diff --git a/usr.sbin/httpd/httpd.conf.5 b/usr.sbin/httpd/httpd.conf.5
index be31341b5fa..1d6f72a8d9a 100644
--- a/usr.sbin/httpd/httpd.conf.5
+++ b/usr.sbin/httpd/httpd.conf.5
@@ -1,4 +1,4 @@
-.\"	$OpenBSD: httpd.conf.5,v 1.130 2026/05/17 10:56:41 kirill Exp $
+.\"	$OpenBSD: httpd.conf.5,v 1.131 2026/06/01 09:28:42 claudio Exp $
 .\"
 .\" Copyright (c) 2014, 2015 Reyk Floeter <reyk@openbsd.org>
 .\"
@@ -14,7 +14,7 @@
 .\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 .\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 .\"
-.Dd $Mdocdate: May 17 2026 $
+.Dd $Mdocdate: June 1 2026 $
 .Dt HTTPD.CONF 5
 .Os
 .Sh NAME
@@ -404,6 +404,15 @@ This allows FastCGI server chroot to be a directory under httpd chroot.
 .It Ic param Ar variable value
 Sets a variable that will be sent to the FastCGI server.
 Each statement defines one variable.
+.It Ic pass Ic chunked
+Allow chunked uploads to be passed to the FastCGI server.
+By default data uploads with
+.Ar Transfer-Encoding: chunked
+are forbidden.
+By setting
+.Ic pass Ic chunked
+uploads with chunked encoding are accepted but because the CONTENT_LENGTH
+variable can not be set it violates the CGI speficfication.
 .El
 .Pp
 The FastCGI handler will be given the following variables by default:
diff --git a/usr.sbin/httpd/httpd.h b/usr.sbin/httpd/httpd.h
index 2f4952c4870..af36aec7d59 100644
--- a/usr.sbin/httpd/httpd.h
+++ b/usr.sbin/httpd/httpd.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: httpd.h,v 1.172 2026/05/17 10:56:41 kirill Exp $	*/
+/*	$OpenBSD: httpd.h,v 1.173 2026/06/01 09:28:42 claudio Exp $	*/
 
 /*
  * Copyright (c) 2006 - 2015 Reyk Floeter <reyk@openbsd.org>
@@ -108,7 +108,8 @@ enum httpchunk {
 	TOREAD_HTTP_CHUNK_LENGTH	= -3,
 	TOREAD_HTTP_CHUNK_TRAILER	= -4,
 	TOREAD_HTTP_NONE		= -5,
-	TOREAD_HTTP_RANGE		= TOREAD_HTTP_CHUNK_LENGTH
+	TOREAD_HTTP_RANGE		= TOREAD_HTTP_CHUNK_LENGTH,
+	TOREAD_HTTP_FINAL_CHUNK_TRAILER	= -6,
 };
 
 #if DEBUG
@@ -544,6 +545,7 @@ struct server_config {
 
 	struct server_fcgiparams fcgiparams;
 	int			 fcgistrip;
+	int			 fcgiallowchunked;
 	char			 errdocroot[HTTPD_ERRDOCROOT_MAX];
 
 	TAILQ_ENTRY(server_config) entry;
@@ -711,7 +713,7 @@ void	 server_file_error(struct bufferevent *, short, void *);
 
 /* server_fcgi.c */
 int	 server_fcgi(struct httpd *, struct client *);
-int	 fcgi_add_stdin(struct client *, struct evbuffer *);
+int	 fcgi_add_stdin(struct client *, const char *, size_t);
 
 /* httpd.c */
 void		 event_again(struct event *, int, short,
diff --git a/usr.sbin/httpd/parse.y b/usr.sbin/httpd/parse.y
index 9233cc6b8ad..d6bc3354583 100644
--- a/usr.sbin/httpd/parse.y
+++ b/usr.sbin/httpd/parse.y
@@ -1,4 +1,4 @@
-/*	$OpenBSD: parse.y,v 1.134 2026/05/17 10:56:41 kirill Exp $	*/
+/*	$OpenBSD: parse.y,v 1.135 2026/06/01 09:28:42 claudio Exp $	*/
 
 /*
  * Copyright (c) 2020 Matthias Pressfreund <mpfr@fn.de>
@@ -833,6 +833,16 @@ fcgiflags	: SOCKET STRING {
 			}
 			srv_conf->fcgistrip = $2;
 		}
+		| PASS STRING {
+			if (strcmp($2, "chunked") != 0) {
+				yyerror("Invalid token '%s' expected 'chunked'",
+				    $2);
+				free($2);
+				YYERROR;
+			}
+			srv_conf->fcgiallowchunked = 1;
+			free($2);
+		}
 		;
 
 connection	: CONNECTION '{' optnl conflags_l '}'
diff --git a/usr.sbin/httpd/server_fcgi.c b/usr.sbin/httpd/server_fcgi.c
index 5c4a8d3434e..15e5ee8c5d8 100644
--- a/usr.sbin/httpd/server_fcgi.c
+++ b/usr.sbin/httpd/server_fcgi.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: server_fcgi.c,v 1.100 2026/03/02 19:24:58 rsadowski Exp $	*/
+/*	$OpenBSD: server_fcgi.c,v 1.101 2026/06/01 09:28:42 claudio Exp $	*/
 
 /*
  * Copyright (c) 2014 Florian Obser <florian@openbsd.org>
@@ -388,7 +388,7 @@ server_fcgi(struct httpd *env, struct client *clt)
 		bufferevent_enable(clt->clt_bev, EV_READ);
 	} else {
 		bufferevent_disable(clt->clt_bev, EV_READ);
-		fcgi_add_stdin(clt, NULL);
+		fcgi_add_stdin(clt, NULL, 0);
 	}
 
 	if (strcmp(desc->http_version, "HTTP/1.1") == 0) {
@@ -414,7 +414,7 @@ server_fcgi(struct httpd *env, struct client *clt)
 }
 
 int
-fcgi_add_stdin(struct client *clt, struct evbuffer *evbuf)
+fcgi_add_stdin(struct client *clt, const char *buf, size_t len)
 {
 	struct fcgi_record_header	h;
 
@@ -424,16 +424,16 @@ fcgi_add_stdin(struct client *clt, struct evbuffer *evbuf)
 	h.id = htons(1);
 	h.padding_len = 0;
 
-	if (evbuf == NULL) {
+	if (len == 0) {
 		h.content_len = 0;
 		return bufferevent_write(clt->clt_srvbev, &h,
 		    sizeof(struct fcgi_record_header));
 	} else {
-		h.content_len = htons(EVBUFFER_LENGTH(evbuf));
+		h.content_len = htons(len);
 		if (bufferevent_write(clt->clt_srvbev, &h,
 		    sizeof(struct fcgi_record_header)) == -1)
 			return -1;
-		return bufferevent_write_buffer(clt->clt_srvbev, evbuf);
+		return bufferevent_write(clt->clt_srvbev, buf, len);
 	}
 	return (0);
 }
diff --git a/usr.sbin/httpd/server_http.c b/usr.sbin/httpd/server_http.c
index fb3ec67ae0e..dd7bac10561 100644
--- a/usr.sbin/httpd/server_http.c
+++ b/usr.sbin/httpd/server_http.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: server_http.c,v 1.162 2026/05/17 10:56:41 kirill Exp $	*/
+/*	$OpenBSD: server_http.c,v 1.163 2026/06/01 09:28:42 claudio Exp $	*/
 
 /*
  * Copyright (c) 2020 Matthias Pressfreund <mpfr@fn.de>
@@ -512,11 +512,11 @@ server_read_httpcontent(struct bufferevent *bev, void *arg)
 {
 	struct client		*clt = arg;
 	struct evbuffer		*src = EVBUFFER_INPUT(bev);
-	size_t			 size;
+	const char		*buf = EVBUFFER_DATA(src);
+	size_t			 size = EVBUFFER_LENGTH(src);
 
 	getmonotime(&clt->clt_tv_last);
 
-	size = EVBUFFER_LENGTH(src);
 	DPRINTF("%s: session %d: size %lu, to read %lld", __func__,
 	    clt->clt_id, size, clt->clt_toread);
 	if (!size)
@@ -524,21 +524,18 @@ server_read_httpcontent(struct bufferevent *bev, void *arg)
 
 	if (clt->clt_toread > 0) {
 		/* Read content data */
-		if ((off_t)size > clt->clt_toread) {
+		if ((off_t)size > clt->clt_toread)
 			size = clt->clt_toread;
-			if (fcgi_add_stdin(clt, src) == -1)
-				goto fail;
-			clt->clt_toread = 0;
-		} else {
-			if (fcgi_add_stdin(clt, src) == -1)
-				goto fail;
-			clt->clt_toread -= size;
-		}
+
+		if (fcgi_add_stdin(clt, buf, size) == -1)
+			goto fail;
+		evbuffer_drain(src, size);
+		clt->clt_toread -= size;
 		DPRINTF("%s: done, size %lu, to read %lld", __func__,
 		    size, clt->clt_toread);
 	}
 	if (clt->clt_toread == 0) {
-		fcgi_add_stdin(clt, NULL);
+		fcgi_add_stdin(clt, NULL, 0);
 		clt->clt_toread = TOREAD_HTTP_HEADER;
 		bufferevent_disable(bev, EV_READ);
 		bev->readcb = server_read_http;
@@ -561,13 +558,13 @@ server_read_httpchunks(struct bufferevent *bev, void *arg)
 {
 	struct client		*clt = arg;
 	struct evbuffer		*src = EVBUFFER_INPUT(bev);
+	const char		*buf = EVBUFFER_DATA(src);
+	size_t			 size = EVBUFFER_LENGTH(src);
 	char			*line;
 	long long		 llval;
-	size_t			 size;
 
 	getmonotime(&clt->clt_tv_last);
 
-	size = EVBUFFER_LENGTH(src);
 	DPRINTF("%s: session %d: size %lu, to read %lld", __func__,
 	    clt->clt_id, size, clt->clt_toread);
 	if (!size)
@@ -575,17 +572,15 @@ server_read_httpchunks(struct bufferevent *bev, void *arg)
 
 	if (clt->clt_toread > 0) {
 		/* Read chunk data */
-		if ((off_t)size > clt->clt_toread) {
+		if ((off_t)size > clt->clt_toread)
 			size = clt->clt_toread;
-			if (server_bufferevent_write_chunk(clt, src, size)
-			    == -1)
-				goto fail;
-			clt->clt_toread = 0;
-		} else {
-			if (server_bufferevent_write_buffer(clt, src) == -1)
-				goto fail;
-			clt->clt_toread -= size;
-		}
+		if (fcgi_add_stdin(clt, buf, size) == -1)
+			goto fail;
+		clt->clt_toread -= size;
+		evbuffer_drain(src, size);
+
+		if (clt->clt_toread == 0)
+			clt->clt_toread = TOREAD_HTTP_CHUNK_TRAILER;
 		DPRINTF("%s: done, size %lu, to read %lld", __func__,
 		    size, clt->clt_toread);
 	}
@@ -612,18 +607,15 @@ server_read_httpchunks(struct bufferevent *bev, void *arg)
 			return;
 		}
 
-		if (server_bufferevent_print(clt, line) == -1 ||
-		    server_bufferevent_print(clt, "\r\n") == -1) {
-			free(line);
-			goto fail;
-		}
 		free(line);
 
 		if ((clt->clt_toread = llval) == 0) {
 			DPRINTF("%s: last chunk", __func__);
-			clt->clt_toread = TOREAD_HTTP_CHUNK_TRAILER;
+			fcgi_add_stdin(clt, NULL, 0);
+			clt->clt_toread = TOREAD_HTTP_FINAL_CHUNK_TRAILER;
 		}
 		break;
+	case TOREAD_HTTP_FINAL_CHUNK_TRAILER:
 	case TOREAD_HTTP_CHUNK_TRAILER:
 		/* Last chunk is 0 bytes followed by trailer and empty line */
 		line = evbuffer_readln(src, NULL, EVBUFFER_EOL_CRLF_STRICT);
@@ -632,15 +624,15 @@ server_read_httpchunks(struct bufferevent *bev, void *arg)
 			bufferevent_enable(bev, EV_READ);
 			return;
 		}
-		if (server_bufferevent_print(clt, line) == -1 ||
-		    server_bufferevent_print(clt, "\r\n") == -1) {
-			free(line);
-			goto fail;
-		}
 		if (strlen(line) == 0) {
 			/* Switch to HTTP header mode */
-			clt->clt_toread = TOREAD_HTTP_HEADER;
-			bev->readcb = server_read_http;
+			if (clt->clt_toread == TOREAD_HTTP_CHUNK_TRAILER) {
+				clt->clt_toread = TOREAD_HTTP_CHUNK_LENGTH;
+			} else {
+				clt->clt_toread = TOREAD_HTTP_HEADER;
+				bufferevent_disable(bev, EV_READ);
+				bev->readcb = server_read_http;
+			}
 		}
 		free(line);
 		break;
@@ -648,8 +640,6 @@ server_read_httpchunks(struct bufferevent *bev, void *arg)
 		/* Chunk is terminated by an empty newline */
 		line = evbuffer_readln(src, NULL, EVBUFFER_EOL_CRLF_STRICT);
 		free(line);
-		if (server_bufferevent_print(clt, "\r\n") == -1)
-			goto fail;
 		clt->clt_toread = TOREAD_HTTP_CHUNK_LENGTH;
 		break;
 	}
@@ -1465,6 +1455,11 @@ server_response(struct httpd *httpd, struct client *clt)
 		server_abort_http(clt, 413, "request body too large");
 		return (-1);
 	}
+	if (desc->http_chunked && !srv_conf->fcgiallowchunked) {
+		server_abort_http(clt, 400,
+		    "Transfer-Encoding: chunked not allowed");
+		return (-1);
+	}
 
 	if (srv_conf->flags & SRVFLAG_BLOCK) {
 		server_abort_http(clt, srv_conf->return_code,