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fix: block redirect header leaks - #936
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…treamable HTTP client
The default reqwest client used `Policy::none()`, so any redirect from an
MCP server failed with `UnexpectedServerResponse("HTTP 307: ...")`.
It now follows 307 and 308 when the target has the same origin as the
original request, up to 10 hops. Those keep the method and body, so the
JSON-RPC message and the session, auth and custom headers arrive intact.
301, 302 and 303 are still returned to the caller, because following them
turns the POST into a bodyless GET. Cross-origin redirects are still
returned too, which keeps the header-leak guard.
Refs modelcontextprotocol#936
Reported-by: Mo (@trickyfalcon)
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…treamable HTTP client (#1367) * fix(transport): follow same-origin 307/308 redirects in the default Streamable HTTP client The default reqwest client used `Policy::none()`, so any redirect from an MCP server failed with `UnexpectedServerResponse("HTTP 307: ...")`. It now follows 307 and 308 when the target has the same origin as the original request, up to 10 hops. Those keep the method and body, so the JSON-RPC message and the session, auth and custom headers arrive intact. 301, 302 and 303 are still returned to the caller, because following them turns the POST into a bodyless GET. Cross-origin redirects are still returned too, which keeps the header-leak guard. Refs #936 Reported-by: Mo (@trickyfalcon) * docs(transport): describe redirect handling in default_http_client Document on `from_uri` and `from_config` which redirects the default client follows, that a 308 does not change the stored URI, and that a client passed to `with_client` keeps its own redirect policy. * docs(transport): move redirect rationale to same_origin_redirect_policy The rationale explains the policy, so it now sits on `same_origin_redirect_policy`, and the `default_http_client` doc points there instead of repeating the `from_uri` section. * test(transport): drop unused Default derive on CapturedRequest
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Motivation and Context
This fixes a security issue where the default reqwest-backed streamable HTTP transport could follow redirects while preserving caller-provided custom headers. Disabling automatic redirects keeps secrets such as custom API key headers scoped to the intended MCP server instead of replaying them to an attacker-controlled redirect target.
How Has This Been Tested?
Added a regression test
Breaking Changes
No
Types of changes
Checklist