Regla para detectar Ransom.Alpha (posibles falsos positivos)

Hunt Hypothesis

This hunt hypothesis targets potential Ransom Alpha ransomware activity by identifying specific file encryption patterns that may initially trigger false positives due to benign administrative tasks. The SOC team should proactively investigate these signals in Azure Sentinel to distinguish between legitimate operations and early-stage ransomware execution, ensuring rapid containment before data loss occurs.

YARA Rule

rule Ransom_Alpha
{
meta:
description = "Regla para detectar Ransom.Alpha (posibles falsos positivos)"
author = "CCN-CERT"
version = "1.0"
strings:
$a = { 52 00 65 00 61 00 64 00 20 00 4D 00 65 00 20 00 28 00 48 00 6F 00 77 00 20 00 44 00 65 00 63 }
condition:
$a
}

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 5 specific false positive scenarios for the Ransom.Alpha detection rule in an enterprise environment, including suggested filters and exclusions:

• Enterprise Backup Agent File Locking & Encryption

  • Scenario: The Ransom.Alpha rule triggers when a backup agent (e.g., Veeam Backup & Replication, Commvault, or Microsoft Azure Backup) performs its scheduled nightly job. These agents often encrypt large volumes of data on the source server simultaneously, mimicking ransomware behavior by modifying file extensions and locking handles across thousands of files in a short window.
  • Suggested Filter/Exclusion: Create an exclusion list for known backup service accounts (e.g., DOMAIN\VeeamService, SYSTEM) and specific process paths (e.g., C:\Program Files\Commvault\SimAgent\bin\simagent.exe). Additionally, exclude events occurring during the defined maintenance window (e.g., 02:00–04:00 UTC) for these specific hosts.

• Patch Management and Software Deployment Tools

  • Scenario: Automated deployment tools like Microsoft SCCM (Configuration Manager), Ivanti, or Ansible execute mass software updates or configuration changes. During a “push” event, these tools may overwrite system files, update registry keys, and encrypt application binaries across multiple endpoints simultaneously, triggering the high-volume file modification logic of Ransom.Alpha.
  • Suggested Filter/Exclusion: Exclude processes associated with known deployment engines (e.g., ccmexec.exe, IvantiAgent.exe, ansible-runner). Implement a filter that suppresses alerts if the parent process is running under a scheduled task context (e.g., Task Name contains “PatchDeployment” or “SoftwareUpdate”).

• Antivirus and EDR Real-Time Scanning

  • Scenario: The