Zegost Trojan

Hunt Hypothesis

This hunt targets the initial execution and persistence behaviors of the Zegost Trojan to identify early-stage compromise indicators that may be masked by its low severity classification. Proactively hunting for this threat in Azure Sentinel is critical to validate detection efficacy across diverse workloads and prevent potential lateral movement before the adversary establishes deeper footholds within the environment.

YARA Rule

rule Zegost : Trojan
{
	meta:
		author="Kevin Falcoz"
		date="10/06/2013"
		description="Zegost Trojan"
		
	strings:
		$signature1={39 2F 66 33 30 4C 69 35 75 62 4F 35 44 4E 41 44 44 78 47 38 73 37 36 32 74 71 59 3D}
		$signature2={00 BA DA 22 51 42 6F 6D 65 00}
		
	condition:
		$signature1 and $signature2
}

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 2 string patterns in its detection logic.

• Source Rule

False Positive Guidance

Here are 4 specific false positive scenarios for the Zegost Trojan detection rule in an enterprise environment, including suggested filters and exclusions:

• Scenario: Automated Software Updates via Windows Update or SCCM

  • Context: The Zegost Trojan often mimics legitimate update behaviors. When Microsoft Endpoint Configuration Manager (SCCM) or the native WindowsUpdate service pushes critical patches to endpoints, it may trigger the rule due to the creation of temporary files in %TEMP%, network connections to known update servers, and execution of signed binaries (wuauclt.exe or ccmexec.exe) that match the Trojan’s behavioral signature.
  • Filter/Exclusion: Create an exclusion for processes originating from the specific file paths of SCCM agents (e.g., C:\Program Files\Microsoft Configuration Manager\bin\x64\ccmexec.exe) and Windows Update components (%SystemRoot%\SoftwareDistribution). Additionally, filter out network traffic destined for Microsoft update content delivery networks (CDNs) if the detection includes network flow analysis.

• Scenario: Scheduled Antivirus Scans by Enterprise EDR Solutions

  • Context: During scheduled deep scans, Endpoint Detection and Response (EDR) tools like CrowdStrike Falcon, SentinelOne, or Microsoft Defender for Endpoint often spawn multiple child processes to analyze file integrity. The Zegost detection logic may flag these rapid process creations and the subsequent scanning of large file volumes as suspicious activity resembling a Trojan establishing persistence.
  • Filter/Exclusion: Exclude alerts where the parent process is the primary EDR service (e.g., C:\Program Files\CrowdStrike\FalconSensor\CSFalconService.exe or MsMpEng.exe). Implement a time-based filter to suppress these alerts during known maintenance windows (e.g., 02:00 – 04