RECryptv07xCruddRETh1

Hunt Hypothesis

This YARA rule targets the specific RECryptv07xCruddRETh1 signature, likely indicating the presence of a custom or obfuscated cryptor used to hide malicious payloads or ransomware components within memory or on disk. Proactively hunting for this signature allows the SOC team to identify stealthy encryption activities that may precede data exfiltration or ransom deployment, enabling early intervention before the adversary achieves full compromise.

YARA Rule

rule RECryptv07xCruddRETh1
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 60 E8 00 00 00 00 5D 81 ED F3 1D 40 00 B9 7B 09 00 00 8D BD 3B 1E 40 00 8B F7 61 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 }

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

• Scenario: A DevOps engineer runs a custom Python script to encrypt sensitive configuration files (e.g., secrets.json) using the cryptography library before committing them to a Git repository. The script imports the Crypto.Cipher.AES module, which matches the YARA pattern for AES encryption routines.

  • Filter/Exclusion: Exclude processes where the parent process is python.exe or python3.exe and the command line contains arguments like encrypt, cipher, or aes. Alternatively, exclude files located in specific development directories like C:\dev\projects\ or D:\src\.

• Scenario: The enterprise backup solution (e.g., Veeam, Commvault, or Acronis) performs a scheduled nightly backup job. The backup agent service (vssadmin.exe or commvaultagent.exe) uses AES-256 encryption to write backup blocks to the storage target, triggering the detection on the service process.

  • Filter/Exclusion: Exclude known backup service executables such as vssadmin.exe, commvaultagent.exe, acronisbackup.exe, or veritasbackup.exe. Additionally, exclude processes running under the SYSTEM or BackupService account names.

• Scenario: An IT administrator uses a legitimate disk encryption tool like BitLocker (via manage-bde.exe) or a third-party tool like Symantec PGP to encrypt a new hard drive or partition. The encryption driver or user-mode helper process invokes cryptographic primitives that match the YARA rule.

  • Filter/Exclusion: Exclude processes named manage-bde.exe, bitlockersetup.exe, pgp.exe, or pgpagent.exe. Also, consider excluding processes that are child processes of services.exe or svchost.exe when the service name corresponds to