A missing permission check in Jenkins PAM Authentication Plugin 1.5 and earlier, except 1.4.1 in PamSecurityRealm.DescriptorImpl#doTest allowed users with Overall/Read permission to obtain limited information about the file /etc/shadow and the user Jenkins is running as.
https://github.com/advisories/GHSA-xqwq-jxjh-wj82
https://jenkins.io/security/advisory/2019-05-21/#SECURITY-1316