Security fixes target the current stable SDK and CLI release lines:

Older lines receive best-effort fixes only. A vulnerability may require upgrading to the latest stable line when a safe backport would break protocol correctness or public API compatibility.

Do not open a public issue for a suspected vulnerability. Use GitHub private vulnerability reporting and include:

• affected versions and platforms;
• transport and negotiated MCP version;
• reproduction steps or a proof of concept;
• expected impact and any known mitigation.

Maintainers commit to acknowledging a complete report within two business days. Please allow time to coordinate a fix and disclosure before publishing details.

A vulnerability with CVSS 7.0 or higher is P0 under the MCP SDK tiering policy. Maintainers commit to resolving it within seven calendar days after validation. Resolution means a released fix or a documented safe mitigation that removes user exposure. If a final upstream fix remains outstanding, the advisory will track that follow-up separately.

Security fixes receive focused regression tests and the affected analyzer, unit, transport, conformance, interoperability, and release checks. Public advisories credit reporters who want attribution and are published after a fixed version or mitigation is available.

Reports are especially useful for:

• JSON-RPC or MCP message validation bypasses;
• authentication, OAuth, redirect, issuer, token, Origin, or Host validation;
• cross-request data leakage or request-ID confusion;
• unsafe URI, header, schema-reference, file, or process handling;
• dependency vulnerabilities reachable through supported SDK behavior.

Application-specific authorization policy, insecure deployment configuration, and plaintext storage copied from explicitly local learning examples are outside the SDK vulnerability boundary unless the SDK makes the safe behavior impossible.