Add verify server hostname to tls default

.changelog/17155.txt

@@ -0,0 +1,3 @@
+```release-note:improvement
+config: Add new `tls.defaults.verify_server_hostname` configuration option. This specifies the default value for any interfaces that support the `verify_server_hostname` option.
+```

agent/config/builder.go

@@ -2653,10 +2653,10 @@ func (b *builder) buildTLSConfig(rt RuntimeConfig, t TLS) (tlsutil.Config, error
 		return c, errors.New("verify_outgoing is not valid in the tls.grpc stanza")
 	}
 
-	// Similarly, only the internal RPC configuration honors VerifyServerHostname
+	// Similarly, only the internal RPC and defaults configuration honor VerifyServerHostname
 	// so we call it out here too.
-	if t.Defaults.VerifyServerHostname != nil || t.GRPC.VerifyServerHostname != nil || t.HTTPS.VerifyServerHostname != nil {
-		return c, errors.New("verify_server_hostname is only valid in the tls.internal_rpc stanza")
+	if t.GRPC.VerifyServerHostname != nil || t.HTTPS.VerifyServerHostname != nil {
+		return c, errors.New("verify_server_hostname is only valid in the tls.defaults and tls.internal_rpc stanzas")
 	}
 
 	// And UseAutoCert right now only applies to external gRPC interface.
@@ -2706,8 +2706,11 @@ func (b *builder) buildTLSConfig(rt RuntimeConfig, t TLS) (tlsutil.Config, error
 	}
 
 	mapCommon("internal_rpc", t.InternalRPC, &c.InternalRPC)
-	c.InternalRPC.VerifyServerHostname = boolVal(t.InternalRPC.VerifyServerHostname)
 
+	c.InternalRPC.VerifyServerHostname = boolVal(t.Defaults.VerifyServerHostname)
+	if t.InternalRPC.VerifyServerHostname != nil {
+		c.InternalRPC.VerifyServerHostname = boolVal(t.InternalRPC.VerifyServerHostname)
+	}
 	// Setting only verify_server_hostname is documented to imply verify_outgoing.
 	// If it doesn't then we risk sending communication over plain TCP when we
 	// documented it as forcing TLS for RPCs. Enforce this here rather than in

agent/config/runtime_test.go

@@ -2736,7 +2736,44 @@ func TestLoad_IntegrationWithFlags(t *testing.T) {
 				}
 			}
 		`},
-		expectedErr: "verify_server_hostname is only valid in the tls.internal_rpc stanza",
+		expected: func(rt *RuntimeConfig) {
+			rt.DataDir = dataDir
+			rt.TLS.InternalRPC.VerifyServerHostname = true
+			rt.TLS.InternalRPC.VerifyOutgoing = true
+		},
+	})
+	run(t, testCase{
+		desc: "verify_server_hostname in the defaults stanza and internal_rpc",
+		args: []string{
+			`-data-dir=` + dataDir,
+		},
+		hcl: []string{`
+			tls {
+				defaults {
+					verify_server_hostname = false
+				},
+				internal_rpc {
+					verify_server_hostname = true
+				}
+			}
+		`},
+		json: []string{`
+			{
+				"tls": {
+					"defaults": {
+						"verify_server_hostname": false
+					},
+					"internal_rpc": {
+						"verify_server_hostname": true
+					}
+				}
+			}
+		`},
+		expected: func(rt *RuntimeConfig) {
+			rt.DataDir = dataDir
+			rt.TLS.InternalRPC.VerifyServerHostname = true
+			rt.TLS.InternalRPC.VerifyOutgoing = true
+		},
 	})
 	run(t, testCase{
 		desc: "verify_server_hostname in the grpc stanza",
@@ -2759,7 +2796,7 @@ func TestLoad_IntegrationWithFlags(t *testing.T) {
 				}
 			}
 		`},
-		expectedErr: "verify_server_hostname is only valid in the tls.internal_rpc stanza",
+		expectedErr: "verify_server_hostname is only valid in the tls.defaults and tls.internal_rpc stanza",
 	})
 	run(t, testCase{
 		desc: "verify_server_hostname in the https stanza",
@@ -2782,7 +2819,7 @@ func TestLoad_IntegrationWithFlags(t *testing.T) {
 				}
 			}
 		`},
-		expectedErr: "verify_server_hostname is only valid in the tls.internal_rpc stanza",
+		expectedErr: "verify_server_hostname is only valid in the tls.defaults and tls.internal_rpc stanza",
 	})
 	run(t, testCase{
 		desc: "translated keys",
@@ -5723,6 +5760,74 @@ func TestLoad_IntegrationWithFlags(t *testing.T) {
 			rt.TLS.InternalRPC.VerifyOutgoing = true
 		},
 	})
+	run(t, testCase{
+		desc: "tls.defaults.verify_server_hostname implies tls.internal_rpc.verify_outgoing",
+		args: []string{
+			`-data-dir=` + dataDir,
+		},
+		json: []string{`
+			{
+				"tls": {
+					"defaults": {
+						"verify_server_hostname": true
+					}
+				}
+			}
+		`},
+		hcl: []string{`
+			tls {
+				defaults {
+					verify_server_hostname = true
+				}
+			}
+		`},
+		expected: func(rt *RuntimeConfig) {
+			rt.DataDir = dataDir
+
+			rt.TLS.Domain = "consul."
+			rt.TLS.NodeName = "thehostname"
+
+			rt.TLS.InternalRPC.VerifyServerHostname = true
+			rt.TLS.InternalRPC.VerifyOutgoing = true
+		},
+	})
+	run(t, testCase{
+		desc: "tls.internal_rpc.verify_server_hostname overwrites tls.defaults.verify_server_hostname",
+		args: []string{
+			`-data-dir=` + dataDir,
+		},
+		json: []string{`
+			{
+				"tls": {
+					"defaults": {
+						"verify_server_hostname": false
+					},
+					"internal_rpc": {
+						"verify_server_hostname": true
+					}
+				}
+			}
+		`},
+		hcl: []string{`
+			tls {
+				defaults {
+					verify_server_hostname = false
+				},
+				internal_rpc {
+					verify_server_hostname = true
+				}
+			}
+		`},
+		expected: func(rt *RuntimeConfig) {
+			rt.DataDir = dataDir
+
+			rt.TLS.Domain = "consul."
+			rt.TLS.NodeName = "thehostname"
+
+			rt.TLS.InternalRPC.VerifyServerHostname = true
+			rt.TLS.InternalRPC.VerifyOutgoing = true
+		},
+	})
 	run(t, testCase{
 		desc: "tls.grpc.use_auto_cert defaults to false",
 		args: []string{

website/content/docs/agent/config/config-files.mdx

@@ -2094,6 +2094,12 @@ specially crafted certificate signed by the CA can be used to gain full access t
       * `TLSv1_2` (default)
       * `TLSv1_3`
 
+    - `verify_server_hostname` ((#tls_internal_rpc_verify_server_hostname)) When 
+      set to true, Consul verifies the TLS certificate presented by the servers 
+      match the hostname `server.<datacenter>.<domain>`. By default this is false, 
+      and Consul does not verify the hostname of the certificate, only that it 
+      is signed by a trusted CA. 
+
       **WARNING: TLS 1.1 and lower are generally considered less secure and
       should not be used if possible.**
 
@@ -2201,7 +2207,7 @@ specially crafted certificate signed by the CA can be used to gain full access t
       only way to enforce that no client can communicate with a server unencrypted
       is to also enable `verify_incoming` which requires client certificates too.
 
-    - `verify_server_hostname` ((#tls_internal_rpc_verify_server_hostname)) When
+    - `verify_server_hostname` Overrides [tls.defaults.verify_server_hostname](#tls_defaults_verify_server_hostname). When
       set to true, Consul verifies the TLS certificate presented by the servers
       match the hostname `server.<datacenter>.<domain>`. By default this is false,
       and Consul does not verify the hostname of the certificate, only that it
@@ -2285,9 +2291,6 @@ tls {
     ca_file = "/etc/pki/tls/certs/ca-bundle.crt"
     verify_incoming = true
     verify_outgoing = true
-  }
-
-  internal_rpc {
     verify_server_hostname = true
   }
 }
@@ -2316,9 +2319,7 @@ tls {
       "cert_file": "/etc/pki/tls/certs/my.crt",
       "ca_file": "/etc/pki/tls/certs/ca-bundle.crt",
       "verify_incoming": true,
-      "verify_outgoing": true
-    },
-    "internal_rpc": {
+      "verify_outgoing": true,
       "verify_server_hostname": true
     }
   }

website/content/docs/agent/index.mdx

@@ -276,9 +276,6 @@ tls {
     ca_file = "/consul/config/certs/consul-agent-ca.pem"
     cert_file = "/consul/config/certs/dc1-server-consul-0.pem"
     key_file = "/consul/config/certs/dc1-server-consul-0-key.pem"
-  }
-
-  internal_rpc {
     verify_server_hostname = true
   }
 }

website/content/docs/security/security-models/core.mdx

@@ -128,9 +128,6 @@ environment and adapt these configurations accordingly.
         ca_file = "consul-agent-ca.pem"
         cert_file = "dc1-server-consul-0.pem"
         key_file = "dc1-server-consul-0-key.pem"
-      }
-
-      internal_rpc {
         verify_server_hostname = true
       }
     }
@@ -148,9 +145,6 @@ environment and adapt these configurations accordingly.
           verify_incoming = false
           verify_outgoing = true
           ca_file = "consul-agent-ca.pem"
-        }
-
-        internal_rpc {
           verify_server_hostname = true
         }
       }