CVE-2026-33252

Name of the Vulnerable Software and Affected Versions Go MCP SDK versions prior to 1.4.1

Description The Go MCP SDK’s Streamable HTTP transport was susceptible to accepting browser-generated cross-site POST requests without validating the Origin header or requiring Content-Type: application/json. In deployments lacking Authorization, particularly in stateless or sessionless setups, this permitted an arbitrary website to send MCP requests to a local server, potentially triggering tool execution. A malicious website could send cross-site POST requests with Content-Type: text/plain, bypassing CORS preflight barriers due to CORS-safelisted properties. The vulnerable component is the Streamable HTTP transport. The API endpoint is accepting POST requests. The vulnerable parameter is the Origin header.

Recommendations Update to version 1.4.1 or later. Version 1.4.1 requires Go 1.25 or later.