nginx: fix CVE-2026-28753

As per the advisory[1] mentioned in NVD[2], version 1.28.3 contains the fix.
Backport the commit[3] from 1.28.3 changelog matching the description.

[1] https://my.f5.com/manage/s/article/K000160367
[2] https://nvd.nist.gov/vuln/detail/CVE-2026-28753
[3] https://github.com/nginx/nginx/commit/6a8513761fb327f67fcc6cfcf1ad216887e2589f

Signed-off-by: Ankur Tyagi <ankur.tyagi85@gmail.com>
Signed-off-by: Anuj Mittal <anuj.mittal@oss.qualcomm.com>
This commit is contained in:
Ankur Tyagi
2026-04-09 23:22:07 +12:00
committed by Anuj Mittal
parent 24459e3f5c
commit 5124ac4a65
2 changed files with 94 additions and 0 deletions
@@ -0,0 +1,93 @@
From 7e705808a8568a091a8ecf418ed9f77914304fcc Mon Sep 17 00:00:00 2001
From: Roman Arutyunyan <arut@nginx.com>
Date: Thu, 26 Feb 2026 11:52:53 +0400
Subject: [PATCH] Mail: host validation.
Now host name resolved from client address is validated to only contain
the characters specified in RFC 1034, Section 3.5. The validation allows
to avoid injections when using the resolved host name in auth_http and
smtp proxy.
Reported by Asim Viladi Oglu Manizada, Colin Warren,
Xiao Liu (Yunnan University), Yuan Tan (UC Riverside), and
Bird Liu (Lanzhou University).
(cherry picked from commit 6a8513761fb327f67fcc6cfcf1ad216887e2589f)
CVE: CVE-2026-28753
Upstream-Status: Backport [https://github.com/nginx/nginx/commit/6a8513761fb327f67fcc6cfcf1ad216887e2589f]
Signed-off-by: Ankur Tyagi <ankur.tyagi85@gmail.com>
---
src/mail/ngx_mail_smtp_handler.c | 45 ++++++++++++++++++++++++++++++++
1 file changed, 45 insertions(+)
diff --git a/src/mail/ngx_mail_smtp_handler.c b/src/mail/ngx_mail_smtp_handler.c
index e68ceedfd..e477741c8 100644
--- a/src/mail/ngx_mail_smtp_handler.c
+++ b/src/mail/ngx_mail_smtp_handler.c
@@ -13,6 +13,7 @@
static void ngx_mail_smtp_resolve_addr_handler(ngx_resolver_ctx_t *ctx);
+static ngx_int_t ngx_mail_smtp_validate_host(ngx_str_t *name);
static void ngx_mail_smtp_resolve_name(ngx_event_t *rev);
static void ngx_mail_smtp_resolve_name_handler(ngx_resolver_ctx_t *ctx);
static void ngx_mail_smtp_block_reading(ngx_event_t *rev);
@@ -127,6 +128,20 @@ ngx_mail_smtp_resolve_addr_handler(ngx_resolver_ctx_t *ctx)
return;
}
+ if (ngx_mail_smtp_validate_host(&ctx->name) != NGX_OK) {
+ ngx_log_error(NGX_LOG_ERR, c->log, 0,
+ "%V resolved to invalid host name \"%V\"",
+ &c->addr_text, &ctx->name);
+
+ s->host = smtp_tempunavail;
+
+ ngx_resolve_addr_done(ctx);
+
+ ngx_mail_smtp_greeting(s, s->connection);
+
+ return;
+ }
+
c->log->action = "in resolving client hostname";
s->host.data = ngx_pstrdup(c->pool, &ctx->name);
@@ -149,6 +164,36 @@ ngx_mail_smtp_resolve_addr_handler(ngx_resolver_ctx_t *ctx)
}
+static ngx_int_t
+ngx_mail_smtp_validate_host(ngx_str_t *name)
+{
+ u_char ch;
+ ngx_uint_t i;
+
+ if (name->len == 0) {
+ return NGX_DECLINED;
+ }
+
+ for (i = 0; i < name->len; i++) {
+ ch = name->data[i];
+
+ /* allow only characters from RFC 1034, Section 3.5 */
+
+ if ((ch >= 'a' && ch <= 'z')
+ || (ch >= 'A' && ch <= 'Z')
+ || (ch >= '0' && ch <= '9')
+ || ch == '-' || ch == '.')
+ {
+ continue;
+ }
+
+ return NGX_DECLINED;
+ }
+
+ return NGX_OK;
+}
+
+
static void
ngx_mail_smtp_resolve_name(ngx_event_t *rev)
{
@@ -7,6 +7,7 @@ SRC_URI:append = " \
file://CVE-2026-28755.patch \
file://CVE-2026-27651.patch \
file://CVE-2026-27654.patch \
file://CVE-2026-28753.patch \
"
SRC_URI[sha256sum] = "77a2541637b92a621e3ee76776c8b7b40cf6d707e69ba53a940283e30ff2f55d"