The 'MCP Filesystem Server Suspicious Extension Write' detection rule identifies potentially malicious activities by monitoring attempts to create executable or script files through MCP filesystem server connections. This is particularly relevant given the rise of advanced threat actors using LLM-based tools to generate and deploy malicious scripts for persistence or execution on targeted systems. The rule focuses on detecting writes to sensitive directories, such as system or startup paths, where the presence of executable files could signify malicious intent. The detection logic employs Splunk's search capabilities to analyze file write events and checks for specific file extensions typically associated with scripts or executables. It highlights the importance of monitoring user behaviors and system interactions with files that could have harmful repercussions if executed. The rule aims to minimize false positives by considering legitimate use cases while prioritizing indicators of possible compromise.