Endohydrolysis of (1->4)-beta-D-glucosidic linkages in cellulose, lichenin and cereal beta-D-glucans. By cellulosic materials and hemicelluloses. Will also hydrolyze 1,4-linkages in beta-D-glucans also containing 1,3-linkages. Belongs to the glycosyl hydrolase 12 (cellulase H) family.