The REST interface in Cisco Spark 2015-06 allows remote attackers to cause a denial of service (resource outage) by accessing an administrative page, aka Bug ID CSCuv84125.
https://euvd.enisa.europa.eu/vulnerability/EUVD-2016-2423
http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20160210-sp3