diff --git a/synapse/push/emailpusher.py b/synapse/push/emailpusher.py
index cd89b54305..99a18874d1 100644
--- a/synapse/push/emailpusher.py
+++ b/synapse/push/emailpusher.py
@@ -19,8 +19,9 @@ from twisted.internet.error import AlreadyCalled, AlreadyCancelled
from twisted.internet.interfaces import IDelayedCall
from synapse.metrics.background_process_metrics import run_as_background_process
-from synapse.push import Pusher, PusherConfig, ThrottleParams
+from synapse.push import Pusher, PusherConfig, PusherConfigException, ThrottleParams
from synapse.push.mailer import Mailer
+from synapse.util.threepids import validate_email
if TYPE_CHECKING:
from synapse.server import HomeServer
@@ -71,6 +72,12 @@ class EmailPusher(Pusher):
self._is_processing = False
+ # Make sure that the email is valid.
+ try:
+ validate_email(self.email)
+ except ValueError:
+ raise PusherConfigException("Invalid email")
+
def on_started(self, should_check_for_notifs: bool) -> None:
"""Called when this pusher has been started.
diff --git a/synapse/rest/client/v2_alpha/account.py b/synapse/rest/client/v2_alpha/account.py
index 3aad15132d..085561d3e9 100644
--- a/synapse/rest/client/v2_alpha/account.py
+++ b/synapse/rest/client/v2_alpha/account.py
@@ -39,7 +39,7 @@ from synapse.metrics import threepid_send_requests
from synapse.push.mailer import Mailer
from synapse.util.msisdn import phone_number_to_msisdn
from synapse.util.stringutils import assert_valid_client_secret, random_string
-from synapse.util.threepids import canonicalise_email, check_3pid_allowed
+from synapse.util.threepids import check_3pid_allowed, validate_email
from ._base import client_patterns, interactive_auth_handler
@@ -92,7 +92,7 @@ class EmailPasswordRequestTokenRestServlet(RestServlet):
# Stored in the database "foo@bar.com"
# User requests with "FOO@bar.com" would raise a Not Found error
try:
- email = canonicalise_email(body["email"])
+ email = validate_email(body["email"])
except ValueError as e:
raise SynapseError(400, str(e))
send_attempt = body["send_attempt"]
@@ -247,7 +247,7 @@ class PasswordRestServlet(RestServlet):
# We store all email addresses canonicalised in the DB.
# (See add_threepid in synapse/handlers/auth.py)
try:
- threepid["address"] = canonicalise_email(threepid["address"])
+ threepid["address"] = validate_email(threepid["address"])
except ValueError as e:
raise SynapseError(400, str(e))
# if using email, we must know about the email they're authing with!
@@ -375,7 +375,7 @@ class EmailThreepidRequestTokenRestServlet(RestServlet):
# Otherwise the email will be sent to "FOO@bar.com" and stored as
# "foo@bar.com" in database.
try:
- email = canonicalise_email(body["email"])
+ email = validate_email(body["email"])
except ValueError as e:
raise SynapseError(400, str(e))
send_attempt = body["send_attempt"]
diff --git a/synapse/rest/client/v2_alpha/register.py b/synapse/rest/client/v2_alpha/register.py
index c5a6800b8a..a30a5df1b1 100644
--- a/synapse/rest/client/v2_alpha/register.py
+++ b/synapse/rest/client/v2_alpha/register.py
@@ -49,7 +49,11 @@ from synapse.push.mailer import Mailer
from synapse.util.msisdn import phone_number_to_msisdn
from synapse.util.ratelimitutils import FederationRateLimiter
from synapse.util.stringutils import assert_valid_client_secret, random_string
-from synapse.util.threepids import canonicalise_email, check_3pid_allowed
+from synapse.util.threepids import (
+ canonicalise_email,
+ check_3pid_allowed,
+ validate_email,
+)
from ._base import client_patterns, interactive_auth_handler
@@ -111,7 +115,7 @@ class EmailRegisterRequestTokenRestServlet(RestServlet):
# (See on_POST in EmailThreepidRequestTokenRestServlet
# in synapse/rest/client/v2_alpha/account.py)
try:
- email = canonicalise_email(body["email"])
+ email = validate_email(body["email"])
except ValueError as e:
raise SynapseError(400, str(e))
send_attempt = body["send_attempt"]
diff --git a/synapse/util/threepids.py b/synapse/util/threepids.py
index 281c5be4fb..a1cf1960b0 100644
--- a/synapse/util/threepids.py
+++ b/synapse/util/threepids.py
@@ -18,6 +18,16 @@ import re
logger = logging.getLogger(__name__)
+# it's unclear what the maximum length of an email address is. RFC3696 (as corrected
+# by errata) says:
+# the upper limit on address lengths should normally be considered to be 254.
+#
+# In practice, mail servers appear to be more tolerant and allow 400 characters
+# or so. Let's allow 500, which should be plenty for everyone.
+#
+MAX_EMAIL_ADDRESS_LENGTH = 500
+
+
def check_3pid_allowed(hs, medium, address):
"""Checks whether a given format of 3PID is allowed to be used on this HS
@@ -70,3 +80,23 @@ def canonicalise_email(address: str) -> str:
raise ValueError("Unable to parse email address")
return parts[0].casefold() + "@" + parts[1].lower()
+
+
+def validate_email(address: str) -> str:
+ """Does some basic validation on an email address.
+
+ Returns the canonicalised email, as returned by `canonicalise_email`.
+
+ Raises a ValueError if the email is invalid.
+ """
+ # First we try canonicalising in case that fails
+ address = canonicalise_email(address)
+
+ # Email addresses have to be at least 3 characters.
+ if len(address) < 3:
+ raise ValueError("Unable to parse email address")
+
+ if len(address) > MAX_EMAIL_ADDRESS_LENGTH:
+ raise ValueError("Unable to parse email address")
+
+ return address
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