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Upgrade to fastmcp 4.0.5 (fixes COR2-475 path traversal at the source) - #16
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fastmcp 4 URL-encodes OpenAPI path parameters, which removes the path-traversal vector at the source (COR2-475) rather than guarding against it. The migration is import moves only -- the OpenAPI types were relocated, not changed: MCPType and the OpenAPI component classes now live in fastmcp.server.providers.openapi, HTTPRoute in fastmcp.utilities.openapi.models. Both callback signatures are unchanged, so custom_route_mapper and customize_components keep their bodies. fastmcp 4 moves to httpx2; applications call httpx2.alias_httpx() once at startup so existing `import httpx` code shares the httpx2 classes. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01LZtC15RMphgMhtsoDh4i4u
The previous commit swapped the httpx dependency for httpx2 but left
`import httpx` in src/clients/cortex.py, working only because the
downstream application called httpx2.alias_httpx() first. That broke
cortex-mcp as a standalone package -- its own console script and
Dockerfile entry point import that module directly:
ModuleNotFoundError: No module named 'httpx'
The tests did not catch it because none of them import src.clients.cortex.
httpx2's alias_httpx() is documented for applications, not libraries, and
cortex-mcp is imported as a library by cortex-remote-mcp. Import httpx2
under the httpx name in this module instead, so the package is correct on
its own and no longer depends on import ordering elsewhere.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LZtC15RMphgMhtsoDh4i4u
The import-path migration left a line ruff's isort rule wants split; CI runs `ruff check src tests` and failed on it. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01LZtC15RMphgMhtsoDh4i4u
brucesw
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Sep 23, 2026
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LGTM! Seems pretty straightforward. Thanks for taking this on.
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Why
fastmcp 2.12.3 interpolates OpenAPI path parameters into the backend URL with a plain
str.replace, unescaped. httpx then resolves the dot-segments per RFC 3986 while building the request, so a tool argument of../../internal/usersfortagOrIdproduced a real call to/api/internal/users— carrying the caller's bearer token. That is the path traversal Cimpress reported (COR2-475, under the COR2-349 umbrella).fastmcp 4 percent-encodes path parameters, so the value stays inside a single URL segment and the traversal cannot be expressed at all. This fixes the cause rather than guarding the symptom, which is why it supersedes #15.
What changed
Import moves only — the OpenAPI types were relocated in 4.x, not redesigned:
MCPType,OpenAPITool,OpenAPIResource,OpenAPIResourceTemplate→fastmcp.server.providers.openapiHTTPRoute→fastmcp.utilities.openapi.modelsBoth callback signatures are unchanged (
RouteMapFn = Callable[[HTTPRoute, MCPType], MCPType | None]), socustom_route_mapperandcustomize_componentskeep their bodies verbatim.fastmcp 4 builds on
httpx2; the dependency is swapped accordingly. Applications callhttpx2.alias_httpx()once at startup so existingimport httpxcode shares the httpx2 classes — see cortexapps/cortex-remote-mcp#17.Testing
examplevalues from the spec). One semantic change worth a look: a singleoneOf+discriminatorbecameanyOf.tagOrId='../../internal/users'now resolves to/api/v1/catalog/%2E%2E%2F%2E%2E%2Finternal%2Fusers/openapiinstead of/api/internal/users.Merge order
This PR must merge before cortexapps/cortex-remote-mcp#17. That repo depends on
cortex-mcp @ master, and while this pinsfastmcp==2.12.3its install cannot resolve againstfastmcp>=4.0.5:Note
The removed pin comment claimed 2.12.3 was needed to fix a "PublicIdentifier schema bug." The tool-schema diff came back clean, but whoever hit that bug should confirm before merging.
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https://claude.ai/code/session_01LZtC15RMphgMhtsoDh4i4u