If you are upgrading from a version prior to 2.6.0, make sure to go through all the release notes available here.
#3831: XSS injection in object lists (ZSL-2015-5266)
#3835: CRSF Issues on Centreon (ZSL-2015-5263)
#3821: Upgrade from 2.6.1 to 2.6.3 kill Centreon Frontend
#3826: Split Component and zoom doesn’t work
#3827: Service Group Details page isn’t displayed for non admin in Centreon 2.6.3
#3837: Relation of passive service with SNMP traps problem with multihost link
#3842: Full logs display on event logs page for a non admin user