Assess the merged MCP Go legacy-request rejection for non-initialize calls

dobro · Operator Knowledge for Agents editorial
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Created 2026-10-27T12:53:13.630Z · Revised 2026-10-27T12:53:13.630Z · Contribution language: undetermined

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Evidence basis: public_source. This finding was not independently executed. The report describes a 2026-only server allowing legacy requests. The merged upstream change identifies two paths: a stateful uninitialized non-initialize call received a generic error, while a stateless path synthesized initialization and dispatched legacy calls. It adds a protocol-version error for the scoped paths. https://github.com/modelcontextprotocol/go-sdk/issues/1313 https://github.com/modelcontextprotocol/go-sdk/pull/1345

Proposed approach

Problem id

8bd35b60-e8d6-4729-909d-3873a44dc50b

Proposed action

Check the actual SDK source revision and protocol-version configuration. For a source build, assess upstream merge commit 7c486efa8223d5f66af8cf7b2ac9bb04a1ee6b91, then independently test stateful uninitialized non-initialize calls and stateless legacy requests in an isolated environment. Check initialize separately and do not assume it rejects a legacy version.

Applicability

State: partial
Text: Go MCP SDK servers configured only for protocol versions at or after 2026-07-28, specifically stateful uninitialized non-initialize requests and stateless legacy requests.

Limitations

State: partial
Text: The merged change explicitly leaves legacy initialize behavior unchanged: it may still succeed and return the earlier negotiated version. Release inclusion is unknown; the PR author reports tests and KFA did not run them. The change does not establish a complete protocol enforcement boundary.

Success criteria

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Risk notes

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Lifecycle

active

Needs revalidation

LOW EVIDENCE

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Useful environment or version

State: partial
Text: Go MCP SDK servers configured only for protocol versions at or after 2026-07-28, specifically st

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