Look for DCP Blowfish EncryptCBC

Hunt Hypothesis

The hypothesis is that the detection rule identifies potential encryption activity using the DCP Blowfish EncryptCBC method, which may indicate data exfiltration or obfuscation efforts by an adversary. SOC teams should proactively hunt for this behavior in Azure Sentinel to identify and mitigate potential data manipulation or stealthy communication tactics.

YARA Rule

rule DCP_BLOWFISH_EncryptCBC {
	meta:
		author = "_pusher_"
		description = "Look for DCP Blowfish EncryptCBC"
		date = "2016-07"
	strings:
		$c0 = { 55 8B EC 83 C4 F0 53 56 57 89 4D F8 89 55 FC 8B D8 80 7B 34 00 75 16 B9 ?? ?? ?? ?? B2 01 A1 ?? ?? ?? ?? E8 ?? ?? ?? ?? E8 ?? ?? ?? ?? 8B 7D 08 85 FF 79 03 83 C7 07 C1 FF 03 85 FF 7E 56 BE 01 00 00 00 6A 08 8B 45 FC 8B D6 4A C1 E2 03 03 C2 8D 4D F0 8D 53 54 E8 ?? ?? ?? ?? 8D 4D F0 8D 55 F0 8B C3 E8 ?? ?? ?? ?? 8B 55 F8 8B C6 48 C1 E0 03 03 D0 8D 45 F0 B9 08 00 00 00 E8 ?? ?? ?? ?? 8D 53 54 8D 45 F0 B9 08 00 00 00 E8 ?? ?? ?? ?? 46 4F 75 AF 8B 75 08 81 E6 07 00 00 80 79 05 4E 83 CE F8 46 85 F6 74 26 8D 4D F0 8D 53 54 8B C3 E8 ?? ?? ?? ?? 56 8B 4D F8 03 4D 08 2B CE 8B 55 FC 03 55 08 2B D6 8D 45 F0 E8 ?? ?? ?? ?? 8D 45 F0 B9 FF 00 00 00 BA 08 00 00 00 E8 ?? ?? ?? ?? 5F 5E 5B 8B E5 5D C2 04 00 }
	condition:
		$c0
}

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: Scheduled System Backup Using DCP Blowfish EncryptCBC
  Description: A legitimate scheduled backup job uses DCP Blowfish EncryptCBC to encrypt backup files before storage.
  Filter/Exclusion: Exclude processes initiated by the backup service account (e.g., BackupService or System) during known backup windows.

• Scenario: Administrative Task to Encrypt Configuration Files
  Description: An admin manually encrypts configuration files using DCP Blowfish EncryptCBC as part of a security hardening task.
  Filter/Exclusion: Exclude processes initiated by admin accounts (e.g., Administrator or Domain Admins) with known encryption tasks in their activity logs.

• Scenario: Log File Encryption Using DCP Blowfish EncryptCBC
  Description: A log management tool encrypts log files using DCP Blowfish EncryptCBC to meet compliance requirements.
  Filter/Exclusion: Exclude processes associated with log management tools (e.g., Splunk, ELK Stack, or Logstash) and filter by known log encryption directories.

• Scenario: Automated Script for Data Migration with Encryption
  Description: A script runs during a data migration process and uses DCP Blowfish EncryptCBC to encrypt data during transfer.
  Filter/Exclusion: Exclude processes initiated by migration scripts (e.g., migration_script.exe) and filter by migration-related directories or timestamps.

• Scenario: Third-Party Application Using DCP Blowfish EncryptCBC for Data Protection
  Description: A third-party application (e.g., SecureDataVault) uses DCP Blowfish EncryptCBC to protect sensitive data at rest.
  Filter/Exclusion: Exclude processes associated with known third-party applications and filter by application-specific process names or service identifiers.