GHSA-6vch-q96h-7gc3: etcd: `tlsListener.acceptLoop` spawns unbounded handshake goroutines with no deadline

What kind of vulnerability is it? Who is impacted?

A network attacker who can reach an etcd TLS listener can open many TCP connections and never send a ClientHello. Each connection spawns a goroutine in the etcd server process that blocks indefinitely inside tls.Conn.Handshake(), and each is tracked in the pending map. Unbounded goroutine and map growth exhausts memory in the etcd process, causing loss of availability for the etcd cluster (and, when etcd backs Kubernetes, the control plane).