RAZOR1911encruptor

Hunt Hypothesis

This rule detects the presence of the RAZOR1911 encryption payload, which adversaries may deploy to obfuscate malicious code or encrypt data during post-compromise activities. Proactively hunting for this signature in Azure Sentinel allows the SOC team to identify low-severity threats that could serve as precursors to ransomware attacks or data exfiltration before they escalate to higher-impact incidents.

YARA Rule

rule RAZOR1911encruptor
{
      meta:
		author="malware-lu"
strings:
		$a0 = { E8 [2] BF [2] 3B FC 72 ?? B4 4C CD 21 BE [2] B9 [2] FD F3 A5 FC }

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 security team or IT administrator runs a YARA scanner (e.g., YARA-N, ClamAV with YARA support, or a custom Python script using yara-python) against a large directory of application binaries or logs to verify the presence of known encryption routines or specific code patterns. The scanner loads the rule file into memory, and the rule name RAZOR1911encruptor appears in the process command line or loaded module list.

  • Filter/Exclusion: Exclude processes where the parent process is a known scanner binary (e.g., yara.exe, python.exe running a scanning script) or where the command line contains arguments like -r, --rules, or paths ending in .yar/.yara.

• Scenario: A developer or DevOps engineer is debugging a custom encryption module or testing a new build of an application that embeds the RAZOR1911encruptor logic or references it in its binary strings. They run the application locally or in a CI/CD pipeline agent, and the rule name is visible in the process’s loaded DLLs or string table.

  • Filter/Exclusion: Exclude processes originating from development environments (e.g., paths containing \dev\, \build\, \ci\) or where the parent process is a build tool (e.g., msbuild.exe, dotnet.exe, npm.exe, make.exe).

• Scenario: An endpoint detection and response (EDR) agent or a security monitoring tool (e.g., CrowdStrike Falcon, Microsoft Defender for Endpoint) performs a real-time scan or on-demand scan using YARA rules. The agent loads the RAZOR1911encruptor rule into its scanning engine, and the rule name appears in the agent’s internal process state or log files,