misc pos

Hunt Hypothesis

This hypothesis targets adversaries attempting to execute malicious payloads with non-standard or obfuscated Portable Executable (PE) structures that may evade signature-based defenses. Proactively hunting for these anomalies in Azure Sentinel is critical because they often indicate early-stage fileless attacks or living-off-the-land techniques where attackers leverage legitimate tools with modified binaries to maintain persistence while avoiding initial detection triggers.

YARA Rule

rule misc_pos
{
meta:
	author = "@patrickrolsen"
	reference = "POS Malware"
strings:
	$s1 = "KAPTOXA"
	$s2 = "cmd /c net start %s"
	$s3 = "pid:"
	$s4 = "%ADD%"
	$s5 = "COMSPEC"
	$s6 = "KARTOXA"
condition:
	uint16(0) == 0x5A4D and 3 of ($s*)
}

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.

References

• POS Malware
• Source Rule

False Positive Guidance

Here are 5 specific false positive scenarios for the misc_pos YARA detection rule in an enterprise environment, including suggested filters and exclusions:

• Antivirus Real-Time Scanning and On-Demand Updates

  • Scenario: The YARA rule triggers on legitimate binary execution or file modification events generated by endpoint protection suites (e.g., CrowdStrike Falcon, SentinelOne, or Microsoft Defender) during scheduled definition updates or real-time scan cycles. These tools frequently spawn temporary processes that match the generic signatures defined in misc_pos.
  • Filter/Exclusion: Exclude process paths containing known AV directories and specific executable names (e.g., C:\Program Files\Microsoft Defender\*, CrowdStrike\csfalcon.exe, SentinelOne\Sentinel.exe). Additionally, filter out events where the parent process is the AV service itself.

• Enterprise Patch Management Deployments

  • Scenario: Automated patching tools like WSUS (Windows Server Update Services), Ivanti, or SCCM (System Center Configuration Manager) trigger the rule when deploying security updates to workstations. The deployment agents often extract temporary files and execute installation scripts that mimic the behavior patterns detected by misc_pos.
  • Filter/Exclusion: Create an exclusion for processes launched by known patch management agents (e.g., ccmexec.exe, wsusagent.exe, IvantiAgentService). Filter events occurring during defined maintenance windows (e.g., 02:00–04:00 UTC) where the user context is a system account (e.g., NT AUTHORITY\SYSTEM or LOCAL SERVICE).

• Scheduled Backup and Data Archiving Jobs

  • Scenario: Enterprise backup solutions such as Veeam Backup & Replication, Commvault, or **Rub