WhiskeyDelta

Hunt Hypothesis

This detection identifies adversary behavior characterized by specific code patterns defined in the WhiskeyDelta YARA signature, which may indicate early-stage reconnaissance or benign tool usage often missed by standard alerts. The SOC team should proactively hunt for these indicators within Azure Sentinel to validate false positives and uncover stealthy activities that could precede more significant lateral movement or data exfiltration events.

YARA Rule

rule WhiskeyDelta
{
	meta:
		copyright = "2015 Novetta Solutions"
		author = "Novetta Threat Research & Interdiction Group  [email protected]"
		Source = "41badf10ef6f469dd1c3be201aba809f9c42f86ad77d7f83bc3895bfa289c635"

	strings:
	/*
		F3 A5           rep movsd
		8B 7C 24 30     mov     edi, [esp+28h+arg_4]
		85 FF           test    edi, edi
		7E 3A           jle     short loc_402018
		8B 74 24 2C     mov     esi, [esp+28h+arg_0]
		8A 44 24 08     mov     al, [esp+28h+var_20]
		53              push    ebx
		8A 4C 24 21     mov     cl, [esp+2Ch+var_B]
		8A 5C 24 2B     mov     bl, [esp+2Ch+var_1]
		32 C1           xor     al, cl
		8A 0C 32        mov     cl, [edx+esi]
		32 C3           xor     al, bl
		32 C8           xor     cl, al
		88 0C 32        mov     [edx+esi], cl
		B9 1E 00 00 00  mov     ecx, 1Eh
		8A 5C 0C 0C     mov     bl, [esp+ecx+2Ch+var_20]
		88 5C 0C 0D     mov     [esp+ecx+2Ch+var_1F], bl
		49              dec     ecx
		83 F9 FF        cmp     ecx, 0FFFFFFFFh
		7F F2           jg      short loc_402000
		42              inc     edx
	*/

	$decryption = {F3 A5 8B 7C 24 30 85 FF 7E ?? 8B 74 24 2C 8A 44 24 08 53 8A 4C 24 21 8A 5C 24 2B 32 C1 8A 0C 32 32 C3 32 C8 88 0C 32 B9 1E 00 00 00 8A 5C 0C 0C 	88 5C 0C 0D 49 	83 F9 FF 7F ?? 	42 }

	$s1 = "=====IsFile=====" wide
	$s2 = "=====4M=====" wide
	$s3 = "=====IsBackup=====" wide
	
	condition:
		2 of ($s*) 
		or $decryption 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 4 string patterns in its detection logic.

• Source Rule

False Positive Guidance

Here are 4 specific false positive scenarios for the WhiskeyDelta detection rule in an enterprise environment, along with recommended filters and exclusions:

• Endpoint Protection Policy Updates via CrowdStrike Falcon

  • Scenario: The CrowdStrike Falcon Sensor performs a scheduled nightly update of its definition database. This process spawns a temporary executable that writes new signature files to the %ProgramData%\CrowdStrike\ directory, triggering the WhiskeyDelta rule due to the creation of multiple high-entropy files in a short window.
  • Filter/Exclusion: Exclude file paths containing \CrowdStrike\ and restrict the detection to trigger only when the parent process is NOT csagent.exe. Additionally, add an exclusion for the specific SHA256 hash of the known update utility binary used by CrowdStrike.

• Microsoft SCCM (MECM) Application Deployment

  • Scenario: During a business-hours maintenance window, System Center Configuration Manager deploys a new line-of-business application to 500 workstations. The deployment agent (ccmexec.exe) extracts installation packages and writes temporary configuration files to %Temp% before executing the installer, mimicking the behavior of an unknown process writing unexpected artifacts.
  • Filter/Exclusion: Create a whitelist for the parent process ccmexec.exe (Microsoft Configuration Manager). Furthermore, exclude any file creation events where the source path contains \CCMCache\ or \AppData\Local\Temp\, as these are standard staging areas for SCCM deployments.

• Automated Log Rotation and Archiving by Splunk Universal Forwarder

  • Scenario: A scheduled task runs every 15 minutes to rotate application logs. The Splunk Universal Forwarder compresses large log files into .gz archives and moves them to a network share. This activity generates new file handles and writes compressed