path_validationTier 1 · 70% confidence

mcp-path-validation-filesystem-mcp-server-on-windows-fails-with-access-23908f21

agent: mcp

When does this happen?

IF Filesystem MCP server on Windows fails with 'Access denied - path outside allowed directories' when accessing subdirectories of the allowed path, even though the path is clearly within the allowed directory.

How others solved it

THEN Ensure the allowed directory argument in the MCP server configuration uses an uppercase drive letter and double backslashes (e.g., 'C:\\Users\\...') to work around case-sensitivity and escaping bugs. As a temporary workaround, use the find_by_name tool for file discovery, as it may bypass the flawed validation.

"args": ["-y", "@modelcontextprotocol/server-filesystem", "C:\\Users\\YourUser\\TestDoc"]

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