Add restrictions by default to open registration in Synapse (#12091)

2 files changed, 30 insertions, 1 deletions

diff --git a/synapse/app/homeserver.py b/synapse/app/homeserver.py
index ad2b7c9515..0f75e7b9d4 100644
--- a/synapse/app/homeserver.py
+++ b/synapse/app/homeserver.py
@@ -351,6 +351,23 @@ def setup(config_options: List[str]) -> SynapseHomeServer:
     if config.server.gc_seconds:
         synapse.metrics.MIN_TIME_BETWEEN_GCS = config.server.gc_seconds
 
+    if (
+        config.registration.enable_registration
+        and not config.registration.enable_registration_without_verification
+    ):
+        if (
+            not config.captcha.enable_registration_captcha
+            and not config.registration.registrations_require_3pid
+            and not config.registration.registration_requires_token
+        ):
+
+            raise ConfigError(
+                "You have enabled open registration without any verification. This is a known vector for "
+                "spam and abuse. If you would like to allow public registration, please consider adding email, "
+                "captcha, or token-based verification. Otherwise this check can be removed by setting the "
+                "`enable_registration_without_verification` config option to `true`."
+            )
+
     hs = SynapseHomeServer(
         config.server.server_name,
         config=config,
diff --git a/synapse/config/registration.py b/synapse/config/registration.py
index ea9b50fe97..40fb329a7f 100644
--- a/synapse/config/registration.py
+++ b/synapse/config/registration.py
@@ -33,6 +33,10 @@ class RegistrationConfig(Config):
                 str(config["disable_registration"])
             )
 
+        self.enable_registration_without_verification = strtobool(
+            str(config.get("enable_registration_without_verification", False))
+        )
+
         self.registrations_require_3pid = config.get("registrations_require_3pid", [])
         self.allowed_local_3pids = config.get("allowed_local_3pids", [])
         self.enable_3pid_lookup = config.get("enable_3pid_lookup", True)
@@ -207,10 +211,18 @@ class RegistrationConfig(Config):
         # Registration can be rate-limited using the parameters in the "Ratelimiting"
         # section of this file.
 
-        # Enable registration for new users.
+        # Enable registration for new users. Defaults to 'false'. It is highly recommended that if you enable registration,
+        # you use either captcha, email, or token-based verification to verify that new users are not bots. In order to enable registration
+        # without any verification, you must also set `enable_registration_without_verification`, found below.
         #
         #enable_registration: false
 
+        # Enable registration without email or captcha verification. Note: this option is *not* recommended,
+        # as registration without verification is a known vector for spam and abuse. Defaults to false. Has no effect
+        # unless `enable_registration` is also enabled.
+        #
+        #enable_registration_without_verification: true
+
         # Time that a user's session remains valid for, after they log in.
         #
         # Note that this is not currently compatible with guest logins.