Controlling Access to a Computer System

In the workplace, all computers that are connected to a server can be thought of as one large multifaceted system. You are responsible for the security of this larger system. You need to defend the network from outsiders who are trying to gain access. You also need to ensure the integrity of the data on the computers within the network.

At the file level, Oracle Solaris provides standard security features that you can use to protect files, directories, and devices. At the system and network levels, the security issues are mostly the same. The first line of security defense is to control access to your system, as described in the following sections.

Maintaining Physical Security

To control access to your system, you must maintain the physical security of your computing environment. For instance, a system that is logged in and left unattended is vulnerable to unauthorized access. An intruder can gain access to the operating system and to the network. The computer's surroundings and the computer hardware must be physically protected from unauthorized access.

You can protect a SPARC system from unauthorized access to the hardware settings. Use the eeprom command to require a password to access the PROM. For more information, see How to Require a Password for SPARC Hardware Access. To protect x86 hardware, consult the vendor documentation.

Maintaining Login Control

You also must prevent unauthorized logins to a system or the network, which you can do through password assignment and login control. All accounts on a system must have a password. A password is a simple authentication mechanism. An account without a password makes your entire network accessible to an intruder who guesses a user name. A strong password algorithm protects against brute force attacks.

When a user logs in to a system, the login command checks the appropriate naming service or directory service database according to the information in the name switch service, svc:/system/name-service/switch. The following databases can affect login:

• files – Designates the /etc files on the local system

• ldap – Designates the LDAP directory service on the LDAP server

• nis – Designates the NIS database on the NIS master server

• dns – Designates the domain name service on the network

For a description of the naming service, see the nscd(1M) man page. For information about naming services and directory services, see Oracle Solaris Administration: Naming and Directory Services.

The login command verifies the user name and password that were supplied by the user. If the user name is not in the password database, the login command denies access to the system. If the password is not correct for the user name that was specified, the login command denies access to the system. When the user supplies a valid user name and its corresponding password, the system grants the user access to the system.

PAM modules can streamline login to applications after a successful system login. For more information, see Chapter 14, Using Pluggable Authentication Modules.

Sophisticated authentication and authorization mechanisms are available on Oracle Solaris systems. For a discussion of authentication and authorization mechanisms at the network level, see Authentication and Authorization for Remote Access.

Managing Password Information

When users log in to a system, they must supply both a user name and a password. Although logins are publicly known, passwords must be kept secret. Passwords should be known only to each user. Users must choose their passwords carefully and change them often.

Passwords are initially created when you set up a user account. To maintain security on user accounts, you can set up password aging to force users to routinely change their passwords. You can also disable a user account by locking the password. For detailed information about administering passwords, see Chapter 1, Managing User Accounts and User Environments (Overview), in Managing User Accounts and User Environments in Oracle Solaris 11.1 and the passwd(1) man page.

Local Passwords

If your network uses local files to authenticate users, the password information is kept in the system's /etc/passwd and /etc/shadow files. The user name and other information are kept in the /etc/passwd file. The encrypted password itself is kept in a separate shadow file, /etc/shadow. This security measure prevents a user from gaining access to the encrypted passwords. While the /etc/passwd file is available to anyone who can log in to a system, only the root account can read the /etc/shadow file. You can use the passwd command to change a user's password on a local system.

NIS Passwords

If your network uses NIS to authenticate users, password information is kept in the NIS password map. NIS does not support password aging. You can use the command passwd -r nis to change a user's password that is stored in an NIS password map.

LDAP Passwords

The Oracle Solaris LDAP naming service stores password information and shadow information in the ou=people container of the LDAP directory tree. On the Oracle Solaris LDAP naming service client, you can use the passwd -r ldap command to change a user's password. The LDAP naming service stores the password in the LDAP repository.

Password policy is enforced on the Oracle Directory Server Enterprise Edition. Specifically, the client's pam_ldap module follows the password policy controls that are enforced on the Oracle Directory Server Enterprise Edition. For more information, see LDAP Naming Services Security Model in Working With Naming and Directory Services in Oracle Solaris 11.1.

Password Encryption

Strong password encryption provides an early barrier against attack. Oracle Solaris software provides six password encryption algorithms. The Blowfish, MD5, and SHA algorithms provide robust password encryption.

Password Algorithm Identifiers

You specify the algorithms configuration for your site in the /etc/security/policy.conf file. In the policy.conf file, the algorithms are named by their identifier, as shown in the following table. For the identifier-algorithm mapping, see the /etc/security/crypt.conf file.

Table 2-1 Password Encryption Algorithms

Algorithms Configuration in the policy.conf File

The following shows the default algorithms configuration in the policy.conf file:

#
…
# crypt(3c) Algorithms Configuration
#
# CRYPT_ALGORITHMS_ALLOW specifies the algorithms that are allowed
to
# be used for new passwords.  This is enforced only in crypt_gensalt(3c).
#
CRYPT_ALGORITHMS_ALLOW=1,2a,md5,5,6

# To deprecate use of the traditional unix algorithm, uncomment below
# and change CRYPT_DEFAULT= to another algorithm.  For example,
# CRYPT_DEFAULT=1 for BSD/Linux MD5.
#
#CRYPT_ALGORITHMS_DEPRECATE=__unix__

# The Oracle Solaris default is a SHA256 based algorithm.  To revert to
# the policy present in Solaris releases set CRYPT_DEFAULT=__unix__,
# which is not listed in crypt.conf(4) since it is internal to libc.
#
CRYPT_DEFAULT=5
…

When you change the value for CRYPT_DEFAULT, the passwords of new users are encrypted with the algorithm that is associated with the new value.

When existing users change their passwords, how their old password was encrypted affects which algorithm is used to encrypt the new password. For example, assume that CRYPT_ALGORITHMS_ALLOW=1,2a,md5,5,6, and CRYPT_DEFAULT=1. The following table shows which algorithm would be used to generate the encrypted password.

For more information about configuring the algorithm choices, see the policy.conf(4) man page. To specify password encryption algorithms, see Changing the Default Algorithm for Password Encryption (Tasks).

Special System Accounts

The root account is one of several special system accounts. Of these accounts, only the root account is assigned a password and can log in. The nuucp account can log in for file transfers. The other system accounts either protect files or run administrative processes without using the full powers of root.

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Caution - Never change the password setting of a system account. System accounts from Oracle Solaris are delivered in a safe and secure state.

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The following table lists some system accounts and their uses. The system accounts perform special functions. Each account has a UID that is less than 100.

Table 2-2 Selected System Accounts and Their Uses

Remote Logins

Remote logins offer a tempting avenue for intruders. Oracle Solaris provides several commands to monitor, limit, and disable remote logins. For procedures, see Securing Logins and Passwords (Task Map).

By default, remote logins cannot gain control or read certain system devices, such as the system mouse, keyboard, frame buffer, or audio device. For more information, see the logindevperm(4) man page.