/bin/login in shadow 4.0.18.1 in Debian GNU/Linux, and probably other Linux distributions, allows local users in the utmp group to overwrite arbitrary files via a symlink attack on a temporary file referenced in a line (aka ut_line) field in a utmp entry.

useradd in shadow-utils before 4.0.3, and possibly other versions before 4.0.8, does not provide a required argument to the open function when creating a new user mailbox, which causes the mailbox to be created with unpredictable permissions and possibly allows attackers to read or modify the mailbox.

The Debian installer for the (1) shadow 4.0.14 and (2) base-config 2.53.10 packages includes sensitive information in world-readable log files, including preseeded passwords and pppoeconf passwords, which might allow local users to gain privileges.