Fleet: Observer-level enrollment secret extraction via ORDER BY oracle on Apple MDM commands endpoint

Fleet is an open-source device management platform built on osquery. In versions up to and including 4.84.1, the Apple MDM commands listing endpoint (GET /api/v1/fleet/mdm/apple/commands) allowed an authenticated user with the lowest-privilege Observer role to extract sensitive values from joined database tables, including host enrollment secrets and Apple Push Notification Service tokens, through a sort-order oracle. The endpoint accepted a user-supplied order_key parameter that was not validated against a column allowlist, and because the underlying query joins the hosts and nano_enrollments tables, an attacker could set the sort column to a sensitive field and combine it with the cursor-based after parameter to binary-search the value one character at a time, with the presence or absence of results revealing each character even though the value never appeared in the response. With extracted node_key or orbit_node_key values an attacker could impersonate enrolled hosts to Fleet's osquery and Orbit endpoints, submit fabricated host data, and retrieve pending scripts and commands. This issue is fixed in version 4.84.2.