unrecom

Hunt Hypothesis

This detection identifies the execution of unregistered or unrecognized commands that deviate from standard baseline activity, potentially signaling early-stage reconnaissance or lateral movement by an adversary. Proactively hunting for these anomalies in Azure Sentinel is critical to uncover stealthy threats that bypass traditional signature-based defenses before they escalate into significant incidents.

YARA Rule

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

	strings:
		$meta = "META-INF"
		$conf = "load/ID"
		$a = "load/JarMain.class"
		$b = "load/MANIFEST.MF"
        $c = "plugins/UnrecomServer.class"

	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 5 string patterns in its detection logic.

• Source Rule

False Positive Guidance

Here are 4 specific false positive scenarios for the unrecom detection rule in an enterprise environment, along with suggested filters or exclusions:

• Microsoft Endpoint Configuration Manager (SCCM) Application Deployment

  • Scenario: The SCCM agent (ccmexec.exe) frequently executes PowerShell scripts to deploy new applications or update configurations. These scripts often spawn temporary processes that load unsigned or self-signed DLLs, which the unrecom YARA rule may flag as “unrecognized” code execution before the digital signature is fully validated by the OS.
  • Suggested Filter: Exclude process paths containing \Microsoft\CCM\ and parent processes named ccmexec.exe. Additionally, add a filter for any child process where the file age is less than 24 hours to allow for initial deployment noise.

• Scheduled Antivirus Real-Time Scanning (e.g., CrowdStrike or SentinelOne)

  • Scenario: During peak business hours, the endpoint protection agent (cs.exe for CrowdStrike or osd.exe for SentinelOne) performs deep heuristic scans. This involves spawning temporary worker threads that inject code into running user sessions to analyze memory structures, triggering the rule due to the dynamic nature of these injection artifacts which may not match static signature databases immediately.
  • Suggested Filter: Create an exclusion list for known security vendor executables (e.g., csagent.exe, osd.exe, MsMpEng.exe) and their child processes. Specifically, exclude events where the command line arguments contain keywords like /scan, /heuristic, or /inject.

• Automated Database Maintenance Jobs (SQL Server Agent)

  • Scenario: The SQL Server Agent service (sqlagent.exe) runs nightly maintenance plans that execute stored procedures via sqlcmd or custom PowerShell wrappers. These jobs often invoke temporary compiled assemblies to handle data