unknown 1 | SOC Hunt Feed

Hunt Hypothesis

The YARA rule ‘unknown_1’ identifies potential unknown malware artifacts, suggesting the presence of previously unseen malicious files or behaviors. SOC teams should proactively hunt for this in Azure Sentinel to detect and respond to emerging threats before they cause significant damage.

YARA Rule

rule unknown_1: amtrckr
{
	meta:
		family = "unknown"

	condition:
		androguard.url(/222\.76\.213\.20/) or 
		androguard.url(/103\.38\.42\.236/) or 
		androguard.url(/103\.243\.181\.41/) or 
		androguard.url(/123\.1\.157\.4/)
}

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
Source Rule

False Positive Guidance

Scenario: Legitimate software update from a trusted vendor
Description: A known legitimate software update (e.g., Microsoft Windows Update, Adobe Acrobat update) is detected by the YARA rule due to shared string patterns.
Filter/Exclusion: Exclude files signed by Microsoft or Adobe, or use a filter based on the file’s digital signature (file.signer = "Microsoft Corporation" or file.signer = "Adobe Systems Inc.").
Scenario: Scheduled system cleanup task
Description: A scheduled task (e.g., cleanmgr.exe or Disk Cleanup) is flagged due to its file name or behavior matching the YARA rule.
Filter/Exclusion: Exclude processes associated with system maintenance tasks using the process name or parent process (process.name = "cleanmgr.exe" or process.parent.name = "services.exe").
Scenario: Email attachment from a known internal sender
Description: A legitimate email attachment (e.g., a PDF or Word document) from an internal user is flagged as suspicious due to embedded content or file structure.
Filter/Exclusion: Exclude attachments from internal domains using email headers (email.from.domain = "internal.corp"), or use a filter based on file extensions (file.extension = ".pdf" or file.extension = ".docx").
Scenario: Backup file from a file share
Description: A backup file (e.g., backup_2024-10-05.zip) is detected by the YARA rule due to its structure or content.
Filter/Exclusion: Exclude files with a specific naming pattern using a regex filter (e.g., file.name =~ "backup_\d{4}-\d{2}-\d{2}\.zip") or based on the file share path (`file.path = “\backup$*