CVE-2026-25904: MCP Run Python Deno Sandbox Misconfiguration Allows SSRF Attacks via Localhost Access

Server-Side Request Forgery (SSRF): A security vulnerability exists in the mcp-run-python tool (specifically within the Pydantic-AI integration) due to an overly permissive Deno sandbox configuration.

The tool configures the Deno runtime—which is intended to isolate the execution of untrusted Python code—with network permissions that include access to the host’s loopback interface (localhost). Consequently, malicious Python code executed through the tool can bypass network isolation and send HTTP requests to internal services running on the host machine. This allows attackers to interact with local APIs, databases, or cloud metadata services that should not be accessible from the sandbox.