The detection rule identifies potential malicious activity involving the msvcrt_WIN8AMD64 YARA signature, which may indicate the presence of obfuscated or custom malware leveraging Windows runtime libraries. SOC teams should proactively hunt for this behavior in Azure Sentinel to identify and mitigate advanced threats that may evade traditional detection methods.
YARA Rule
rule msvcrt_WIN8AMD64 {
meta:
author = "Jaume Martin"
condition:
hash.md5(0, filesize) == "33c59fcdf027470e0ab1d366f54a6ebf"
}
This YARA rule can be deployed in the following contexts:
Scenario: Microsoft Windows Update Installer
Description: The Windows Update installer may use components from msvcrt.dll which is part of the msvcrt_WIN8AMD64 YARA rule.
Filter/Exclusion: Check for the presence of WindowsUpdate.exe or wusa.exe in the process tree or file path.
Scenario: Microsoft .NET Framework Installation
Description: Installing or repairing the .NET Framework can involve loading msvcrt.dll as part of the installation process.
Filter/Exclusion: Filter by file paths containing dotnetfx or netfx in the full path.
Scenario: Scheduled Task Running a Legacy Application
Description: A scheduled task may run a legacy application that dynamically loads msvcrt.dll for compatibility.
Filter/Exclusion: Exclude processes with Task Scheduler as the parent process or filter by known legacy application names (e.g., LegacyApp.exe).
Scenario: Microsoft SQL Server Service
Description: SQL Server services may use msvcrt.dll as part of its runtime dependencies on Windows 8 AMD64 systems.
Filter/Exclusion: Filter by process names such as sqlservr.exe or check for the presence of SQL Server service identifiers.
Scenario: Microsoft Visual C++ Redistributable Installation
Description: Installing or updating the Microsoft Visual C++ Redistributable package may trigger the rule due to msvcrt.dll usage.
Filter/Exclusion: Check for file paths containing vcredist.exe or VC_redist.exe in the command line or file system.