GHSA-xw59-hvm2-8pj6: DNS Rebinding Protection Disabled by Default in Model Context Protocol Go SDK for Servers Running on Localhost

Summary

The Model Context Protocol (MCP) Go SDK does not enable DNS rebinding protection by default for HTTP-based servers. A malicious website could use DNS rebinding to bypass same-origin restrictions and send requests to an HTTP-based MCP server running on localhost without authentication, using `StreamableHTTPHandler` or `SSEHandler`. This could let an attacker invoke tools or access resources on the user's behalf, and servers using stdio transport are not affected.

Mitigation

Fixed in 1.4.0: servers created via `StreamableHTTPHandler` or `SSEHandler` now have DNS rebinding protection enabled by default when binding to `localhost`. Users are advised to update to version 1.4.0.

Topics

• Model Context Protocol

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