A improper authentication vulnerability exists in Jenkins 2.137 and earlier, 2.121.2 and earlier in SecurityRealm.java, TokenBasedRememberMeServices2.java that allows attackers with a valid cookie to remain logged in even if that feature is disabled.
https://github.com/advisories/GHSA-q4cq-r7hg-pxqq
https://jenkins.io/security/advisory/2018-08-15/#SECURITY-996