Maintaining Login Control

You can prevent unauthorized logins to a system or the network through password assignment and login control. A password is a simple authentication mechanism. All accounts on a system must have a password. 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. To change values in a naming service database, you use the SMF commands. The naming services indicate the location of the databases that 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 Working With Oracle Solaris 11.2 Directory and Naming Services: DNS and NIS and Working With Oracle Solaris 11.2 Directory and Naming Services: LDAP .

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 logging in to applications after a successful system login. For more information, see Chapter 1, Using Pluggable Authentication Modules, in Managing Kerberos and Other Authentication Services in Oracle Solaris 11.2 .

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, About User Accounts and User Environments, in Managing User Accounts and User Environments in Oracle Solaris 11.2 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 names and other information are kept in the /etc/passwd file. The encrypted passwords themselves are 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 Oracle Directory Server Enterprise Edition. For more information, see LDAP Naming Services Security Model in Working With Oracle Solaris 11.2 Directory and Naming Services: LDAP .

Password Encryption

Strong password encryption provides an early barrier against attack. Oracle Solaris software provides six password encryption algorithms. The Blowfish 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 1-1  Password Encryption Algorithms

Identifier Description Algorithm Man Page 1 The MD5 algorithm that is compatible with MD5 algorithms on BSD and Linux systems. crypt_bsdmd5(5) 2a The Blowfish algorithm that is compatible with the Blowfish algorithm on BSD systems. Note -  To promote FIPS 140 security, remove the Blowfish algorithm (2a) from the CRYPT_ALGORITHMS_ALLOW=2a,5,6 entry in the /etc/security/policy.conf file. crypt_bsdbf(5) md5 The Sun MD5 algorithm, which is considered stronger than the BSD and Linux version of MD5. crypt_sunmd5(5) 5 The SHA256 algorithm. SHA stands for Secure Hash Algorithm. This algorithm is a member of the SHA-2 family. SHA256 supports 255-character passwords. This algorithm is the default, (CRYPT_DEFAULT). crypt_sha256(5) 6 The SHA512 algorithm. crypt_sha512(5) __unix__ Deprecated. The traditional UNIX encryption algorithm. This algorithm can be of use when connecting to old systems. crypt_unix(5)

Algorithms Configuration in the policy.conf File

The default algorithms configuration in the policy.conf file is as follows:

#
…
# 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, the way 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=6. The following table shows which algorithm would be used to generate the encrypted password. The password consists of identifier=algorithm.

Initial Password Changed Password Explanation 1 = crypt_bsdmd5 Uses same algorithm The 1 identifier is in the CRYPT_ALGORITHMS_ALLOW list. The user's password continues to be encrypted with the crypt_bsdmd5 algorithm. 2a = crypt_bsdbf Uses same algorithm The 2a identifier is in the CRYPT_ALGORITHMS_ALLOW list. Therefore, the new password is encrypted with the crypt_bsbdf algorithm. md5 = crypt_md5 Uses same algorithm The md5 identifier is in the CRYPT_ALGORITHMS_ALLOW list. Therefore, the new password is encrypted with the crypt_md5 algorithm. 5 = crypt_sha256 Uses same algorithm The 5 identifier is in the CRYPT_ALGORITHMS_ALLOW list. Therefore, the new password continues to be encrypted with the crypt_sha256 algorithm. 6 = crypt_sha512 Uses same algorithm The 6 identifier is s the value of CRYPT_DEFAULT. Therefore, the new password continues to be encrypted with the crypt_sha512 algorithm. __unix__ = crypt_unix Uses crypt_sha512 algorithm The __unix__ identifier is not in the CRYPT_ALGORITHMS_ALLOW list. Therefore, the crypt_unix algorithm cannot be used. The new password is encrypted with the CRYPT_DEFAULT algorithm.

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.

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.

The following table lists some system accounts and their uses. The system accounts perform special functions. Each account on this list has a UID that is less than 100. For a full listing of system files, use the command logins –s.

Table 1-2  Selected System Accounts and Their Uses

System Account UID Use root 0 Has almost no restrictions. Can override other protections and permissions. The root account has access to the entire system. The password for the root account should be very carefully protected. The root account owns most of the Oracle Solaris commands. daemon 1 Controls background processing. bin 2 Owns some Oracle Solaris commands. sys 3 Owns many system files. adm 4 Owns some administrative files. lp 71 Owns the object data files and spooled data files for the printer. uucp 5 Owns the object data files and spooled data files for UUCP, the UNIX-to-UNIX copy program. nuucp 9 Used by remote systems to log in to the system and start file transfers.

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 Table 3–1.

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.