CVE-2026-53520: Nezha Monitoring: Authenticated users can claim the dashboard Host through NAT and preempt all dashboard routing

An authenticated non-admin user who owns any server can create or update a NAT profile whose domain is equal to the dashboard’s own HTTP Host (for example, dashboard.example:8008). The dashboard’s top-level HTTP/gRPC multiplexer checks NATShared.GetNATConfigByDomain(r.Host) before dispatching requests to the dashboard API, frontend, or gRPC handler, so a member-controlled NAT profile for the dashboard Host takes precedence over the real dashboard.

A disabled claimed NAT profile blocks matching dashboard requests before they reach the dashboard handler. An enabled claimed NAT profile routes matching requests into ServeNAT, which sends a NAT task to the member’s selected agent and wraps the original HTTP request into the NAT IO stream. This allows a low-privileged dashboard user to take over routing for a global host name that should be reserved for the dashboard operator.

Tested locally against commit 8b5e382fe217107c7b777ea9c6b4bc3d2e156202 of github.com/nezhahq/nezha.