Update the TLS cipher string and provide configurability for TLS on outgoing federation (#5550)

1 files changed, 33 insertions, 6 deletions

diff --git a/synapse/crypto/context_factory.py b/synapse/crypto/context_factory.py
index 2bc5cc3807..4f48e8e88d 100644
--- a/synapse/crypto/context_factory.py
+++ b/synapse/crypto/context_factory.py
@@ -24,12 +24,25 @@ from OpenSSL import SSL, crypto
 from twisted.internet._sslverify import _defaultCurveName
 from twisted.internet.abstract import isIPAddress, isIPv6Address
 from twisted.internet.interfaces import IOpenSSLClientConnectionCreator
-from twisted.internet.ssl import CertificateOptions, ContextFactory, platformTrust
+from twisted.internet.ssl import (
+    CertificateOptions,
+    ContextFactory,
+    TLSVersion,
+    platformTrust,
+)
 from twisted.python.failure import Failure
 
 logger = logging.getLogger(__name__)
 
 
+_TLS_VERSION_MAP = {
+    "1": TLSVersion.TLSv1_0,
+    "1.1": TLSVersion.TLSv1_1,
+    "1.2": TLSVersion.TLSv1_2,
+    "1.3": TLSVersion.TLSv1_3,
+}
+
+
 class ServerContextFactory(ContextFactory):
     """Factory for PyOpenSSL SSL contexts that are used to handle incoming
     connections."""
@@ -43,16 +56,18 @@ class ServerContextFactory(ContextFactory):
         try:
             _ecCurve = crypto.get_elliptic_curve(_defaultCurveName)
             context.set_tmp_ecdh(_ecCurve)
-
         except Exception:
             logger.exception("Failed to enable elliptic curve for TLS")
-        context.set_options(SSL.OP_NO_SSLv2 | SSL.OP_NO_SSLv3)
+
+        context.set_options(
+            SSL.OP_NO_SSLv2 | SSL.OP_NO_SSLv3 | SSL.OP_NO_TLSv1 | SSL.OP_NO_TLSv1_1
+        )
         context.use_certificate_chain_file(config.tls_certificate_file)
         context.use_privatekey(config.tls_private_key)
 
         # https://hynek.me/articles/hardening-your-web-servers-ssl-ciphers/
         context.set_cipher_list(
-            "ECDH+AESGCM:ECDH+CHACHA20:ECDH+AES256:ECDH+AES128:!aNULL:!SHA1"
+            "ECDH+AESGCM:ECDH+CHACHA20:ECDH+AES256:ECDH+AES128:!aNULL:!SHA1:!AESCCM"
         )
 
     def getContext(self):
@@ -79,10 +94,22 @@ class ClientTLSOptionsFactory(object):
             # Use CA root certs provided by OpenSSL
             trust_root = platformTrust()
 
-        self._verify_ssl_context = CertificateOptions(trustRoot=trust_root).getContext()
+        # "insecurelyLowerMinimumTo" is the argument that will go lower than
+        # Twisted's default, which is why it is marked as "insecure" (since
+        # Twisted's defaults are reasonably secure). But, since Twisted is
+        # moving to TLS 1.2 by default, we want to respect the config option if
+        # it is set to 1.0 (which the alternate option, raiseMinimumTo, will not
+        # let us do).
+        minTLS = _TLS_VERSION_MAP[config.federation_client_minimum_tls_version]
+
+        self._verify_ssl = CertificateOptions(
+            trustRoot=trust_root, insecurelyLowerMinimumTo=minTLS
+        )
+        self._verify_ssl_context = self._verify_ssl.getContext()
         self._verify_ssl_context.set_info_callback(self._context_info_cb)
 
-        self._no_verify_ssl_context = CertificateOptions().getContext()
+        self._no_verify_ssl = CertificateOptions(insecurelyLowerMinimumTo=minTLS)
+        self._no_verify_ssl_context = self._no_verify_ssl.getContext()
         self._no_verify_ssl_context.set_info_callback(self._context_info_cb)
 
     def get_options(self, host):