swaps: more robust parsing

electrum/plugins/nwc/nwcserver.py

@@ -333,8 +333,12 @@ class NWCServer(Logger, EventListener):
             try:
                 content = our_connection_secret.decrypt_message(event.content, event.pubkey)
                 content = json.loads(content)
+                if not isinstance(content, dict):
+                    raise Exception("malformed content, not dict")
                 event.content = content
                 params: dict = content['params']
+                if not isinstance(params, dict):
+                    raise Exception("malformed params, not dict")
             except Exception:
                 self.logger.debug(f"Invalid request event content: {event.content}", exc_info=True)
                 continue

electrum/plugins/psbt_nostr/psbt_nostr.py

@@ -210,6 +210,8 @@ class CosignerWallet(Logger):
                     continue
                 try:
                     message = json_decode(message)
+                    if not isinstance(message, dict):
+                        raise Exception("malformed message, not dict")
                     tx_hex = message.get('tx')
                     label = message.get('label', '')
                     tx = tx_from_any(tx_hex)