WhiskeyAlfa

Hunt Hypothesis

This detection targets adversary behavior characterized by specific file artifacts identified through the WhiskeyAlfa YARA signature, indicating potential early-stage reconnaissance or lateral movement activities within the environment. Proactively hunting for these indicators in Azure Sentinel is essential to validate the low-severity alerts against actual threat context and prevent the escalation of dormant threats before they compromise critical assets.

YARA Rule

rule WhiskeyAlfa
{
	meta:
		copyright = "2015 Novetta Solutions"
		author = "Novetta Threat Research & Interdiction Group - trig@novetta.com"
		Source = "1c66e67a8531e3ff1c64ae57e6edfde7bef2352d.ex_"

	strings:
	/*
		E8 77 07 00 00     call    _rand
		B1 FB              mov     cl, 0FBh
		F6 E9              imul    cl
		88 44 34 08        mov     [esp+esi+10008h+randomData], al
		46                 inc     esi
		81 FE 00 00 01 00  cmp     esi, 10000h
		7C EA              jl      short loc_402E8D
	*/

	$randomBuffer = {E8 [4] B1 ?? F6 E9 88 [3] 4? 81 ?? 00 00 01 00 7C}

	/*
		89 58 09              mov     [eax+9], ebx
		C7 40 65 00 00 02 00  mov     dword ptr [eax+65h], 20000h
		C7 40 15 04 00 00 00  mov     dword ptr [eax+15h], 4
		C6 40 08 08           mov     byte ptr [eax+8], 8
		C7 40 04 00 02 00 00  mov     dword ptr [eax+4], 200h
		89 18                 mov     [eax], ebx
		89 58 0D              mov     [eax+0Dh], ebx
		C7 40 11 01 00 00 00  mov     dword ptr [eax+11h], 1
		89 58 69              mov     [eax+69h], ebx
		89 58 19              mov     [eax+19h], ebx
		B8 01 00 00 00        mov     eax, 1
	*/
	$mbrDiskInfo = {89 ?? 09 C7 ?? 65 00 00 02 00 C7 ?? 15 04 00 00 00 C6 ?? 08 08 C7 ?? 04 00 02 00 00 89 ?? 89 ?? 0D C7 ?? 11 01 00 00 00 89 ?? 69 89 ?? 19 B8 01 00 00 00}
		

		// the replacement MBRs in both encoded (XOR 0x53) and decoded form		
		$mbrReplacement_Decoded = { B4 43 B0 00 CD 13 FE C2 80 FA 84 7C F3 B2 80 BF 65 7C 81 05 00 04 83 55 02 00 83 55 04 00 }
		$mbrReplacement_Encoded = { E7 10 E3 53 9E 40 AD 91 D3 A9 D7 2F A0 E1 D3 EC 36 2F D2 56 53 57 D0 06 51 53 D0 06 57 53 }
	
		$licKey = "99E2428CCA4309C68AAF8C616EF3306582A64513E55C786A864BC83DAFE0C78585B692047273B0E55275102C664C5217E76B8E67F35FCE385E4328EE1AD139EA6AA26345C4F93000DBBC7EF1579D4F"
		
	condition:
		$licKey or $mbrReplacement_Decoded or $mbrReplacement_Encoded
		or $randomBuffer 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 $mbrDiskInfo 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 5 string patterns in its detection logic.

• Source Rule

False Positive Guidance

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

• Scenario: Automated Patch Deployment via SCCM/Intune

  • Context: The System Center Configuration Manager (SCCM) or Microsoft Intune agent executes a scheduled patch installation job during maintenance windows. This process often involves the extraction of compressed archives and the execution of temporary scripts that mimic the behavioral patterns WhiskeyAlfa is designed to catch.
  • Suggested Filter/Exclusion: Create an exclusion rule for processes originating from C:\Windows\CCM\ or C:\Program Files (x86)\Microsoft Intune Agent\. Specifically, whitelist the executable hashes of ccmexec.exe, msiexec.exe when launched by SCCM, and any child processes spawned during the “Software Update” deployment cycle.

• Scenario: Endpoint Detection and Response (EDR) Self-Scanning

  • Context: The organization’s primary EDR solution (e.g., CrowdStrike Falcon or SentinelOne) performs a scheduled deep scan or a real-time heuristic analysis. During this activity, the EDR agent injects code into running processes or scans memory regions in a way that triggers the YARA signature within its own execution context.
  • Suggested Filter/Exclusion: Exclude events where the Parent Process Name is the specific EDR service (e.g., csagent.exe, sentinel-agent.exe, or CarbonBlack-140.exe). Additionally, filter out alerts generated when the User Account is a system account like NT AUTHORITY\SYSTEM or LOCAL SERVICE running under these specific parent processes.

• Scenario: Microsoft Office 365 Click-to-Run Updates

  • Context: The O365 Click