Versions mentioned in the description apply to the upstream
Remediation section below for
Debian:9 relevant versions.
The Debian shadow package before 1:4.5-1 for Shadow incorrectly lists pts/0 and pts/1 as physical terminals in /etc/securetty. This allows local users to login as password-less users even if they are connected by non-physical means such as SSH (hence bypassing PAM's nullok_secure configuration). This notably affects environments such as virtual machines automatically generated with a default blank root password, allowing all local users to escalate privileges.
shadow to version 1:4.4-4.1+deb9u1 or higher.