CHECKPRGc1992

Hunt Hypothesis

This YARA rule targets the specific binary signature of the CHECKPRGc1992 malware, which is often associated with legacy or low-level system components that adversaries may leverage for persistence or initial access. Proactively hunting for this signature in Azure Sentinel allows the SOC team to identify dormant or overlooked instances of this low-severity threat within the environment before it can be chained with other tactics to escalate privileges or exfiltrate data.

YARA Rule

rule CHECKPRGc1992
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 33 C0 BE [2] 8B D8 B9 [2] BF [2] BA [2] 47 4A 74 }

condition:
		$a0 at pe.entry_point
}

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 1 string patterns in its detection logic.

• Source Rule

False Positive Guidance

• Legacy Application Installer Execution: The CHECKPRGc1992 YARA rule likely targets specific byte patterns or strings associated with older, proprietary check programs or configuration utilities (e.g., checkprg.exe or similar) that are part of legacy enterprise software stacks. These executables are often invoked by legacy application installers or maintenance scripts during patching cycles.

  • Filter/Exclusion: Exclude processes where the parent process is a known installer (e.g., msiexec.exe, setup.exe, install.exe) and the file path resides in a standard legacy application directory (e.g., C:\Program Files\LegacyApp\bin\).

• Scheduled Health Check Jobs: Enterprise environments often use scheduled tasks (via schtasks.exe or Task Scheduler) to run periodic health check or integrity verification scripts. These jobs may execute a binary named checkprg or similar to validate service states or configuration files, triggering the YARA match if the rule inspects the binary header or specific function names.

  • Filter/Exclusion: Exclude events where the command line contains arguments typical of health checks (e.g., /verify, /status, /check) and the process is launched by svchost.exe or taskschd.exe with a known service name (e.g., HealthCheckService).

• Third-Party Monitoring Agent Components: Some APM (Application Performance Monitoring) or endpoint monitoring agents (e.g., Dynatrace, AppDynamics, or custom internal tools) include helper binaries for log collection or state checking that may share naming conventions or code structures with the target of CHECKPRGc1992. These agents run continuously and may be restarted by service control managers.

  • Filter/Exclusion: Exclude processes whose parent is a known monitoring agent service (e.g., `dynat