From 784fa05025cb8cd0c770f99bc79d2794b9f85b6e Mon Sep 17 00:00:00 2001 From: Roman Arutyunyan Date: Thu, 29 Jan 2026 13:27:32 +0400 Subject: [PATCH] Upstream: detect premature plain text response from SSL backend. When connecting to a backend, the connection write event is triggered first in most cases. However if a response arrives quickly enough, both read and write events can be triggered together within the same event loop iteration. In this case the read event handler is called first and the write event handler is called after it. SSL initialization for backend connections happens only in the write event handler since SSL handshake starts with sending Client Hello. Previously, if a backend sent a quick plain text response, it could be parsed by the read event handler prior to starting SSL handshake on the connection. The change adds protection against parsing such responses on SSL-enabled connections. --- src/http/ngx_http_upstream.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/src/http/ngx_http_upstream.c b/src/http/ngx_http_upstream.c index df577ad67..cadc74479 100644 --- a/src/http/ngx_http_upstream.c +++ b/src/http/ngx_http_upstream.c @@ -2508,6 +2508,15 @@ ngx_http_upstream_process_header(ngx_http_request_t *r, ngx_http_upstream_t *u) return; } +#if (NGX_HTTP_SSL) + if (u->ssl && c->ssl == NULL) { + ngx_log_error(NGX_LOG_ERR, c->log, 0, + "upstream prematurely sent response"); + ngx_http_upstream_next(r, u, NGX_HTTP_UPSTREAM_FT_ERROR); + return; + } +#endif + u->state->bytes_received += n; u->buffer.last += n;