WhiskeyCharlie

Hunt Hypothesis

This hypothesis posits that adversaries are utilizing specific file artifacts identified by the WhiskeyCharlie YARA signature to establish persistence or execute initial reconnaissance within the environment. The SOC team should proactively hunt for these indicators in Azure Sentinel to validate the rule’s low-severity alerts against actual threat activity, ensuring early detection of potential lateral movement before it escalates into a critical incident.

YARA Rule

rule WhiskeyCharlie
{
	meta:
		copyright = "2015 Novetta Solutions"
		author = "Novetta Threat Research & Interdiction Group - trig@novetta.com"
		Source = "47ff4f73738acc2f8433dccb2caf980d7444d723ccf2968d69f88f8f96405f96"

	strings:
	/*
		66 89 55 DC     mov     [ebp+SystemTime.wYear], dx
		E8 1E 16 00 00  call    _rand
		6A 0C           push    0Ch
		99              cdq
		59              pop     ecx
		F7 F9           idiv    ecx
		42              inc     edx
		66 89 55 DE     mov     [ebp+SystemTime.wMonth], dx
		E8 0E 16 00 00  call    _rand
		6A 1C           push    1Ch
		99              cdq
		59              pop     ecx
		F7 F9           idiv    ecx
		42              inc     edx
		66 89 55 E2     mov     [ebp+SystemTime.wDay], dx
		E8 FE 15 00 00  call    _rand
		6A 18           push    18h
		99              cdq
		59              pop     ecx
		F7 F9           idiv    ecx
		66 89 55 E4     mov     [ebp+SystemTime.wHour], dx
		E8 EF 15 00 00  call    _rand
		6A 3C           push    3Ch
		99              cdq
		59              pop     ecx
		F7 F9           idiv    ecx
		66 89 55 E6     mov     [ebp+SystemTime.wMinute], dx
		E8 E0 15 00 00  call    _rand
		6A 3C           push    3Ch
		99              cdq
		59              pop     ecx
		F7 F9           idiv    ecx
	*/

	$a = {66 89 55 DC E8 [4] 6A 0C 	99 59 F7 F9 42 66 89 55 DE E8 [4] 6A 1C 99 59 F7 F9 42 66 89 55 E2 E8 [4] 6A 18 99 59 F7 F9 66 89 55 E4 E8 [4] 6A 3C 99 59 F7 F9 66 89 55 E6 E8 [4] 6A 3C 99 59 F7 F9 }

	condition:
		$a 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 4 specific false positive scenarios for the WhiskeyCharlie YARA detection rule in an enterprise environment, including suggested filters and exclusions:

• Antivirus Real-Time Scanning on Large Archives

  • Scenario: Endpoint protection agents (e.g., CrowdStrike Falcon, SentinelOne, or Microsoft Defender) frequently spawn processes to scan large .zip or .tar.gz archives containing thousands of files. During this extraction and scanning phase, the agent’s worker process may exhibit memory patterns or file hash sequences that match the WhiskeyCharlie signature, particularly if the rule looks for specific entropy changes in temporary directories.
  • Filter/Exclusion: Exclude processes running under the service accounts of major EDR vendors (e.g., C:\Program Files\CrowdStrike\csagent.exe, C:\Windows\System32\MsMpEng.exe) when accessing paths within %TEMP% or dedicated scan queues. Additionally, filter alerts where the parent process is the EDR service itself and the file extension is .zip, .7z, or .gz.

• Scheduled Software Distribution via SCCM/Intune

  • Scenario: The Microsoft Endpoint Configuration Manager (MECM/SCCM) or Microsoft Intune deployment engines execute scheduled tasks to push updates, install patches, or deploy new applications. These jobs often extract installer packages (MSI/EXE) into temporary staging folders (C:\Windows\CCMCache) before execution. The rapid creation of temporary files and the specific command-line arguments used by ccmexec.exe or Win32_OptimizationService can trigger the YARA rule if it detects known legitimate deployment signatures as anomalies.
  • Filter/Exclusion: Create a whitelist for the process image paths associated with SCCM (`C:\Windows\CCM\ccmexec.exe