Bash before 4.4 allows local users to execute arbitrary commands with root privileges via crafted SHELLOPTS and PS4 environment variables.
http://rhn.redhat.com/errata/RHSA-2017-0725.html
https://access.redhat.com/errata/RHSA-2017:1931
https://h20566.www2.hpe.com/portal/site/hpsc/public/kb/docDisplay?docId=emr_na-c05388115
https://lists.gnu.org/archive/html/bug-bash/2016-09/msg00018.html
https://security.gentoo.org/glsa/201701-02