CVE-2026-33252: Cross-Site Tool Execution for HTTP Servers without Authorizatrion in github.com/modelcontextprotocol/go-sdk

March 19, 2026

The Go SDK’s Streamable HTTP transport accepted browser-generated cross-site POST requests without validating the Origin header and without requiring Content-Type: application/json. In deployments without Authorization, especially stateless or sessionless configurations, this allows an arbitrary website to send MCP requests to a local server and potentially trigger tool execution.

References

github.com/advisories/GHSA-89xv-2j6f-qhc8
github.com/modelcontextprotocol/go-sdk
github.com/modelcontextprotocol/go-sdk/commit/a433a831d6e5d5ac3b9e625a8095aa8eaa040dfc
github.com/modelcontextprotocol/go-sdk/security/advisories/GHSA-89xv-2j6f-qhc8
nvd.nist.gov/vuln/detail/CVE-2026-33252

Code Behaviors & Features

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