ProxyTool3

Hunt Hypothesis

This hypothesis posits that adversaries are utilizing the ProxyTool3 utility to establish covert proxy connections for command and control or data exfiltration within the Azure environment. The SOC team should proactively hunt for this behavior because early identification of ProxyTool3 usage allows analysts to distinguish legitimate administrative traffic from potential stealthy lateral movement before it escalates into a high-severity incident.

YARA Rule

rule ProxyTool3
{
	strings:
		$STR2 = {8A 04 17 8B FB 34 A7 46 88 02 83 C9 FF}
	
	condition:
		(uint16(0) == 0x5A4D or uint16(0) == 0xCFD0 or uint16(0) == 0xC3D4 or uint32(0) == 0x46445025 or uint32(1) == 0x6674725C) and $STR2
}

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 5 specific false positive scenarios for the ProxyTool3 detection rule in an enterprise environment, including suggested filters or exclusions:

• Scenario: Automated Software Deployment via SCCM/Intune

  • Context: The System Center Configuration Manager (SCCM) or Microsoft Intune client service (ccmexec.exe or Microsoft.IntuneManagementService) periodically downloads and installs updates for proxy-aware applications. During this process, the deployment engine may spawn temporary worker processes that mimic the behavior of a custom proxy tool to handle certificate pinning or traffic redirection.
  • Filter/Exclusion: Exclude processes with parent PID belonging to ccmexec.exe or Microsoft.IntuneManagementService, and specifically filter out file paths containing \Program Files\Microsoft Intune Management Extension\ or \SMS_CCM\.

• Scenario: Scheduled Antivirus Definition Updates

  • Context: Enterprise endpoint protection suites like CrowdStrike (Falcon Sensor) or Symantec Endpoint Protection often utilize a dedicated proxy module to fetch definition updates from external repositories. The scheduled job Antimalware Service Executable (MpCmdRun.exe) may trigger the YARA signature when it initializes its internal HTTP/HTTPS proxy handler to bypass local firewall restrictions during peak update windows (e.g., 02:00 AM).
  • Filter/Exclusion: Create an exclusion for the executable path C:\Program Files\Windows Defender\MpCmdRun.exe and any child processes spawned by MsMpEng.exe that contain “Proxy” or “Update” in their command line arguments.

• Scenario: Identity Management Synchronization (Azure AD Connect)

  • Context: The Azure AD Connect service runs scheduled delta synchronization jobs to sync on-premises Active Directory with the cloud. During these cycles, it utilizes a lightweight proxy tool to manage secure communication channels and