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archivevulnerability · 16 Sep 2026 · 22:13 UTC

GHSA-33f5-2c5q-wgwj: RMCP: Missing Resource Field Validation in OAuth Protected Resource Metadata Discovery

VULNCVE-2026-63127source · GTH
HIGHHigh-risk vulnerability — CVSS 8.2

last 60 dispatches · spectrum

### Summary The `rmcp` library does not validate the `resource` parameter in OAuth Protected Resource metadata (RFC 9728), allowing a malicious MCP server to redirect OAuth flows to a legitimate authorization server and steal the resulting access tokens. ### Details RFC 9728 specifies two MUST requirements for resource parameter validation: - Section 7.3: the client MUST ensure that the resource identifier URL it is using as the prefix for the metadata request exactly matches the `resource` value in the returned metadata document. …

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