/proc/tty/driver/serial in Linux 2.4.x reveals the exact number of characters used in serial links, which could allow local users to obtain potentially sensitive information such as the length of passwords.
A patch for shadow-utils 20000902 causes the useradd command to create a mail spool files with read/write privileges of the new user's group (mode 660), which allows other users in the same group to read or modify the new user's incoming email.