VirusRat

Hunt Hypothesis

This hypothesis posits that adversaries are deploying the VirusRat malware to establish persistent command-and-control channels and exfiltrate sensitive data within the Azure environment. Proactive hunting is essential because, despite its current low severity classification, early identification of this specific YARA signature allows the SOC team to isolate compromised endpoints before lateral movement or significant data loss occurs.

YARA Rule

rule VirusRat : RAT
{
	meta:
		author = " Kevin Breen <kevin@techanarchy.net>"
		date = "2014/04"
		ref = "http://malwareconfig.com/stats/VirusRat"
		maltype = "Remote Access Trojan"
		filetype = "exe"

	strings:
		$string0 = "virustotal"
		$string1 = "virusscan"
		$string2 = "abccba"
		$string3 = "pronoip"
		$string4 = "streamWebcam"
		$string5 = "DOMAIN_PASSWORD"
		$string6 = "Stub.Form1.resources"
		$string7 = "ftp://{0}@{1}" wide
		$string8 = "SELECT * FROM moz_logins" wide
		$string9 = "SELECT * FROM moz_disabledHosts" wide
		$string10 = "DynDNS\\Updater\\config.dyndns" wide
		$string11 = "|BawaneH|" wide

	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 12 string patterns in its detection logic.

• Source Rule

False Positive Guidance

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

• Endpoint Protection Engine Scanning & Quarantine Operations

  • Scenario: The primary antivirus engine (e.g., CrowdStrike Falcon, SentinelOne, or Microsoft Defender) performs a scheduled deep scan. During this process, the engine’s core executable (csfalcon.exe, s1agent.exe, or MsMpEng.exe) spawns child processes to analyze and quarantine files in real-time. These behaviors often mimic VirusRat’s command-and-control (C2) communication patterns and file manipulation signatures.
  • Filter/Exclusion: Create an exclusion rule that ignores alerts where the parent process is a known EDR agent executable AND the destination IP belongs to the vendor’s cloud update/C2 infrastructure (e.g., *.crowdstrike.com, *.sentinelone.net).

• Enterprise Software Deployment via Configuration Management

  • Scenario: Automated patching and software deployment tools like Microsoft SCCM/MECM, Ivanti Endpoint Manager, or Ansible Tower execute scheduled tasks to push updates. These agents often download payloads, extract archives, and modify registry keys in a manner that triggers the VirusRat YARA signatures for “suspicious file execution” and “network beaconing.”
  • Filter/Exclusion: Exclude alerts where the process path contains standard deployment directories (e.g., C:\Program Files\Microsoft Configuration Manager, C:\Ivanti) or where the command line arguments include specific deployment flags (e.g., /deploy, --task-id=patch_cycle).

• IT Administration and Remote Management Sessions

  • Scenario: System administrators utilize remote management tools such as TeamViewer, AnyDesk, or **Microsoft SCC