Jenkins before 2.3 and LTS before 1.651.2 allows remote authenticated users to trigger updating of update site metadata by leveraging a missing permissions check. NOTE: this issue can be combined with DNS cache poisoning to cause a denial of service (service disruption).
https://www.cloudbees.com/jenkins-security-advisory-2016-05-11
https://wiki.jenkins-ci.org/display/SECURITY/Jenkins+Security+Advisory+2016-05-11