AINEXEv21

Hunt Hypothesis

This detection identifies potential malicious executable behavior through a specific YARA signature (AINEXEv21), signaling the presence of known threat patterns within the environment. Proactive hunting for this indicator in Azure Sentinel is essential to validate its prevalence across endpoints and uncover any associated lateral movement or persistence mechanisms that may have been missed by standard alerting thresholds.

YARA Rule

rule AINEXEv21
{
      meta:
		author="malware-lu"
strings:
		$a0 = { A1 [2] 2D [2] 8E D0 BC [2] 8C D8 36 A3 [2] 05 [2] 36 A3 [2] 2E A1 [2] 8A D4 B1 04 D2 EA FE C9 }

condition:
		$a0 at pe.entry_point
}

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

Here are 3-5 specific false positive scenarios for the AINEXEv21 detection rule, including context and recommended filters or exclusions:

• Scenario: Automated Antivirus Definition Updates via Local Service

  • Context: The local Windows Defender or third-party EDR agent (e.g., CrowdStrike Falcon, SentinelOne) executes a scheduled task to download and install virus definition updates. This process often spawns child processes that match the heuristic patterns of AINEXEv21 due to file extraction and memory injection behaviors during the update cycle.
  • Filter/Exclusion: Create a process exclusion for the specific antivirus service executable (e.g., MsMpEng.exe or C:\Program Files\CrowdStrike\fs_qt_service.exe) running under the SYSTEM account, specifically when the parent process is the Windows Update Service (wuauserv).

• Scenario: Enterprise Software Deployment via SCCM/Intune

  • Context: During a scheduled software deployment window, Microsoft Endpoint Configuration Manager (SCCM) or Intune pushes new applications to endpoints. The installation agent extracts compressed payloads and registers services, triggering the YARA rule due to the presence of temporary extraction folders and rapid file creation patterns typical of AINEXEv21 signatures.
  • Filter/Exclusion: Exclude processes initiated by ccmsetup.exe (SCCM) or IntuneManagementExtension.exe where the command line contains keywords like “install,” “deploy,” or “update,” and restrict this exclusion to business hours (08:00–18:00).

• Scenario: Scheduled Backup Agent Operations

  • Context: Enterprise backup solutions such as Veeam Agent for Windows or Acronis Cyber Protect run nightly jobs that compress data and write to disk. The compression engine creates temporary memory-mapped files and spawns helper