Model Context Protocol Python SDK: Client fetched server-chosen $ref URLs while validating tool results against output schemas

影響: pip:mcp >= 2.0.0, < 2.2.0 → 2.2.0, pip:mcp >= 1.10.0, < 1.30.0 → 1.30.0

In affected versions, when a connected MCP server declared an outputSchema for a tool, the SDK's client validated each call_tool result with jsonschema's default resolver, which fetches any $ref it cannot resolve locally by opening the URL. A server could therefore put an http://, https:// or file:// reference in a tool's output schema and make the client: - request that URL, or read that local file, from the client's own network position on every call of the tool (the content was used only as…

Read on GitHub Advisory Database

On 10/28/2026, 06:05 AM, GitHub Advisory Database published "Model Context Protocol Python SDK: Client fetched server-chosen $ref URLs while validating tool results against output schemas" (type: Advisory). Severity is "Medium" (medium). Related technologies: Python. CVE: CVE-2026-116686.