rbash in Bash before 4.4-beta2 did not prevent the shell user from modifying BASH_CMDS, thus allowing the user to execute any command with the permissions of the shell.
git.savannah.gnu.org/cgit/bash.git/tree/CHANGES?h=bash-4.4-testing#n65
lists.opensuse.org/opensuse-security-announce/2019-04/msg00049.html
bugs.launchpad.net/ubuntu/+source/bash/+bug/1803441
lists.debian.org/debian-lts-announce/2019/03/msg00028.html
security.netapp.com/advisory/ntap-20190411-0001/
usn.ubuntu.com/4058-1/
usn.ubuntu.com/4058-2/