You can get the spark version by using the following command:
spark-submit --version
spark-shell --version
spark-sql --version
You can visit the below site to know the spark-version used in CDH 5.7.0
http://www.cloudera.com/documentation/enterprise/release-notes/topics/cdh_rn_new_in_cdh_57.html#concept_m3k_rxh_1v