Xtrem RAT v3.5

Hunt Hypothesis

This detection rule identifies the execution of the Xtrem Remote Access Trojan (RAT) version 3.5, which adversaries deploy to establish persistent command-and-control channels and exfiltrate sensitive data from endpoints. Proactively hunting for this specific malware variant in Azure Sentinel is critical because its low severity classification may cause it to be overlooked by standard alerting thresholds, allowing stealthy lateral movement to go undetected until significant compromise occurs.

YARA Rule

rule xtremrat : rat
{
	meta:
		author = "Jean-Philippe Teissier / @Jipe_"
		description = "Xtrem RAT v3.5"
		date = "2012-07-12" 
		version = "1.0" 
		filetype = "memory"

	strings:
		$a = "XTREME" wide
		$b = "XTREMEBINDER" wide
		$c = "STARTSERVERBUFFER" wide
		$d = "SOFTWARE\\XtremeRAT" wide
		$e = "XTREMEUPDATE" wide
		$f = "XtremeKeylogger" wide
		$g = "myversion|3.5" wide
		$h = "xtreme rat" wide nocase
	condition:
		2 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 8 string patterns in its detection logic.

• Source Rule

False Positive Guidance

Here are 4 specific false positive scenarios for the Xtrem RAT v3.5 detection rule in an enterprise environment, including suggested filters and exclusions:

• Antivirus Real-Time Scanning on Large Archives

  • Scenario: The endpoint protection suite (e.g., CrowdStrike Falcon or Microsoft Defender for Endpoint) performs a scheduled deep scan of large compressed archives containing legacy source code. During this process, the AV engine extracts and analyzes executable payloads within .zip or .7z files, triggering the YARA signature due to generic RAT-like strings found in standard development libraries (e.g., libcurl, openssl).
  • Filter/Exclusion: Create a rule exclusion for processes running under the context of the AV service (e.g., C:\Program Files\CrowdStrike\fs.exe or MsMpEng.exe) when they are accessing files with extensions .zip, .7z, or .tar. Additionally, exclude file paths located in designated “Archive” directories.

• Software Deployment via SCCM/Intune

  • Scenario: The IT Operations team executes a mass deployment of the latest Adobe Creative Cloud suite using Microsoft Endpoint Configuration Manager (SCCM). The installation package includes a background installer (AdobeInstaller.exe) that drops temporary DLLs and scripts into %TEMP% which contain obfuscated code resembling the Xtrem RAT’s command-and-control initialization logic.
  • Filter/Exclusion: Exclude file paths matching the pattern C:\Windows\CCMCache\* or C:\ProgramData\Microsoft\Intune Management Extension\*. Furthermore, add a process exclusion for known deployment agents such as ccmexec.exe and msiexec.exe when they are spawning child processes with high entropy scores.

• Automated Backup Verification Jobs

  • **Scenario