CVE-2026-52870 is a missing authorization vulnerability (CWE-862) in Anthropic's official Model Context Protocol Python SDK that allows any client on a shared server to enumerate, read, and cancel tasks belonging to other clients.

The default request handlers registered by the experimental enabletasks() helper operate on task IDs alone without checking caller identity, storing active workflows in a single global server store.

The vulnerability was patched in mcp version 1.27.2, and operators of multi-client MCP gateways are advised to upgrade immediately.