EXERefactorV01random

Hunt Hypothesis

This detection identifies potential malware or suspicious executables that utilize randomization in their file structure to evade static analysis and signature-based defenses. Proactively hunting for this behavior in Azure Sentinel allows the SOC team to uncover stealthy threats that may bypass standard AV solutions by analyzing YARA rule matches across endpoint telemetry before an incident escalates.

YARA Rule

rule EXERefactorV01random
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 55 8B EC 81 EC 90 0B 00 00 53 56 57 E9 58 8C 01 00 55 53 43 41 54 49 4F 4E }

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

Here are 4 specific false positive scenarios for the EXERefactorV01random detection rule, including suggested filters and exclusions:

• Scenario: Automated Build Pipeline Execution

  • Context: CI/CD platforms like Jenkins, GitLab Runner, or Azure DevOps Agents frequently compile source code into new .exe binaries during the build phase. These agents often generate temporary executables with randomized naming conventions (e.g., build_8f3a2.exe) in staging directories, which mimics the “random” behavior targeted by the rule.
  • Filter/Exclusion: Exclude processes spawned by known CI service accounts (e.g., JenkinsService, GitLabRunner) and restrict detection to paths outside of build artifact folders such as C:\Builds\Staging or /var/lib/jenkins/workspace.

• Scenario: Endpoint Security Self-Defense Scans

  • Context: Antivirus solutions like CrowdStrike Falcon, SentinelOne, or Microsoft Defender for Endpoint periodically extract and execute sandboxed versions of monitored files to perform heuristic analysis. These tools often create temporary executable instances with randomized hashes in their quarantine or sandbox directories (C:\ProgramData\CrowdStrike\), triggering the rule when they refactor internal components.
  • Filter/Exclusion: Create a whitelist for processes running under the service accounts of major EDR vendors (e.g., CrowdStrike Falcon Sensor, SentinelOne Agent) and exclude file paths containing keywords like Sandbox, Quarantine, or Temp.

• Scenario: Scheduled Software Deployment via Configuration Management

  • Context: Enterprise configuration tools such as Microsoft SCCM (Configuration Manager), Ansible, or Puppet execute scheduled deployment jobs that install or update software. These agents often generate