RECryptv07xCruddRETh2

Hunt Hypothesis

This YARA rule targets specific cryptographic or obfuscated code patterns, likely indicating the presence of a low-severity malware variant or a custom encryption routine used by an adversary to hide malicious payloads. Proactively hunting for these signatures in Azure Sentinel allows the SOC to identify early-stage infections or dormant backdoors that may not yet trigger high-fidelity alerts, reducing the window of opportunity for lateral movement or data exfiltration.

YARA Rule

rule RECryptv07xCruddRETh2
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 60 E8 00 00 00 00 5D 55 81 04 24 0A 00 00 00 C3 8B F5 81 C5 [2] 00 00 89 6D 34 89 75 38 8B 7D 38 81 E7 00 FF FF FF 81 C7 48 00 00 00 47 03 7D 60 8B 4D 5C 83 F9 00 7E 0F 8B 17 33 55 58 89 17 83 C7 04 83 C1 FC EB EC 8B }

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

• Antivirus Signature Update (Microsoft Defender for Endpoint): When the endpoint agent performs a scheduled definition update, the MpSigStub.exe or MpClient.exe process may temporarily load or write encrypted signature files to disk, potentially matching the RECryptv07xCruddRETh2 YARA pattern if it targets specific cryptographic header structures.
  • Filter/Exclusion: Exclude processes named MpSigStub.exe, MpClient.exe, or MsMpEng.exe from the detection scope, or filter out file paths under C:\ProgramData\Microsoft\Windows Defender\.
• SQL Server Full-Text Index Rebuild: During a scheduled maintenance window, the SQL Server service (sqlservr.exe) may generate temporary encrypted or compressed index files in the tempdb or user database directories. If the YARA rule matches specific byte sequences in these binary index structures, it can trigger on legitimate database maintenance tasks.
  • Filter/Exclusion: Exclude file paths containing \MSSQL\ or \SQLServer\ and processes named sqlservr.exe or sqlagent.exe from the alerting logic.
• Adobe Creative Cloud Auto-Update: The Adobe Creative Cloud desktop app (CCXProcess.exe or AdobeUpdate.exe) frequently downloads and installs encrypted update packages to the user’s AppData folder. These packages often use proprietary encryption schemes that may inadvertently match the RECryptv07xCruddRETh2 pattern if the rule is not strictly specific to malware families.
  • Filter/Exclusion: Exclude file paths under C:\Users\<User>\AppData\Local\Adobe\ and processes named CCXProcess.exe, AdobeUpdate.exe, or AdobeGenuineSoftwareInstaller.exe.
• VMware Workstation Snapshot Creation: When an administrator creates a snapshot of