Managing Systems and Workgroups: A Guide for HP-UX System Administrators

Administering a System: Managing System Security

Managing Access to Files and Directories

Chapter 8772

Protecting User Accounts

These guidelines should be followed to protect user accounts:

• Except for the owners, home directories should not be writable

because it allows any user to add and remove ﬁles from them.

• Users’ .profile, .kshrc, .login, and .cshrc ﬁles should not be

writable by anyone other than the account owner.

• A user’s .rhosts ﬁle should not be readable or writable by anybody

other than the owner. This precaution prevents users from guessing

what other accounts you have, as well as preventing anyone from

editing your .rhosts ﬁle to gain access to those systems. See

hosts.equiv (4).

• Use of a .netrc ﬁle is discouraged, since it bypasses login

authentication for remote login and even contains the user’s

unencrypted password. If used, .netrc must not be readable or

writable by anyone other than its owner. See netrc (4).

• Some systems maintain an /etc/securetty ﬁle, which should not be

writable. See login (1).

Security Considerations for Device Files

Access to all devices in your system is controlled by device special ﬁles,

which enable programs to be device independent. These ﬁles have been

shipped with permission settings that enable proper use and maximal

security.

If you install any other special ﬁles, refer to insf (1M) for the correct

permission settings.

Since device special ﬁles can be as vulnerable to tampering as any other

ﬁle, observe the following precautions:

• All device ﬁles should be kept in /dev.

• Protect the memory ﬁles, /dev/mem and /dev/kmem, from casual

access, since these ﬁles contain sensitive user information. For

example, a program that watches memory for an invocation of the

user types it in. The directory entries should look like:

crw-r----- 1 bin sys 3 0x000001 Jun 9 1996 /dev/kmem

crw-r----- 1 bin sys 3 0x000000 Jun 9 1996 /dev/mem