asscrypterbysantasdad

Hunt Hypothesis

This detection identifies potential malware activity matching the “asscrypterbysantasdad” signature, which may indicate an adversary employing custom encryption or obfuscation techniques to evade standard defenses. A proactive hunt is essential in Azure Sentinel to uncover early-stage infections that might be missed by high-severity alerts, allowing the SOC team to investigate low-fidelity signals before they escalate into broader compromises.

YARA Rule

rule asscrypterbysantasdad
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 55 8B EC 83 C4 EC 53 [4] 89 45 EC B8 98 40 00 10 E8 AC EA FF FF 33 C0 55 68 78 51 00 10 64 [4] 20 6A 0A 68 88 51 00 10 A1 E0 97 00 10 50 E8 D8 EA FF FF 8B D8 53 A1 E0 97 00 10 50 E8 12 EB FF FF 8B F8 53 A1 E0 97 00 10 50 E8 DC EA FF FF 8B D8 53 E8 DC EA FF FF 8B F0 85 F6 74 26 8B D7 4A B8 F0 97 00 10 E8 C9 E7 FF FF B8 F0 97 00 10 E8 B7 E7 FF FF 8B CF 8B D6 E8 EE EA FF FF 53 E8 98 EA FF FF 8D 4D EC BA 9C 51 00 10 A1 F0 97 00 10 E8 22 EB FF FF 8B 55 EC B8 F0 97 00 10 E8 89 E6 FF FF B8 F0 97 00 10 E8 7F E7 FF FF E8 6E EC FF FF 33 C0 5A 59 59 64 89 10 68 7F 51 00 10 8D 45 EC E8 11 E6 FF FF C3 E9 FF DF FF FF EB F0 5F 5E 5B E8 0D E5 FF FF 00 53 45 54 54 49 4E 47 53 00 00 00 00 FF FF FF FF 1C 00 00 00 45 4E 54 45 52 20 59 4F 55 52 20 4F 57 4E 20 50 41 53 53 57 4F 52 44 20 48 45 52 45 }

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 5 specific false positive scenarios for the asscrypterbysantasdad detection rule, including targeted filters and exclusions suitable for an enterprise environment:

• Scenario: Automated Antivirus Signature Updates

  • Context: Enterprise endpoint protection suites like CrowdStrike Falcon, Microsoft Defender for Endpoint, or Symantec Endpoint Protection frequently download and install new signature definitions. These updates often involve executable files that are digitally signed but may contain compressed payloads or obfuscated logic resembling the “Santasdad” encryption patterns, triggering the YARA rule during the nightly update cycle (typically 02:00–04:00).
  • Filter/Exclusion: Create a process-based exclusion for known AV service executables.
    • Example: Exclude if Process Name = "C:\Program Files\CrowdStrike\csagent.exe" OR "C:\Program Files\Microsoft Defender\MsMpEng.exe" AND Process Command Line contains "--update".

• Scenario: Scheduled System Backup and Encryption Jobs

  • Context: Enterprise backup solutions such as Veeam Backup & Replication, Rubrik, or Commvault run scheduled jobs to compress and encrypt data snapshots. The client agents often spawn temporary processes that utilize encryption libraries similar to those detected by the rule, specifically when processing large volume backups during business hours or off-peak windows.
  • Filter/Exclusion: Exclude specific backup service accounts and their associated agent binaries from detection logic.
    • Example: Exclude if Process Owner = "NT SERVICE\VeeamAgent" OR "VeeamTransportService" AND File Extension in [.vbk, .vbm, .zip].

• Scenario: Software Deployment via Configuration Management Tools

  • Context: IT operations teams use tools like **Microsoft Endpoint Configuration