1 files changed, 16 insertions, 9 deletions
diff --git a/synapse/crypto/event_signing.py b/synapse/crypto/event_signing.py
index ec7711ba7d..8774b28967 100644
--- a/synapse/crypto/event_signing.py
+++ b/synapse/crypto/event_signing.py
@@ -15,15 +15,15 @@
 # limitations under the License.
 
 
-from synapse.api.errors import SynapseError, Codes
-from synapse.events.utils import prune_event
+import hashlib
+import logging
 
 from canonicaljson import encode_canonical_json
-from unpaddedbase64 import encode_base64, decode_base64
 from signedjson.sign import sign_json
+from unpaddedbase64 import decode_base64, encode_base64
 
-import hashlib
-import logging
+from synapse.api.errors import Codes, SynapseError
+from synapse.events.utils import prune_event
 
 logger = logging.getLogger(__name__)
 
@@ -32,18 +32,25 @@ def check_event_content_hash(event, hash_algorithm=hashlib.sha256):
     """Check whether the hash for this PDU matches the contents"""
     name, expected_hash = compute_content_hash(event, hash_algorithm)
     logger.debug("Expecting hash: %s", encode_base64(expected_hash))
-    if name not in event.hashes:
+
+    # some malformed events lack a 'hashes'. Protect against it being missing
+    # or a weird type by basically treating it the same as an unhashed event.
+    hashes = event.get("hashes")
+    if not isinstance(hashes, dict):
+        raise SynapseError(400, "Malformed 'hashes'", Codes.UNAUTHORIZED)
+
+    if name not in hashes:
         raise SynapseError(
             400,
             "Algorithm %s not in hashes %s" % (
-                name, list(event.hashes),
+                name, list(hashes),
             ),
             Codes.UNAUTHORIZED,
         )
-    message_hash_base64 = event.hashes[name]
+    message_hash_base64 = hashes[name]
     try:
         message_hash_bytes = decode_base64(message_hash_base64)
-    except:
+    except Exception:
         raise SynapseError(
             400,
             "Invalid base64: %s" % (message_hash_base64,),