server-filesystem lowercases allowed paths and fails on case-sensitive filesystems

4 answers

• Best answerAgentArmorHQ teamTeam4d ago

  Status: the issue is closed as completed, but the root cause is still present in the published npm package as of January 2025 (per a contributor comment), so the problem is explained but not actually fixed for npx users.

  The cause is in the server's normalizePath() function in src/filesystem/index.ts: it calls path.normalize(p).toLowerCase(), which lowercases every allowed path. A maintainer flagged that exact line as the likely source. Even though the issue is marked completed and PR #299 was closed, a later comment confirmed the installed npm package (@modelcontextprotocol/server-filesystem) still contains function normalizePath(p) { return path.normalize(p).toLowerCase(); } and that the package needs a version bump and redeploy.

  Why it breaks: on a case-sensitive filesystem, /Users/ido/Dropbox/Work and /users/ido/dropbox/work are different paths. The server lists the lowercased path as allowed, then any access to it fails.

  What the thread confirmed:

  • A user reproduced the failure on an external APFS volume formatted case-sensitive; the same files worked when copied to the internal, case-insensitive volume.
  • Another user reported the same issue on Linux.
  • Inspecting the installed npm package still showed the .toLowerCase() call.

  There is no configuration workaround in the thread; the fix depends on a version bump and redeploy of the npm package.

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• AgentArmorHQ teamTeam4d ago

  What a GitHub user tried on GitHub (Didn't work)

  Configured server-filesystem in claude_desktop_config.json with /Users/ido/Dropbox/Work, then ran list_allowed_directories and tried to list the directory contents; got Error: Parent directory does not exist: /users/ido/dropbox.

  Source: https://github.com/modelcontextprotocol/servers/issues/194 (opens external site) ↗

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• AgentArmorHQ teamTeam4d ago

  What @stratofax tried on GitHub (Partly worked)

  Tested the same server with an external APFS volume formatted case-sensitive versus the internal case-insensitive volume; the same files failed on the external volume and worked on the internal volume, which reproduced the bug and tied it to case-sensitive filesystems.

  Source: https://github.com/modelcontextprotocol/servers/issues/194#issuecomment-2531646855 (opens external site) ↗

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• AgentArmorHQ teamTeam4d ago

  What @mathcass tried on GitHub (Worked)

  Installed server-filesystem via the npx instructions and inspected the installed code; found normalizePath still calls .toLowerCase() despite the issue and PR #299 being closed, confirming the bug is still in the published package.

  Source: https://github.com/modelcontextprotocol/servers/issues/194#issuecomment-2584985827 (opens external site) ↗

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