unc-filesystem-mcp by BlockSecCA - MCP Server

UNC Filesystem MCP

MCP server for filesystem operations with proper UNC path support on Windows.

Why?

The built-in Claude Desktop filesystem server has bugs with network paths:

Drive letter resolution is asymmetric: Mapped drives (e.g., Z:) get resolved to their UNC equivalent at config load time, but incoming requests are compared literally. Result: access denied.
UNC subdirectory matching fails: Even when \\server\share is in the allowed list, accessing \\server\share\subfolder is rejected.

This server normalizes both sides of the path comparison, so mapped drives and UNC subdirectories work correctly.

Installation

Option 1: MCPB Package (Recommended)

Download unc-filesystem-mcp.mcpb from releases
Double-click to install in Claude Desktop
Use the folder picker to add allowed directories
Restart Claude Desktop

Option 2: Manual Setup

git clone https://github.com/BlockSecCA/unc-filesystem-mcp.git
cd unc-filesystem-mcp
npm install
npm run build

Add to claude_desktop_config.json:

{
  "mcpServers": {
    "unc-fs": {
      "command": "node",
      "args": [
        "C:/path/to/unc-filesystem-mcp/dist/index.js",
        "\\\\server\\share",
        "Z:\\",
        "C:\\Users\\Me\\Documents"
      ]
    }
  }
}

Tools

Tool	Description
`read_file`	Read file contents with optional `head`/`tail` line limits
`write_file`	Create or overwrite files
`edit_file`	Replace unique text in file, returns unified diff
`list_directory`	List directory contents with `[FILE]`/`[DIR]` prefixes
`search_files`	Recursive glob-based file search
`get_file_info`	File/directory metadata (size, dates, permissions)
`list_allowed_directories`	Show configured allowed paths

Building from Source

npm install
npm run build          # Compile TypeScript
npm run pack           # Create .mcpb package (requires @anthropic-ai/mcpb)

How It Works

The fix is in path normalization. Both the configured allowed directories and incoming request paths are normalized to the same format before comparison:

Backslashes → forward slashes
Lowercase for case-insensitive matching
UNC paths preserved as-is
Local paths resolved to absolute

This ensures Z:\subfolder matches against //server/share/ when Z: is mapped to \\server\share.

License

MIT - Carlos - BlockSecCA