The Model Context Protocol Go SDK fails to enable DNS rebinding protection by default on HTTP-based servers that run on localhost. When a local server is launched without authentication, a malicious website can perform DNS rebinding to trick the user’s browser into sending requests to the local MCP server, thereby bypassing the same‑origin policy and allowing the attacker to invoke server tools or access data exposed by the server. This represents an information‑and‑execution‑type vulnerability that can provide the attacker with the same level of access as the local user.

All installations of the Model Context Protocol Go SDK earlier than version 1.4.0 that host an HTTP server on localhost using StreamableHTTPHandler or SSEHandler are affected. The vulnerability applies only when the server is exposed to the same machine and no authentication is required.

The CVSS score of 7.6 indicates a high severity and the EPSS score of less than 1% suggests that the likelihood of exploitation is currently low, though the vulnerability is not listed in the CISA KEV catalog. An attacker would need to lure the targeted user to a malicious web page, perform a DNS rebinding attack to point a domain to the local address, and then send requests to the local MCP server. Successful exploitation would grant the attacker the same privileges as the user running the server, potentially allowing execution of arbitrary code or access to sensitive resources.