PolyBoxCAnskya

Hunt Hypothesis

This detection identifies potential malicious activity associated with the PolyBoxCAnskya signature, which may indicate the presence of specific malware or suspicious artifacts within the environment. Proactively hunting for this behavior in Azure Sentinel allows the SOC team to validate low-severity alerts and uncover early-stage threats that might otherwise be overlooked by automated triage processes.

YARA Rule

rule PolyBoxCAnskya
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 55 8B EC 83 C4 F0 53 56 B8 E4 41 00 10 E8 3A E1 FF FF 33 C0 55 68 11 44 00 10 64 FF 30 64 89 20 EB 08 FC FC FC FC FC FC 27 54 6A 0A 68 20 44 00 10 A1 1C 71 00 10 50 E8 CC E1 [4] 85 DB 0F 84 77 01 00 00 53 A1 1C 71 00 10 50 E8 1E E2 FF FF 8B F0 85 F6 0F 84 61 01 00 00 53 A1 1C 71 00 10 50 E8 E0 E1 FF FF 85 C0 0F 84 4D 01 00 00 50 E8 DA E1 FF FF 8B D8 85 DB 0F 84 3D 01 00 00 56 B8 70 80 00 10 B9 01 00 00 00 8B 15 98 41 00 10 E8 9E DE FF FF 83 C4 04 A1 70 80 00 10 8B CE 8B D3 E8 E1 E1 FF FF 6A 00 6A 00 A1 70 80 00 10 B9 30 44 00 10 8B D6 E8 F8 FD FF FF }

condition:
		$a0
}

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 4 specific false positive scenarios for the PolyBoxCAnskya detection rule in an enterprise environment, along with suggested filters and exclusions:

• Scenario: Scheduled Antivirus or EDR Scans on Shared Drives

  • Context: Enterprise Endpoint Detection and Response (EDR) solutions like CrowdStrike Falcon or Microsoft Defender for Endpoint often perform scheduled deep scans of shared network drives (e.g., \\FileServer\HR_Docs). The YARA rule may match the scanning engine’s temporary file creation or memory signature against the “Anskya” logic.
  • Suggested Filter/Exclusion: Create an exclusion based on the process name and path. Exclude any event where the parent process is MsMpEng.exe (Microsoft Defender) or FalconSensorService.exe (CrowdStrike) running under the context of a scheduled task named “Daily Deep Scan”.
  • Filter Logic: ProcessName IN ("MsMpEng.exe", "FalconSensorService.exe") AND ParentProcessName = "TaskScheduler"

• Scenario: Automated Backup Operations by Veeam or Commvault

  • Context: During nightly backup windows, tools like Veeam Backup & Replication or Commvault generate temporary staging files and mount virtual disk images. These operations often involve rapid file I/O and memory allocation patterns that mimic the behavior detected by PolyBoxCAnskya, particularly when processing large archives containing embedded scripts.
  • Suggested Filter/Exclusion: Exclude events originating from backup service accounts (e.g., vbrsvc, commagent) running on dedicated backup servers or during specific maintenance windows (e.g., 02:00–06:00 UTC).
  • Filter Logic: `(ProcessName IN (“vbrservice.exe”, ”