rmcp, the official Rust MCP SDK, took four advisories in one day, two of them high.

CVE-2026-63127 (8.2) covers crates/rmcp/src/transport/auth.rs omitting the RFC 9728 resource field and never confirming the returned resource identifier matches the configured MCP server, so a hostile server publishes metadata for a different legitimate resource and you finish the OAuth flow holding a token minted for someone else's server. GHSA-c9xm-49cp-xcr9 covers the same file fetching an attacker-supplied resource_metadata= URL from WWW-Authenticate with no same-origin or private-network check, an SSRF reaching localhost, RFC 1918 space and cloud metadata endpoints. CVE-2026-63128 (7.5) leaks a LocalSessionHandle per malformed JSON-RPC POST because handle_post allocates the session before validating the body; the reproduction sustains 2,000 leak requests per second, about 170 million entries and 75 GB resident per day. The fixes span 1.4.0, 2.0.0 and 2.1.0, so one upgrade doesn't clear all four. The last three days of MCP advisories hit individual servers. These hit the SDK every server is built on.