Description
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.
Details
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:L
Affected Packages
| Software | From version | Fixed in |
|---|---|---|
| github.com/modelcontextprotocol/go-sdk | โ | โ |
| mcp-go-sdk | โ | 1.4.1 |
References
Similar Threats
- High CVE-2026-34742
- Unknown GO-2026-4770
- High GHSA-q382-vc8q-7jhj
- High CVE-2026-27896
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