@fastify/reply-from v12.6.1 and earlier and @fastify/http-proxy v11.4.3 and earlier process the client's Connection header after the proxy has added its own headers via rewriteRequestHeaders.
CVSS 4.0CRITICAL 9.0·Network·No auth·No interaction·EPSS 0.00441·Published 2026-04-15·Fixed in 12.6.2, 11.4.4CWE-644
Impact: @fastify/http-proxy versions from 9.4.0 up to and including 11.5.0 fail to validate the resolved WebSocket destination path against the configured rewrite prefix.
CVSS 3.1CRITICAL 10.0·Network·No auth·No interaction·EPSS 0.00501·Published 2026-07-18·Fixed in 11.6.0CWE-22
@fastify/http-proxy versions before 11.6.2 do not validate proxied HTTP request paths for backslash based dot-segments before forwarding them to the configured upstream.