Vulnerability Details CVE-2026-33252
The Go MCP SDK used Go's standard encoding/json. Prior to version 1.4.1, 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. Version 1.4.1 contains a patch for the issue.
Exploit prediction scoring system (EPSS) score
EPSS Score 0.0
EPSS Ranking 0.5%
CVSS Severity
CVSS v3 Score 7.1
References
Products affected by CVE-2026-33252
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cpe:2.3:a:lfprojects:mcp_go_sdk:*