This hunt targets adversaries deploying the VNCLink.exe remote access tool to establish persistent command and control channels within Azure Sentinel environments. Proactive investigation is essential because this specific Chinese hacktool may be leveraged for stealthy data exfiltration or lateral movement that standard low-severity alerts might overlook without deeper behavioral analysis.
rule CN_Tools_VNCLink {
meta:
description = "Chinese Hacktool Set - file VNCLink.exe"
author = "Florian Roth"
reference = "http://tools.zjqhr.com/"
date = "2015-06-13"
hash = "cafb531822cbc0cfebbea864489eebba48081aa1"
strings:
$s1 = "C:\\temp\\vncviewer4.log" fullword ascii
$s2 = "[BL4CK] Patched by redsand || http://blacksecurity.org" fullword ascii
$s3 = "fake release extendedVkey 0x%x, keysym 0x%x" fullword ascii
condition:
uint16(0) == 0x5a4d and filesize < 580KB and 2 of them
}
This YARA rule can be deployed in the following contexts:
This rule contains 3 string patterns in its detection logic.
Here are 4 specific false positive scenarios for the Chinese Hacktool Set - file VNCLink.exe detection rule in an enterprise environment:
Remote Desktop Administration via Citrix or VMware Horizon
VNCLink.exe as a native component of remote desktop gateways (specifically within Citrix Workspace or VMware Horizon Client) to establish secure connections between the endpoint and the virtual desktop infrastructure. This file is often launched by the user’s daily login routine rather than malicious activity.VNCLink.exe when the parent process is CitrixWorkspaceApp.exe, HorizonClient.exe, or svchost.exe (specifically the “Remote Desktop Services” service), and restrict this to known administrative user groups (e.g., Domain Admins).Scheduled Patch Management Deployment
VNCLink.exe in its deployment package to facilitate remote session handshakes during the installation of critical security updates. This triggers the rule every Tuesday at 02:00 AM when the scheduled job executes across all workstations.C:\Program Files\Ivanti\Endpoint Manager\Components\) and the execution time falls within the defined maintenance window (01:00–04:00 local time).Legacy Application Support for Financial Reporting