1 files changed, 11 insertions, 1 deletions
diff --git a/synapse/config/tls.py b/synapse/config/tls.py
index 81b3a659fe..9fcc79816d 100644
--- a/synapse/config/tls.py
+++ b/synapse/config/tls.py
@@ -64,10 +64,14 @@ class TlsConfig(Config):
         self.tls_certificate = None
         self.tls_private_key = None
 
-    def is_disk_cert_valid(self):
+    def is_disk_cert_valid(self, allow_self_signed=True):
         """
         Is the certificate we have on disk valid, and if so, for how long?
 
+        Args:
+            allow_self_signed (bool): Should we allow the certificate we
+                read to be self signed?
+
         Returns:
             int: Days remaining of certificate validity.
             None: No certificate exists.
@@ -88,6 +92,12 @@ class TlsConfig(Config):
             logger.exception("Failed to parse existing certificate off disk!")
             raise
 
+        if not allow_self_signed:
+            if tls_certificate.get_subject() == tls_certificate.get_issuer():
+                raise ValueError(
+                    "TLS Certificate is self signed, and this is not permitted"
+                )
+
         # YYYYMMDDhhmmssZ -- in UTC
         expires_on = datetime.strptime(
             tls_certificate.get_notAfter().decode('ascii'), "%Y%m%d%H%M%SZ"