SexeCrypter11bysantasdad

Hunt Hypothesis

This detection identifies potential fileless or memory-based malware activity associated with the “SexeCrypter11bysantasdad” signature, which may indicate early-stage encryption or payload execution often seen in ransomware campaigns. A proactive hunt is essential to validate these low-severity alerts and uncover hidden lateral movement or data staging behaviors that could precede a larger incident within the Azure Sentinel environment.

YARA Rule

rule SexeCrypter11bysantasdad
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 55 8B EC 83 C4 EC 53 56 57 33 C0 89 45 EC B8 D8 39 00 10 E8 30 FA FF FF 33 C0 55 68 D4 3A 00 10 64 FF 30 64 89 [4] E4 3A 00 10 A1 00 57 00 10 50 E8 CC FA FF FF 8B D8 53 A1 00 57 00 10 50 E8 FE FA FF FF 8B F8 53 A1 00 57 00 10 50 E8 C8 FA FF FF 8B D8 53 E8 C8 FA FF FF 8B F0 85 F6 74 26 8B D7 4A B8 14 57 00 10 E8 AD F6 FF FF B8 14 57 00 10 E8 9B F6 FF FF 8B CF 8B D6 E8 DA FA FF FF 53 E8 84 FA FF FF 8D 4D EC BA F8 3A 00 10 A1 14 57 00 10 E8 0A FB FF FF 8B 55 EC B8 14 57 00 10 E8 65 F5 FF FF B8 14 57 00 10 E8 63 F6 FF FF E8 52 FC FF FF 33 C0 5A 59 59 64 89 10 68 DB 3A 00 10 8D 45 EC E8 ED F4 FF FF C3 E9 83 EF FF FF EB F0 5F 5E 5B E8 ED F3 FF FF 00 53 45 54 54 49 4E 47 53 00 00 00 00 FF FF FF FF 12 00 00 00 6B 75 74 68 37 36 67 62 62 67 36 37 34 76 38 38 67 79 }

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 4 specific false positive scenarios for the SexeCrypter11bysantasdad detection rule, along with recommended filters and exclusions tailored for a legitimate enterprise environment:

• Scenario: Endpoint Antivirus Scheduled Scans (CrowdStrike/Falcon)

  • Context: The YARA rule may detect the scanning engine’s temporary extraction of encrypted archives or heuristic analysis modules as suspicious behavior. Specifically, when CrowdStrike Falcon or Microsoft Defender runs its “On-Demand Scan” or “Deep Scan” on user document folders containing .zip or .7z files with embedded encryption headers.
  • Filter/Exclusion: Create an exclusion based on the process name and parent process. Exclude alerts where Process Name matches C-Drive.exe, FalconSensorService.exe, or MsMpEng.exe AND Parent Process is a known service host (e.g., svchost.exe). Additionally, filter out events occurring during the defined maintenance window (e.g., 02:00–04:00 UTC) where these scans are scheduled.

• Scenario: Backup Agent Operations (Veeam or Rubrik)

  • Context: Enterprise backup agents often utilize proprietary encryption algorithms to compress and secure data before transmission to the repository. The SexeCrypter11bysantasdad signature might trigger when Veeam Transport Service or Rubrik Agent processes generate temporary encrypted staging files in the %TEMP% directory, mimicking ransomware file locking behavior.
  • Filter/Exclusion: Implement a path-based exclusion for directories known to be used by backup agents (e.g., C:\ProgramData\Veeam\Backup\, C:\Rubrik\Staging). Furthermore, add a filter where the User Account is a dedicated service account (e.g., `svc-veeam-back