Session fixation vulnerability in Jenkins before 1.551 and LTS before 1.532.2 allows remote attackers to hijack web sessions via vectors involving the "override" of Jenkins cookies.
https://wiki.jenkins-ci.org/display/SECURITY/Jenkins+Security+Advisory+2014-02-14
https://github.com/jenkinsci/jenkins/commit/8ac74c350779921598f9d5edfed39dd35de8842a