Validate that the unmarshaled RecordValue has valid field data

weed/mq/kafka/protocol/fetch.go

@@ -1146,6 +1146,13 @@ func (h *Handler) decodeRecordValueToKafkaMessage(topicName string, recordValueB
 		return recordValueBytes
 	}
 
+	// Validate that the unmarshaled RecordValue has valid field data
+	// Protobuf unmarshal is lenient and can succeed with garbage data for random bytes
+	// If Fields is nil or empty, this is not a valid RecordValue - return raw bytes
+	if recordValue.Fields == nil || len(recordValue.Fields) == 0 {
+		return recordValueBytes
+	}
+
 	// If schema management is enabled, re-encode the RecordValue to Confluent format
 	if h.IsSchemaEnabled() {
 		if encodedMsg, err := h.encodeRecordValueToConfluentFormat(topicName, recordValue); err == nil {