Anti-Sandbox checks for CWSandbox

Hunt Hypothesis

Adversaries may execute anti-sandbox checks to evade detection in sandboxed environments, indicating potential malicious behavior. SOC teams should proactively hunt for these checks in Azure Sentinel to identify and mitigate threats that bypass automated analysis tools.

YARA Rule

rule antisb_cwsandbox {
    meta:
        author = "x0r"
        description = "Anti-Sandbox checks for CWSandbox"
	version = "0.1"
    strings:
        $p1 = "Software\\Microsoft\\Windows\\CurrentVersion" nocase
        $s1 = "76487-644-3177037-23510"
    condition:
        all of them
}

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 2 string patterns in its detection logic.

• Source Rule

False Positive Guidance

• Scenario: Scheduled System Maintenance Task
  Description: A legitimate scheduled task runs a system cleanup or disk defragmentation tool that temporarily modifies system files or processes.
  Filter/Exclusion: process.name != "defrag.exe" AND process.name != "cleanmgr.exe"

• Scenario: Windows Defender Scan
  Description: Windows Defender performs a full system scan, which may trigger anti-sandbox checks due to file access or process creation.
  Filter/Exclusion: process.name != "WindowsDefender.exe" AND process.name != "MsMpEng.exe"

• Scenario: Admin Task - Group Policy Update
  Description: An administrator runs a Group Policy update (gpupdate /force) which may cause system-wide changes that mimic sandbox behavior.
  Filter/Exclusion: process.name != "gpupdate.exe"

• Scenario: Log Collection and Analysis Tool
  Description: A tool like Splunk or ELK Stack is collecting logs and may interact with system processes or files in a way that triggers the rule.
  Filter/Exclusion: process.name != "splunkd.exe" AND process.name != "logstash.exe"

• Scenario: Virtualization Tools in Development Environment
  Description: A developer is using VMware or VirtualBox to run a test environment, which may cause sandbox-like process behavior.
  Filter/Exclusion: process.name != "vmtoolsd.exe" AND process.name != "VBoxTray.exe"