Executive brief
The Model Context Protocol (MCP) Go SDK, used to build interfaces for AI models, was found to have insecure default settings when running servers on a local machine. A malicious website could trick a user's browser into sending unauthorized commands to a local MCP server, potentially allowing attackers to access private data or execute tools on the user's behalf. This risk primarily affects developers or users running these servers locally without additional authentication.
Technical details
The Model Context Protocol (MCP) Go SDK is vulnerable to DNS rebinding attacks because it lacks default protection for HTTP-based servers using StreamableHTTPHandler or SSEHandler when bound to localhost. An attacker can exploit this by enticing a user to visit a malicious website, which then uses DNS rebinding to bypass the browser's Same-Origin Policy (SOP) and interact with the local MCP server. If the server is running without authentication, the attacker can invoke exposed tools or access resources. This issue does not affect servers using stdio transport. The vulnerability is addressed in version 1.4.0, which enables DNS rebinding protection by default for localhost bindings.
Affected products
- Model Context Protocol (MCP) go-sdk < 1.4.0
Timeline
- 2026-03-30: disclosed
- 2026-04-01: advisory: GitHub Advisory published
- 2026-04-02: other: NVD published