This YARA rule identifies the presence of VcasmProtector, a lightweight virtual machine-based code protector often used by threat actors to obfuscate malicious payloads and evade static analysis. Proactively hunting for this indicator in Azure Sentinel allows the SOC to uncover hidden or dormant malware components that may have been deployed on endpoints, ensuring that obfuscated threats are detected before they can execute or persist within the environment.
rule VcasmProtectorV1Xvcasm
{
meta:
author="malware-lu"
strings:
$a0 = { EB ?? 5B 56 50 72 6F 74 65 63 74 5D }
condition:
$a0 at pe.entry_point
}This YARA rule can be deployed in the following contexts:
This rule contains 1 string patterns in its detection logic.
InternalReportGenerator.exe) that has been packed or obfuscated using a custom VCASM-based protector to reduce binary size or hide logic. This is common in niche enterprise apps not built with standard frameworks like .NET or C++ standard libraries.
C:\Apps\InternalTools\) or add an exception for the specific hash of the known-good binary if it is stable across deployments.VendorBackupAgent.exe from a niche backup or monitoring solution) that uses VCASM protection to prevent reverse engineering. These tools are often signed by the vendor but may not be in the standard trusted publisher list.
C:\Program Files\VendorName\Backup\Agent\) if the vendor confirms the use of this protector.NightlyLogCompressor) runs a small, custom-written script or binary that uses VCASM to compress or protect log processing logic. This binary is executed by the Task Scheduler service (TaskScheduler.exe) and resides in a system temp or maintenance folder.
TaskScheduler.exe or svchost.exe (if the task is registered under a system service) and the file path matches the known maintenance directory (e.g., C:\Windows\Temp\Maintenance\).