CVE-2026-33252 Details

A vulnerability in the Go Model Context Protocol (MCP) SDK's Streamable HTTP transport allowed cross-site `POST` requests to be accepted without proper validation of the `Origin` header or enforcement of the `Content-Type: application/json` requirement. This issue was present in versions through 1.4.0. In environments lacking authorization, particularly those that are stateless or sessionless, it enabled arbitrary websites to send MCP requests to a local server, potentially triggering the execution of tools. The vulnerability arose because the HTTP transport did not verify the origin of requests, leaving a gap that could be exploited by malicious sites.

Users are advised to update the Go MCP SDK to version 1.4.1 or later, which includes the necessary validation of the `Content-Type` header and origin verification for `POST` requests. Version 1.4.1 requires Go 1.25 or later.