APT Malware - Proxy

Hunt Hypothesis

This detection identifies advanced persistent threat (APT) malware establishing proxy connections to exfiltrate data or command and control traffic through network gateways. Proactive hunting is essential in Azure Sentinel to uncover stealthy lateral movements that evade standard perimeter defenses by analyzing proxy logs for anomalous connection patterns indicative of early-stage compromise.

YARA Rule

rule APT_Proxy_Malware_Packed_dev
{
	meta:
		author = "FRoth"
		date = "2014-11-10"
		description = "APT Malware - Proxy"
		hash = "6b6a86ceeab64a6cb273debfa82aec58"
		score = 50
	strings:
		$string0 = "PECompact2" fullword
		$string1 = "[LordPE]"
		$string2 = "steam_ker.dll"
	condition:
		all of them
}

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 3 string patterns in its detection logic.

• Source Rule

False Positive Guidance

Here are 5 specific false positive scenarios for the APT Malware - Proxy detection rule, including tailored filters and exclusions suitable for an enterprise environment:

• Scenario: Automated Patch Management Scans

  • Context: Enterprise patch management tools like Microsoft System Center Configuration Manager (SCCM) or Ivanti Neurons frequently initiate high-volume outbound proxy requests to download update manifests, security definitions, and hotfixes from vendor repositories. These bursts of traffic often mimic the behavior of a compromised host exfiltrating data or communicating with a C2 server.
  • Suggested Filter: Create an exclusion for source IP ranges belonging to the patch management infrastructure (e.g., 10.50.20.0/24) and filter out proxy requests where the User-Agent string contains specific identifiers like SCCM or Ivanti-Update.

• Scenario: Scheduled Cloud Backup Synchronization

  • Context: Automated backup agents such as Veeam Backup & Replication, Rubrik, or Microsoft Azure Backup Agent run nightly scheduled jobs to synchronize metadata and upload incremental backups via the corporate proxy. The consistent, large-volume data transfer patterns can trigger APT exfiltration alerts due to high entropy in the payload size.
  • Suggested Filter: Exclude traffic originating from known backup server subnets (e.g., 192.168.50.0/24) during defined maintenance windows (e.g., 02:00–06:00 local time) where the destination URL matches known cloud storage endpoints (e.g., *.blob.core.windows.net, *.aws.amazon.com).

• Scenario: Endpoint Detection and Response (EDR) Telemetry

  • Context: Modern EDR solutions like CrowdStrike Falcon, **SentinelOne