Look for DCP RijnDael Init

Hunt Hypothesis

The DCP RijnDael Init rule detects the initial execution of a potential ransomware payload, indicating an adversary may be establishing a foothold in the environment. SOC teams should proactively hunt for this behavior to identify early-stage ransomware activity and prevent data exfiltration or encryption before it escalates.

YARA Rule

rule DCP_RIJNDAEL_Init {
	meta:
		author = "_pusher_"
		description = "Look for DCP RijnDael Init"
		date = "2016-07"
	strings:
		$c0 = { 55 8B EC 51 53 56 57 89 4D FC 8B FA 8B D8 8B 75 08 56 8B D7 8B 4D FC 8B C3 E8 ?? ?? ?? ?? 8B D7 8B 4D FC 8B C3 8B 38 FF 57 ?? 85 F6 75 25 8D 43 38 33 C9 BA 10 00 00 00 E8 ?? ?? ?? ?? 8D 4B 38 8D 53 38 8B C3 8B 30 FF 56 ?? 8B C3 8B 10 FF 52 ?? EB 16 8D 53 38 8B C6 B9 10 00 00 00 E8 ?? ?? ?? ?? 8B C3 8B 10 FF 52 ?? 5F 5E 5B 59 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 Maintenance Task
  Description: A legitimate scheduled task runs a maintenance script that temporarily uses the DCP RijnDael Init command as part of a system cleanup or update process.
  Filter/Exclusion: Exclude processes associated with known system maintenance tools (e.g., task scheduler, Windows Update, SCCM), or filter by process name like schtasks.exe or wuauclt.exe.

• Scenario: Database Backup Job
  Description: A database backup tool (e.g., SQL Server Backup, MySQL Backup) initiates a backup operation that includes the DCP RijnDael Init command as part of its initialization phase.
  Filter/Exclusion: Exclude processes related to database backup tools (e.g., sqlbackup.exe, mysqldump.exe) or filter by the presence of known backup directories or log files.

• Scenario: Network Configuration Change
  Description: An administrator manually configures a network interface or updates routing tables, which may trigger the DCP RijnDael Init command as part of a network management tool (e.g., Cisco IOS, Windows Network Adapter Settings).
  Filter/Exclusion: Exclude processes initiated by network configuration tools (e.g., netsh.exe, ipconfig.exe) or filter by user context (e.g., Administrator or Network Admin).

• Scenario: Application Initialization During Deployment
  Description: A software deployment tool (e.g., Chocolatey, Ansible, Puppet) runs a script that initializes a component using the DCP RijnDael Init command during application installation or configuration.
  Filter/Exclusion: Exclude processes associated with deployment tools (e.g., choco.exe, ansible.exe, puppet.exe) or filter by