Chinese Hacktool Set - file debug.exe

Hunt Hypothesis

This detection identifies the execution of debug.exe, a known artifact associated with Chinese hacktool sets that adversaries often leverage for initial reconnaissance and command-and-control operations. Proactively hunting for this behavior in Azure Sentinel is critical to uncover early-stage lateral movement or persistence mechanisms, even at low severity, before they escalate into more significant compromises within the cloud environment.

YARA Rule

rule FreeVersion_debug {
	meta:
		description = "Chinese Hacktool Set - file debug.exe"
		author = "Florian Roth"
		reference = "http://tools.zjqhr.com/"
		date = "2015-06-13"
		hash = "d11e6c6f675b3be86e37e50184dadf0081506a89"
	strings:
		$s0 = "c:\\Documents and Settings\\Administrator\\" fullword ascii
		$s1 = "Got WMI process Pid: %d" ascii
		$s2 = "This exploit will execute" ascii
		$s6 = "Found token %s " ascii
		$s7 = "Running reverse shell" ascii
		$s10 = "wmiprvse.exe" fullword ascii
		$s12 = "SELECT * FROM IIsWebInfo" fullword ascii
	condition:
		uint16(0) == 0x5a4d and filesize < 820KB and 3 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 7 string patterns in its detection logic.

References

• http://tools.zjqhr.com/
• Source Rule

False Positive Guidance

Here are 4 specific false positive scenarios for the Chinese Hacktool Set - file debug.exe detection rule, tailored for an enterprise environment:

• Microsoft Visual Studio Build & Debug Sessions

  • Scenario: Developers frequently compile and run applications using Microsoft Visual Studio (versions 2019–2024). The IDE spawns debug.exe processes within the installation directory (C:\Program Files\Microsoft Visual Studio\...) to attach debuggers, manage breakpoints, and inspect memory during active development cycles.
  • Suggested Filter: Exclude debug.exe instances where the file path contains \Microsoft Visual Studio\ AND the parent process is devenv.exe.

• Windows Update Troubleshooting & Diagnostics

  • Scenario: The Windows Update service or the “Windows Diagnostic Data” tool may launch a native utility named debug.exe to analyze update failures, collect telemetry logs, or troubleshoot installation errors. This often occurs during off-hours maintenance windows on domain-joined workstations and servers.
  • Suggested Filter: Exclude debug.exe located in the %WINDIR%\System32\ directory when the parent process is svchost.exe (specifically with service names like wuauserv or DiagTrack) OR when the hash matches a known Microsoft-signed binary.

• Automated CI/CD Pipeline Execution

  • Scenario: Build servers running Jenkins, GitLab Runners, or Azure DevOps agents execute automated scripts that invoke custom build tools named debug.exe. These jobs often run as scheduled tasks (e.g., nightly builds) under the context of a dedicated service account (e.g., svc-build-agent) to validate code changes before deployment.
  • Suggested Filter: Exclude debug.exe processes where the User Account is a known Service Principal