Next.js router-server WebSocket upgrade SSRF (CVE-2026-44578)

Exploits CVE-2026-44578: WebSocket upgrade handler proxies absolute http:// request-line URIs GET, port 80 without honouring finished/308 from normalizeRepeatedSlashes. Actions: test confirm, aws / azure IMDS harvest, custom ssrfurl. Self-hosted only; Vercel/nginx often block. Fixed in 15.5.16 /...