This detection identifies potential adversary activity involving the use of the Pelles C 4.50 x86 CRT library DLL, which may indicate the execution of custom or obfuscated tools designed to evade standard signature-based defenses. SOC teams should proactively hunt for this indicator in Azure Sentinel to uncover stealthy lateral movement or initial access attempts that leverage less common development libraries often overlooked by baseline monitoring.
rule PellesC450DLLX86CRTLIB
{
meta:
author="malware-lu"
strings:
$a0 = { 55 89 E5 53 56 57 8B 5D 0C 8B 75 10 85 DB 75 0D 83 3D [4] 00 75 04 31 C0 EB 57 83 FB 01 74 05 83 FB 02 75 }
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.
Here are 3-5 specific false positive scenarios for the PellesC450DLLX86CRTLIB detection rule, along with recommended filters and exclusions:
Scenario: Deployment of Pelles C Compiler Toolchains on Build Servers
msvcrt.dll and related CRT libraries which match the YARA signature.C:\Program Files\Pelles C\lib\crt\) or exclude file hashes known to be part of the official installer package during scheduled maintenance windows.Scenario: Execution of Legacy Engineering Simulation Software
SimEngine.exe, CadPluginLoader.exe) running under specific service accounts (e.g., DOMAIN\ENG-SVC-01).Scenario: Scheduled Backup of Development Repositories