Regla para detectar el dropper de Ransom.Satana

Hunt Hypothesis

This hunt hypothesis targets adversaries deploying the Ransom.Satana dropper to establish initial footholds and execute early-stage ransomware payloads within Azure Sentinel environments. Proactively hunting for this behavior is critical because detecting the dropper at a low severity stage allows the SOC team to isolate compromised assets before the full encryption phase of the ransomware attack begins.

YARA Rule

rule Ransom_Satana_Dropper
{
    meta:
        description = "Regla para detectar el dropper de Ransom.Satana"
        author = "CCN-CERT"
        version = "1.0"
    strings:
        $a = { 25 73 2D 54 72 79 45 78 63 65 70 74 }
        $b = { 64 3A 5C 6C 62 65 74 77 6D 77 79 5C 75 69 6A 65 75 71 70 6C 66 77 75 62 2E 70 64 62 }
        $c = { 71 66 6E 74 76 74 68 62 }
    condition:
        all 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 3 string patterns in its detection logic.

• Source Rule

False Positive Guidance

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

• Enterprise Endpoint Management Updates (Microsoft Intune/SCCM)

  • Scenario: The deployment of a new security patch or application update via Microsoft Endpoint Configuration Manager (MECM) or Intune triggers the installation of a temporary executable (msiexec.exe spawning setup.exe) that writes files to %TEMP% and modifies registry keys, mimicking the dropper behavior of Ransom.Satana.
  • Filter/Exclusion: Exclude processes where the parent process is ccmexec.exe or MicrosoftEdgeUpdate.exe, and filter for file paths containing \Program Files\Microsoft Intune\Agent\. Additionally, whitelist certificates signed by “Microsoft Corporation” if the dropper logic checks digital signatures.

• Scheduled Antivirus Definition Updates (CrowdStrike/Symantec)

  • Scenario: A scheduled nightly job runs an antivirus engine update (e.g., CrowdStrike Falcon Sensor or Symantec Endpoint Protection). This process downloads a compressed archive, extracts it to a local staging folder, and executes a self-modifying installer to apply new signatures, which generates file creation and execution patterns identical to the Ransom.Satana dropper logic.
  • Filter/Exclusion: Create an exclusion for processes with image paths matching C:\Program Files\CrowdStrike\* or C:\Program Files\Symantec Endpoint Protection\*. Specifically, filter out events where the parent process is falcon.sysmon.exe (CrowdStrike) and the action occurs during the defined maintenance window (e.g., 02:00 – 04:00 local time).

• Software Deployment via Chocolatey or SCCM

  • Scenario: