CVE-2026-61546

AnkiMCP is an Anki addon that implements an MCP server, enabling AI assistants to interact with the Anki flashcard application. Prior to version 0.21.0, anki mcp server/mcp server.py globally disables FastMCP DNS-rebinding protection through TransportSecuritySettings with enable dns rebinding protection=False, including for the default local Streamable HTTP listener. The defaults in anki mcp server/config.py enable http enabled on 127.0.0.1:3141, with an empty http path selecting the root endpoint. No bearer token, API key, session secret, strict Host allowlist or strict Origin allowlist is enforced before initialize, tools/list and tools/call reach MCP dispatch. A victim who visits a malicious web page while Anki and the listener are running can have browser requests rebound to loopback, allowing the attacker to initialize MCP, enumerate tools, read the local collection, and perform enabled non-destructive note/deck creation or updates. The attacker needs neither LAN position nor a local process. Available operations depend on enabled tool filters; destructive tools are hidden unless enabled destructive tools is opted into, limiting deletion-level impact but not the exposed read/write operations. The reported harness confirms real MCP tool dispatch with substituted Anki bridge responses rather than demonstrating destructive changes to a real collection. Disabling protection for tunnels/proxies also disables it for the normal loopback configuration. This issue is fixed in version 0.21.0.