Check if hotfix are applied

Hunt Hypothesis

Adversaries may exploit unpatched systems by leveraging known vulnerabilities in missing hotfixes, making proactive hunting for missing patches critical to identifying potential attack vectors. SOC teams should actively search for unapplied hotfixes in Azure Sentinel to detect and mitigate risks associated with outdated system configurations.

YARA Rule

rule check_patchlevel {
    meta:
        author = "x0r"
        description = "Check if hotfix are applied"
	version = "0.1"
    strings:
        $p1 = "SOFTWARE\\Microsoft\\Windows NT\\CurrentVersion\\Hotfix" nocase
    condition:
        any 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 1 string patterns in its detection logic.

• Source Rule

False Positive Guidance

• Scenario: System updates via Microsoft Update
  Filter/Exclusion: Exclude events related to Microsoft Update by checking the Event ID (e.g., 19 or 20) or using the Product field to filter out Microsoft Windows updates.

• Scenario: Patch deployment via SCCM (System Center Configuration Manager)
  Filter/Exclusion: Use the Source field to exclude events originating from SCCM or apply a filter based on the Deployment ID or Patch Name associated with SCCM.

• Scenario: Scheduled maintenance tasks (e.g., Task Scheduler running a script)
  Filter/Exclusion: Exclude tasks that are known maintenance scripts by checking the Task Name or User field (e.g., System or Administrators) and filtering out known maintenance scripts.

• Scenario: Automated patching via third-party tools (e.g., Patch Manager, Altiris)
  Filter/Exclusion: Use the Process Name or Application Name to exclude known patching tools (e.g., PatchManager.exe, AltirisAgent.exe) or apply a filter based on the Vendor or Tool Name.

• Scenario: Manual patch installation by an administrator (e.g., using Windows Update or Group Policy)
  Filter/Exclusion: Exclude events where the User field indicates an administrator performing a manual patch, or use the Event Source to filter out Windows Update or Group Policy related events.