From 4c289fc6ad3d7c2afa69e36cdf2cc9a172cb1c9c Mon Sep 17 00:00:00 2001
From: Matthew Holt <mholt@users.noreply.github.com>
Date: Tue, 17 Sep 2019 23:13:21 -0600
Subject: [PATCH] Allow domain fronting with TLS client auth if explicitly
configured
---
modules/caddyhttp/caddyhttp.go | 20 ++++++++++++--------
modules/caddyhttp/server.go | 4 ++--
2 files changed, 14 insertions(+), 10 deletions(-)
diff --git a/modules/caddyhttp/caddyhttp.go b/modules/caddyhttp/caddyhttp.go
index c044a9bfd..0a26ad181 100644
--- a/modules/caddyhttp/caddyhttp.go
+++ b/modules/caddyhttp/caddyhttp.go
@@ -78,16 +78,20 @@ func (app *App) Provision(ctx caddy.Context) error {
srv.AutoHTTPS = new(AutoHTTPSConfig)
}
- // disallow TLS client auth bypass which could
- // otherwise be exploited by sending an unprotected
- // SNI value during TLS handshake, then a protected
- // Host header during HTTP request later on that
- // connection
- if srv.hasTLSClientAuth() {
- srv.StrictSNIHost = true
+ // if not explicitly configured by the user, disallow TLS
+ // client auth bypass (domain fronting) which could
+ // otherwise be exploited by sending an unprotected SNI
+ // value during a TLS handshake, then putting a protected
+ // domain in the Host header after establishing connection;
+ // this is a safe default, but we allow users to override
+ // it for example in the case of running a proxy where
+ // domain fronting is desired and access is not restricted
+ // based on hostname
+ if srv.StrictSNIHost == nil && srv.hasTLSClientAuth() {
+ trueBool := true
+ srv.StrictSNIHost = &trueBool
}
- // TODO: Test this function to ensure these replacements are performed
for i := range srv.Listen {
srv.Listen[i] = repl.ReplaceAll(srv.Listen[i], "")
}
diff --git a/modules/caddyhttp/server.go b/modules/caddyhttp/server.go
index b4952e124..0ccdeea07 100644
--- a/modules/caddyhttp/server.go
+++ b/modules/caddyhttp/server.go
@@ -42,7 +42,7 @@ type Server struct {
TLSConnPolicies caddytls.ConnectionPolicies `json:"tls_connection_policies,omitempty"`
AutoHTTPS *AutoHTTPSConfig `json:"automatic_https,omitempty"`
MaxRehandles *int `json:"max_rehandles,omitempty"`
- StrictSNIHost bool `json:"strict_sni_host,omitempty"`
+ StrictSNIHost *bool `json:"strict_sni_host,omitempty"`
// This field is not subject to compatibility promises
ExperimentalHTTP3 bool `json:"experimental_http3,omitempty"`
@@ -164,7 +164,7 @@ func (s *Server) enforcementHandler(w http.ResponseWriter, r *http.Request, next
// servers that rely on TLS ClientAuth sharing a listener
// with servers that do not; if not enforced, client could
// bypass by sending benign SNI then restricted Host header
- if s.StrictSNIHost && r.TLS != nil {
+ if s.StrictSNIHost != nil && *s.StrictSNIHost && r.TLS != nil {
hostname, _, err := net.SplitHostPort(r.Host)
if err != nil {
hostname = r.Host // OK; probably lacked port