SECURITY UPDATE: plain text response injection via a premature
response from an SSL-proxied upstream
debian/patches/CVE-2026-1642.patch: reject a response received in
ngx_http_upstream_process_header before the upstream SSL handshake
has started (u->ssl set, c->ssl still NULL) and retry the next
upstream, so a man-in-the-middle on the proxy-to-upstream path can
no longer have plain text data parsed as the upstream response