VxModificationofHi924

Hunt Hypothesis

This hypothesis targets potential malicious modifications to high-privilege or critical system components, as indicated by the YARA rule signature, which may signal an adversary attempting to alter execution logic or hide their presence. Proactively hunting for these specific file modifications in Azure Sentinel allows the SOC to identify subtle tampering or persistence mechanisms that standard integrity checks might miss, reducing the risk of undetected compromise in critical workloads.

YARA Rule

rule VxModificationofHi924
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 50 53 51 52 1E 06 9C B8 21 35 CD 21 53 BB [2] 26 [2] 49 48 5B }

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

• Scenario: A system administrator uses a custom PowerShell script or a tool like Sysinternals (e.g., PSTools) to modify the Hi924 registry key (or a similar high-value identifier) to adjust system performance settings or enable debug features during a maintenance window.
  • Filter/Exclusion: Exclude processes originating from powershell.exe or pwsh.exe if the parent process is cmd.exe or an interactive user session, and the command line contains keywords like -Set, -Add, or specific parameter names associated with configuration changes.
• Scenario: A scheduled task runs a third-party application installer or updater (e.g., 7-Zip, Notepad++, or a Java-based agent) that writes configuration data to the registry under keys that match the Hi924 pattern as part of its standard initialization or update routine.
  • Filter/Exclusion: Exclude processes whose image path resides in known application directories (e.g., C:\Program Files\, C:\Program Files (x86)\) and are launched by Task Scheduler (svchost.exe with Taskschd service) or explorer.exe with a user-initiated context menu action.
• Scenario: A legitimate backup or snapshot tool (e.g., Veeam, Acronis, or Windows Server Backup) performs a registry backup or restore operation that temporarily modifies or rewrites registry keys, including those matching the Hi924 signature, to ensure consistency.
  • Filter/Exclusion: Exclude processes with image names matching known backup agents (e.g., vssadmin.exe, wbadmin.exe, veeam.exe, acronis.exe) or those running under a service account with the Backup Operators group membership.