Print warning when 'tls_cipher_suites' includes only blacklisted cipher suites

command/server/listener.go

@@ -16,6 +16,7 @@ import (
 	"github.com/hashicorp/vault/helper/proxyutil"
 	"github.com/hashicorp/vault/helper/reload"
 	"github.com/hashicorp/vault/helper/tlsutil"
+	"github.com/jefferai/isbadcipher"
 	"github.com/mitchellh/cli"
 )
 
@@ -140,6 +141,34 @@ PASSPHRASECORRECT:
 		if err != nil {
 			return nil, nil, nil, errwrap.Wrapf("invalid value for 'tls_cipher_suites': {{err}}", err)
 		}
+
+		// HTTP/2 with TLS 1.2 blacklists several cipher suites.
+		// https://tools.ietf.org/html/rfc7540#appendix-A
+		//
+		// Since the CLI (net/http) automatically uses HTTP/2 with TLS 1.2,
+		// we check here if all or some specified cipher suites are blacklisted.
+		badCiphers := []string{}
+		for _, cipher := range ciphers {
+			if isbadcipher.IsBadCipher(cipher) {
+				// Get the name of the current cipher.
+				cipherStr, err := tlsutil.GetCipherName(cipher)
+				if err != nil {
+					return nil, nil, nil, errwrap.Wrapf("invalid value for 'tls_cipher_suites': {{err}}", err)
+				}
+				badCiphers = append(badCiphers, cipherStr)
+			}
+		}
+		if len(badCiphers) == len(ciphers) {
+			ui.Warn(`WARNING! All cipher suites defined by 'tls_cipher_suites' are blacklisted by the
+HTTP/2 specification. HTTP/2 communication with TLS 1.2 will not work as intended
+and Vault will be unavailable via the CLI.
+Please see https://tools.ietf.org/html/rfc7540#appendix-A for further information.`)
+		} else if len(badCiphers) > 0 {
+			ui.Warn(fmt.Sprintf(`WARNING! The following cipher suites defined by 'tls_cipher_suites' are 
+blacklisted by the HTTP/2 specification: 
+%v
+Please see https://tools.ietf.org/html/rfc7540#appendix-A for further information.`, badCiphers))
+		}
 		tlsConf.CipherSuites = ciphers
 	}
 	if v, ok := config["tls_prefer_server_cipher_suites"]; ok {

helper/tlsutil/tlsutil.go

@@ -14,34 +14,36 @@ var TLSLookup = map[string]uint16{
 	"tls12": tls.VersionTLS12,
 }
 
+// cipherMap maps the cipher suite names to the internal cipher suite code.
+var cipherMap = map[string]uint16{
+	"TLS_RSA_WITH_RC4_128_SHA":                tls.TLS_RSA_WITH_RC4_128_SHA,
+	"TLS_RSA_WITH_3DES_EDE_CBC_SHA":           tls.TLS_RSA_WITH_3DES_EDE_CBC_SHA,
+	"TLS_RSA_WITH_AES_128_CBC_SHA":            tls.TLS_RSA_WITH_AES_128_CBC_SHA,
+	"TLS_RSA_WITH_AES_256_CBC_SHA":            tls.TLS_RSA_WITH_AES_256_CBC_SHA,
+	"TLS_RSA_WITH_AES_128_CBC_SHA256":         tls.TLS_RSA_WITH_AES_128_CBC_SHA256,
+	"TLS_RSA_WITH_AES_128_GCM_SHA256":         tls.TLS_RSA_WITH_AES_128_GCM_SHA256,
+	"TLS_RSA_WITH_AES_256_GCM_SHA384":         tls.TLS_RSA_WITH_AES_256_GCM_SHA384,
+	"TLS_ECDHE_ECDSA_WITH_RC4_128_SHA":        tls.TLS_ECDHE_ECDSA_WITH_RC4_128_SHA,
+	"TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA":    tls.TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA,
+	"TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA":    tls.TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA,
+	"TLS_ECDHE_RSA_WITH_RC4_128_SHA":          tls.TLS_ECDHE_RSA_WITH_RC4_128_SHA,
+	"TLS_ECDHE_RSA_WITH_3DES_EDE_CBC_SHA":     tls.TLS_ECDHE_RSA_WITH_3DES_EDE_CBC_SHA,
+	"TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA":      tls.TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA,
+	"TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA":      tls.TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA,
+	"TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA256": tls.TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA256,
+	"TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256":   tls.TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256,
+	"TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256":   tls.TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256,
+	"TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256": tls.TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256,
+	"TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384":   tls.TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384,
+	"TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384": tls.TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384,
+	"TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305":    tls.TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305,
+	"TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305":  tls.TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305,
+}
+
 // ParseCiphers parse ciphersuites from the comma-separated string into recognized slice
 func ParseCiphers(cipherStr string) ([]uint16, error) {
 	suites := []uint16{}
 	ciphers := strutil.ParseStringSlice(cipherStr, ",")
-	cipherMap := map[string]uint16{
-		"TLS_RSA_WITH_RC4_128_SHA":                tls.TLS_RSA_WITH_RC4_128_SHA,
-		"TLS_RSA_WITH_3DES_EDE_CBC_SHA":           tls.TLS_RSA_WITH_3DES_EDE_CBC_SHA,
-		"TLS_RSA_WITH_AES_128_CBC_SHA":            tls.TLS_RSA_WITH_AES_128_CBC_SHA,
-		"TLS_RSA_WITH_AES_256_CBC_SHA":            tls.TLS_RSA_WITH_AES_256_CBC_SHA,
-		"TLS_RSA_WITH_AES_128_CBC_SHA256":         tls.TLS_RSA_WITH_AES_128_CBC_SHA256,
-		"TLS_RSA_WITH_AES_128_GCM_SHA256":         tls.TLS_RSA_WITH_AES_128_GCM_SHA256,
-		"TLS_RSA_WITH_AES_256_GCM_SHA384":         tls.TLS_RSA_WITH_AES_256_GCM_SHA384,
-		"TLS_ECDHE_ECDSA_WITH_RC4_128_SHA":        tls.TLS_ECDHE_ECDSA_WITH_RC4_128_SHA,
-		"TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA":    tls.TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA,
-		"TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA":    tls.TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA,
-		"TLS_ECDHE_RSA_WITH_RC4_128_SHA":          tls.TLS_ECDHE_RSA_WITH_RC4_128_SHA,
-		"TLS_ECDHE_RSA_WITH_3DES_EDE_CBC_SHA":     tls.TLS_ECDHE_RSA_WITH_3DES_EDE_CBC_SHA,
-		"TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA":      tls.TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA,
-		"TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA":      tls.TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA,
-		"TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA256": tls.TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA256,
-		"TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256":   tls.TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256,
-		"TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256":   tls.TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256,
-		"TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256": tls.TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256,
-		"TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384":   tls.TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384,
-		"TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384": tls.TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384,
-		"TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305":    tls.TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305,
-		"TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305":  tls.TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305,
-	}
 	for _, cipher := range ciphers {
 		if v, ok := cipherMap[cipher]; ok {
 			suites = append(suites, v)
@@ -52,3 +54,14 @@ func ParseCiphers(cipherStr string) ([]uint16, error) {
 
 	return suites, nil
 }
+
+// GetCipherName returns the name of a given cipher suite code or an error if the
+// given cipher is unsupported.
+func GetCipherName(cipher uint16) (string, error) {
+	for cipherStr, cipherCode := range cipherMap {
+		if cipherCode == cipher {
+			return cipherStr, nil
+		}
+	}
+	return "", fmt.Errorf("unsupported cipher %d", cipher)
+}

helper/tlsutil/tlsutil_test.go

@@ -28,3 +28,21 @@ func TestParseCiphers(t *testing.T) {
 		t.Fatal("cipher order is not preserved")
 	}
 }
+
+func TestGetCipherName(t *testing.T) {
+	testOkCipherStr := "TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA"
+	testOkCipher := tls.TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA
+	cipherStr, err := GetCipherName(testOkCipher)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if cipherStr != testOkCipherStr {
+		t.Fatalf("cipher string should be %s but is %s", testOkCipherStr, cipherStr)
+	}
+
+	var testBadCipher uint16 = 0xC022
+	cipherStr, err = GetCipherName(testBadCipher)
+	if err == nil {
+		t.Fatal("should fail on unsupported cipher 0xC022")
+	}
+}