoDelta

Hunt Hypothesis

This detection identifies the execution of specific malicious code patterns defined by the RomeoDelta YARA signature, which may indicate early-stage adversary activity or benign anomalies requiring validation. Proactively hunting for this signal in Azure Sentinel allows the SOC team to correlate these low-severity events with broader telemetry, ensuring that subtle indicators of compromise are not overlooked before they escalate into significant incidents.

YARA Rule

rule RomeoDelta
{
	meta:
		copyright = "2015 Novetta Solutions"
		author = "Novetta Threat Research & Interdiction Group - [email protected]"
		Source = "1df2af99fb3b6e31067b06df07b96d0ed0632f85111541a416da9ceda709237c"

	strings:
	/*
		E8 78 00 00 00  call    GenerateRandomBuffer
		33 C0           xor     eax, eax
		8A 4C 04 04     mov     cl, [esp+eax+24h+buffer]
		80 E9 22        sub     cl, 22h
		80 F1 AD        xor     cl, 0ADh
		88 4C 04 04     mov     [esp+eax+24h+buffer], cl
		40              inc     eax
		83 F8 10        cmp     eax, 10h
		7C EC           jl      short loc_1000117A
		6A 01           push    1               ; fEncode
		8D 54 24 08     lea     edx, [esp+28h+buffer]
		6A 10           push    10h             ; dwDataLength
		52              push    edx             ; pvData
		8B CB           mov     ecx, ebx        ; this
		E8 A2 00 00 00  call    CSocket__Send
	*/

	$loginInit = { E8 [4] 33 C0 8A [3] 80 [2] 80 [2] 88 [3] 40 83 F8 10 7C ?? 6A 01 8D [3] 6A 10 5? 8B CB E8	}

	condition:
		$loginInit 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 RomeoDelta detection rule in an enterprise environment, including suggested filters and exclusions:

• Antivirus Real-Time Scanning on Large File Repositories

  • Scenario: The YARA rule triggers when enterprise-grade antivirus solutions (e.g., CrowdStrike Falcon, SentinelOne, or Microsoft Defender for Endpoint) perform real-time heuristic scanning on large, static file repositories. This often occurs during peak business hours when users access shared drives containing thousands of legacy documents, causing the AV engine to spawn temporary worker processes that match the RomeoDelta signature patterns (e.g., specific memory injection or DLL loading behaviors).
  • Filter/Exclusion: Add a filter to exclude alerts where the parent process is known security software. Specifically, whitelist paths containing \Program Files\CrowdStrike\, \Program Files\SentinelOne\, and \Windows\System32\Microsoft Defender Antivirus\.

• Scheduled Enterprise Patch Deployment via SCCM/Intune

  • Scenario: The rule fires during nightly maintenance windows when Microsoft Endpoint Configuration Manager (SCCM) or Microsoft Intune pushes cumulative updates to the fleet. The deployment agents execute scripts that temporarily modify system binaries and load specific DLLs into memory to verify patch integrity, mimicking the behavioral footprint of the RomeoDelta threat logic before the actual update installation begins.
  • Filter/Exclusion: Create a time-based exclusion for alerts generated between 01:00 and 05:00 UTC on weekdays where the initiating process is ccmexec.exe (SCCM) or IntuneManagementExtension.exe, and the file path matches the software distribution point directory.

• Database Backup Jobs Using Veeam or Commvault

  • Scenario: During automated backup cycles,