Hydrolyzes cellohexaose to a mixture of cellotetraose, cellotriose and cellobiose, with only a trace of glucose. It hydrolyzed cellopentaose to cellotriose and cellobiose, and cellotetraose to cellobiose, but it did not hydrolyze cellotriose. Has also weak endoglucanase activity. Hydrolyzes glucosidic bonds with inversion of anomeric configuration. Hydrolysis of (1->4)-beta-D-glucosidic linkages in cellulose and cellotetraose, releasing cellobiose from the non-reducing ends of the chains. Belongs to the glycosyl hydrolase 48 (cellulase L) family.