From f20bc39fcb704b55457fcc69d30e8df2edbd3cdd Mon Sep 17 00:00:00 2001
From: Marten Seemann <martenseemann@gmail.com>
Date: Wed, 25 Oct 2023 11:04:24 +0700
Subject: [PATCH] crypto/tls: check client's supported versions when using QUIC

According to RFC 9001 Section 4.2, the client MUST NOT offer any TLS version
older than 1.3.

Fixes #63723.

Change-Id: Ia92f98274ca784e2bc151faf236380af51f699c1
Reviewed-on: https://go-review.googlesource.com/c/go/+/537576
Reviewed-by: Filippo Valsorda <filippo@golang.org>
Auto-Submit: Filippo Valsorda <filippo@golang.org>
Reviewed-by: Roland Shoemaker <roland@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Damien Neil <dneil@google.com>
---
 handshake_server_tls13.go | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/handshake_server_tls13.go b/handshake_server_tls13.go
index 07b1a38..21d798d 100644
--- a/handshake_server_tls13.go
+++ b/handshake_server_tls13.go
@@ -240,8 +240,15 @@ GroupSelection:
 	c.clientProtocol = selectedProto
 
 	if c.quic != nil {
+		// RFC 9001 Section 4.2: Clients MUST NOT offer TLS versions older than 1.3.
+		for _, v := range hs.clientHello.supportedVersions {
+			if v < VersionTLS13 {
+				c.sendAlert(alertProtocolVersion)
+				return errors.New("tls: client offered TLS version older than TLS 1.3")
+			}
+		}
+		// RFC 9001 Section 8.2.
 		if hs.clientHello.quicTransportParameters == nil {
-			// RFC 9001 Section 8.2.
 			c.sendAlert(alertMissingExtension)
 			return errors.New("tls: client did not send a quic_transport_parameters extension")
 		}