GHSA-C9XM-49CP-XCR9 rmcp OAuth client fetches server-controlled resource_metadata URLs

Summary The rmcp OAuth client accepts a server-controlled resourcemetadata= URL from the WWW-Authenticate header and fetches it without same-origin or private-network validation. An attacker-controlled MCP server can return a 401 WWW-Authenticate: Bearer resourcemetadata="..." header pointing at ...

CVE-2026-63127

creationtimestamp| type| source ---|---|--- 2026-09-17 00:35:09+00:00| published-proof-of-concept| https://github.com/modelcontextprotocol/rust-sdk/security/advisories/GHSA-33f5-2c5q-wgwj 2026-09-17 03:31:23+00:00| seen| https://gist.github.com/alon710/16597bd55d59e6c89394c487c227381c...