Arcom

Hunt Hypothesis

This detection identifies the execution of the Arcom utility, which adversaries often leverage to establish persistence or manipulate system configurations within Azure environments. Proactively hunting for this behavior is essential because its low-severity classification may cause it to be overlooked in standard alerting, allowing attackers to maintain a stealthy foothold before escalating their activities.

YARA Rule

rule Arcom : RAT
{
	meta:
		author = " Kevin Breen <[email protected]>"
		date = "2014/04"
		ref = "http://malwareconfig.com/stats/Arcom"
		maltype = "Remote Access Trojan"
		filetype = "exe"
        
    strings:
        $a1 = "CVu3388fnek3W(3ij3fkp0930di"
        $a2 = "ZINGAWI2"
        $a3 = "clWebLightGoldenrodYellow"
        $a4 = "Ancestor for '%s' not found" wide
        $a5 = "Control-C hit" wide
        $a6 = {A3 24 25 21}
        
    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 6 string patterns in its detection logic.

• Source Rule

False Positive Guidance

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

• Endpoint Agent Health Checks & Self-Scans

  • Scenario: Enterprise EDR agents (e.g., CrowdStrike Falcon, Microsoft Defender for Endpoint) frequently perform self-integrity scans or configuration updates. During these cycles, the agent’s executable may spawn child processes that match the Arcom YARA signatures (often mimicking legitimate administrative behavior or scanning known binaries).
  • Filter/Exclusion: Exclude process paths containing standard EDR installation directories (e.g., C:\Program Files\CrowdStrike\* or C:\Windows\System32\Microsoft Defender Antivirus\*) and filter out parent processes with names like csagent.exe, MsMpEng.exe, or DefenderSvc.

• Scheduled Group Policy Updates (GPO)

  • Scenario: During business hours, the System Center Configuration Manager (SCCM) or Microsoft Endpoint Configuration Manager pushes software updates and policy changes. The gpupdate service or specific deployment agents may execute scripts that instantiate binaries matching the Arcom rule’s logic for legitimate configuration management tasks.
  • Filter/Exclusion: Create a whitelist based on parent process names associated with GPO enforcement, such as gpsvc.dll, ccmexec.exe, or taskeng.exe. Additionally, exclude events occurring during known maintenance windows (e.g., 02:00–04:00 UTC) where bulk policy refreshes are scheduled.

• IT Helpdesk Remote Support Sessions

  • Scenario: IT administrators utilize remote support tools like BeyondTrust (Bomgar), Citrix Workspace, or Microsoft Remote Desktop Services to troubleshoot user workstations. When an admin connects and initiates a file transfer, registry edit, or script execution