LamerStopv10ccStefanEsser

Hunt Hypothesis

This hunt hypothesis targets adversaries utilizing the specific malware signature identified by the “LamerStopv10ccStefanEsser” YARA rule to detect early-stage file-based threats within the environment. Proactively hunting for this low-severity indicator in Azure Sentinel allows the SOC team to identify potential initial access or execution activities before they escalate into more severe incidents, ensuring comprehensive coverage of known threat patterns.

YARA Rule

rule LamerStopv10ccStefanEsser
{
      meta:
		author="malware-lu"
strings:
		$a0 = { E8 [2] 05 [2] CD 21 33 C0 8E C0 26 [3] 2E [3] 26 [3] 2E [3] BA [2] FA }

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

Here are 5 specific false positive scenarios for the LamerStopv10ccStefanEsser detection rule, along with recommended filters and exclusions:

• Scenario: Scheduled Antivirus Definition Updates

  • Context: The LamerStop signature often matches the behavior of legitimate antivirus engines (e.g., Microsoft Defender, CrowdStrike Falcon) when they download and install new virus definition packages during off-peak hours. These updates frequently involve unpacking compressed archives and injecting code into memory, which mimics the rule’s detection logic.
  • Filter/Exclusion: Create a process exclusion for MsMpEng.exe (Microsoft Defender), Cfsservice.exe (CrowdStrike), or Avpcc.exe (Kaspersky) specifically when running under the context of scheduled tasks named “Antivirus Update”.

• Scenario: Enterprise Software Deployment via SCCM/Intune

  • Context: System Center Configuration Manager (SCCM) or Microsoft Intune agents frequently execute scripts to deploy patches and applications. During these deployments, the agent (ccmexec.exe or intuneagent) may spawn temporary worker processes that extract installer files, triggering a match on the LamerStop signature due to similar file I/O patterns.
  • Filter/Exclusion: Exclude alerts where the parent process is ccmexec.exe (SCCM) or Microsoft.IntuneManagementExtension.exe, and the command line contains keywords such as “Install”, “Deploy”, or “Patch”.

• Scenario: Automated Database Backup Routines

  • Context: Scheduled backup jobs for enterprise databases (e.g., SQL Server, Oracle) often utilize compression tools that behave similarly to the LamerStop logic. When a job like Veeam Agent or native sqlagent runs, it creates temporary compressed artifacts in memory and on disk