www.smorgasbordet.com/pellesc

Hunt Hypothesis

This rule detects potential web shell activity or unauthorized script execution associated with the Pelles C compiler, which adversaries may leverage to establish a foothold or execute arbitrary code on internet-facing assets. Proactively hunting for this specific URL pattern allows the SOC team to identify low-severity intrusion attempts or staging activities that might otherwise go unnoticed in Azure Sentinel before they escalate into more significant compromise.

YARA Rule

rule PellesC : Pelle Orinius
{
	meta:
		author = "_pusher_"
		date = "2016-08"
		description = "www.smorgasbordet.com/pellesc"
	strings:		
		$aa0 = " -- terminating\x0D\x0A\x00 -- terminating\x0A\x00CRT: \x00unexpected error\x00" wide ascii nocase	
		$aa1 = "unhandled exception (main)\x00unhandled exception in thread\x00unable to create thread\x00unable to destroy semaphore\x00" wide ascii nocase
		$aa2 = "unable to wait on semaphore\x00unable to post semaphore\x00unable to init semaphore\x00unable to unlock mutex\x00unable to lock mutex\x00unable to init mutex\x00" wide ascii nocase
		$aa3 = "invalid stream lock number\x00corrupt per-thread data\x00out of memory\x00unable to init threads\x00unable to init HEAP" wide ascii nocase
	condition:
		3 of ($aa*) and
		(pe.linker_version.major == 2) and (pe.linker_version.minor == 50 )
}

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 4 string patterns in its detection logic.

• Source Rule

False Positive Guidance

• Developer Build Automation and CI/CD Pipelines

  • Scenario: In a software development environment, build agents (e.g., Jenkins, Azure DevOps, or GitHub Actions) may download the Pelles C compiler or its documentation/source code from www.smorgasbordet.com/pellesc during a nightly build job or when a developer manually triggers a dependency update for a C-language project. This is a legitimate retrieval of a known, albeit niche, development tool.
  • Filter/Exclusion: Exclude network connections where the source IP belongs to the designated CI/CD subnet or where the process name matches common build agents (e.g., java.exe, node.exe, python.exe, jenkins-agent.exe) and the destination URL contains /pellesc.

• Legacy Application Maintenance and Patching

  • Scenario: An IT operations team is maintaining a legacy internal application that relies on a specific version of the Pelles C runtime or headers. A scheduled PowerShell script or a manual admin action downloads the compiler package or updates the local cache of the tool from the official site to ensure compatibility with new build environments.
  • Filter/Exclusion: Create an exclusion for processes initiated by service accounts (e.g., svc-legacy-app, admin-maintenance) or for scheduled tasks named LegacyAppUpdate or CompilerCacheRefresh that connect to www.smorgasbordet.com.

• Technical Documentation and Knowledge Base Caching

  • Scenario: A corporate wiki or internal knowledge base system (e.g., Confluence, SharePoint, or a custom internal portal) uses a web crawler or document sync service to archive or reference technical documentation for the Pelles C compiler. The crawler fetches the landing page or specific documentation files from www.smorgasbordet.com/pellesc to keep the internal copy up-to