BopCryptv10

Hunt Hypothesis

This rule targets the execution of BopCrypt ransomware variants, indicating an adversary has deployed a known crypto-ransomware payload to encrypt files and disrupt operations. Proactively hunting for this signature allows the SOC to identify early-stage infections or dormant payloads before the encryption process begins, reducing the potential impact on Azure-hosted workloads.

YARA Rule

rule BopCryptv10
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 60 BD [4] E8 [2] 00 00 }

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

• Legacy Application Deployment via Group Policy: Administrators deploying older, unpatched enterprise applications (e.g., specific versions of legacy ERP or CAD software) that were compiled with older Borland/C++ toolchains may contain static strings or byte patterns matching the BopCryptv10 signature.
  • Filter/Exclusion: Exclude file paths under standard application directories (e.g., C:\Program Files\LegacyApp\) or specific executable names (e.g., LegacyApp.exe) if confirmed as known-good binaries via hash verification.
• Scheduled Backup Job Execution: Enterprise backup solutions (e.g., Veeam, Commvault, or Windows Server Backup) often execute helper executables or agent binaries in temporary or service directories. If these binaries are statically linked with older C++ libraries, they may trigger the YARA rule during routine scheduled backups (e.g., daily at 02:00 AM).
  • Filter/Exclusion: Exclude processes spawned by known backup service accounts (e.g., svc-backup) or file paths containing backup, agent, or helper in the directory structure, provided the parent process is a verified backup service.
• Development Environment Compilation Artifacts: Developers using older IDEs (e.g., Borland C++ Builder 5/6 or early Visual C++ 6.0) may leave compiled debug binaries or test executables in shared network drives or local user profiles. These artifacts, especially if copied to shared locations for code review, can match the BopCryptv10 signature due to embedded library strings.
  • Filter/Exclusion: Exclude files located in user-specific development directories (e.g., C:\Users\<dev_user>\Projects\ or \\fileserver\dev\builds\) or files with extensions like .pdb or .obj if the rule is