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nginx: Mitigate HTTP/2 Stream Resets Flood impact

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Reduces the impact of HTTP/2 Stream Reset flooding in the nginx product
(CVE-2023-44487).

See: https://www.nginx.com/blog/http-2-rapid-reset-attack-impacting-f5-nginx-products/

This patch only reduces the impact and does not completely mitigate the CVE
in question, the latter being due to a design flaw in the HTTP/2 protocol
itself. For transparancy reasons I therefore opted to not mark the
CVE as resolved, so that integrators can decide for themselves, wheither to
enable HTTP/2 support or allow HTTP/1.1 connections only.

Signed-off-by: Jasper Orschulko <jasper@fancydomain.eu>
Signed-off-by: Armin Kuster <akuster808@gmail.com>
This commit is contained in:
Jasper Orschulko 2023-11-27 01:04:17 +01:00 committed by Armin Kuster
parent a005377cdf
commit a1c4d361ed
3 changed files with 95 additions and 0 deletions
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92
meta-webserver/recipes-httpd/nginx/files/0001-HTTP-2-per-iteration-stream-handling-limit.patch Normal file
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@ -0,0 +1,92 @@
From 2b9667f36551406169e3e2a6a774466ac70a83c0 Mon Sep 17 00:00:00 2001
From: Maxim Dounin <mdounin@mdounin.ru>
Date: Tue, 10 Oct 2023 15:13:39 +0300
Subject: [PATCH] HTTP/2: per-iteration stream handling limit.
To ensure that attempts to flood servers with many streams are detected
early, a limit of no more than 2 * max_concurrent_streams new streams per one
event loop iteration was introduced. This limit is applied even if
max_concurrent_streams is not yet reached - for example, if corresponding
streams are handled synchronously or reset.
Further, refused streams are now limited to maximum of max_concurrent_streams
and 100, similarly to priority_limit initial value, providing some tolerance
to clients trying to open several streams at the connection start, yet
low tolerance to flooding attempts.
Upstream-Status: Backport
[https://github.com/nginx/nginx/commit/6ceef192e7af1c507826ac38a2d43f08bf265fb9]
Reduces the impact of HTTP/2 Stream Reset flooding in the nginx product
(CVE-2023-44487).
See: https://www.nginx.com/blog/http-2-rapid-reset-attack-impacting-f5-nginx-products/
This patch only reduces the impact and does not completely mitigate the CVE
in question, the latter being due to a design flaw in the HTTP/2 protocol
itself. For transparancy reasons I therefore opted to not mark the
CVE as resolved, so that integrators can decide for themselves, wheither to
enable HTTP/2 support or allow HTTP/1.1 connections only.
Signed-off-by: Jasper Orschulko <jasper@fancydomain.eu>
---
src/http/v2/ngx_http_v2.c | 15 +++++++++++++++
src/http/v2/ngx_http_v2.h | 2 ++
2 files changed, 17 insertions(+)
diff --git a/src/http/v2/ngx_http_v2.c b/src/http/v2/ngx_http_v2.c
index 3611a2e50..291677aca 100644
--- a/src/http/v2/ngx_http_v2.c
+++ b/src/http/v2/ngx_http_v2.c
@@ -361,6 +361,7 @@ ngx_http_v2_read_handler(ngx_event_t *rev)
ngx_log_debug0(NGX_LOG_DEBUG_HTTP, c->log, 0, "http2 read handler");
h2c->blocked = 1;
+ h2c->new_streams = 0;
if (c->close) {
c->close = 0;
@@ -1320,6 +1321,14 @@ ngx_http_v2_state_headers(ngx_http_v2_connection_t *h2c, u_char *pos,
goto rst_stream;
}
+ if (h2c->new_streams++ >= 2 * h2scf->concurrent_streams) {
+ ngx_log_error(NGX_LOG_INFO, h2c->connection->log, 0,
+ "client sent too many streams at once");
+
+ status = NGX_HTTP_V2_REFUSED_STREAM;
+ goto rst_stream;
+ }
+
if (!h2c->settings_ack
&& !(h2c->state.flags & NGX_HTTP_V2_END_STREAM_FLAG)
&& h2scf->preread_size < NGX_HTTP_V2_DEFAULT_WINDOW)
@@ -1385,6 +1394,12 @@ ngx_http_v2_state_headers(ngx_http_v2_connection_t *h2c, u_char *pos,
rst_stream:
+ if (h2c->refused_streams++ > ngx_max(h2scf->concurrent_streams, 100)) {
+ ngx_log_error(NGX_LOG_INFO, h2c->connection->log, 0,
+ "client sent too many refused streams");
+ return ngx_http_v2_connection_error(h2c, NGX_HTTP_V2_NO_ERROR);
+ }
+
if (ngx_http_v2_send_rst_stream(h2c, h2c->state.sid, status) != NGX_OK) {
return ngx_http_v2_connection_error(h2c, NGX_HTTP_V2_INTERNAL_ERROR);
}
diff --git a/src/http/v2/ngx_http_v2.h b/src/http/v2/ngx_http_v2.h
index 349229711..6a7aaa62c 100644
--- a/src/http/v2/ngx_http_v2.h
+++ b/src/http/v2/ngx_http_v2.h
@@ -125,6 +125,8 @@ struct ngx_http_v2_connection_s {
ngx_uint_t processing;
ngx_uint_t frames;
ngx_uint_t idle;
+ ngx_uint_t new_streams;
+ ngx_uint_t refused_streams;
ngx_uint_t priority_limit;
ngx_uint_t pushing;
--
2.42.1

1
meta-webserver/recipes-httpd/nginx/nginx_1.16.1.bb
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@ -7,4 +7,5 @@ SRC_URI[sha256sum] = "f11c2a6dd1d3515736f0324857957db2de98be862461b5a542a3ac6188
SRC_URI += "file://CVE-2019-20372.patch \
file://CVE-2022-41741-CVE-2022-41742.patch \
file://0001-HTTP-2-per-iteration-stream-handling-limit.patch \
"

2
meta-webserver/recipes-httpd/nginx/nginx_1.17.8.bb
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@ -8,3 +8,5 @@ LIC_FILES_CHKSUM = "file://LICENSE;md5=52e384aaac868b755b93ad5535e2d075"
SRC_URI[md5sum] = "29cd861a13aae69a058cbabaae86177b"
SRC_URI[sha256sum] = "97d23ecf6d5150b30e284b40e8a6f7e3bb5be6b601e373a4d013768d5a25965b"
SRC_URI += "file://0001-HTTP-2-per-iteration-stream-handling-limit.patch"