The JIRA Workflow Designer Plugin in Atlassian JIRA Server before 6.3.0 improperly uses an XML parser and deserializer, which allows remote attackers to execute arbitrary code, read arbitrary files, or cause a denial of service via a crafted serialized Java object.
https://www.kb.cert.org/vuls/id/307983
https://jira.atlassian.com/browse/JRASERVER-64077
https://confluence.atlassian.com/jira063/jira-security-advisory-2017-03-09-875604401.html