OpenVMS Guide to System Security

This specification permits the user to run batch jobs only during the hours of 6:00 p.m. through 8:59 a.m. on primary days but all day on secondary days.

7.1.2 Restricting Modes of Operation

The following concerns might cause you to prohibit network access for some of your users:

• The user has data that should be accessed only through the local node.
• Penetration attempts are more likely to occur over a network because of the increased anonymity of the connection. (This concern is also relevant to dialup connections.)

Use the AUTHORIZE qualifier /NONETWORK to prevent specific users from having network access, as shown in the following example:

UAF> ADD JSMITH /NONETWORK, ...

Any of the AUTHORIZE access mode qualifiers (/LOCAL, /REMOTE, /DIALUP, /INTERACTIVE, /BATCH, or /NETWORK) can be negated in this manner to restrict access to the system.

7.1.3 Restricting Account Duration

It is good practice to set an account expiration time that matches the maximum length of time you expect the user to require access. When the expiration time arrives, the system automatically prohibits access to the account. You must still remove the UAF record and delete the user's files.

Use of the /EXPIRATION qualifier also forces you to periodically review accounts and reauthorize only those that are necessary.

To set the account expiration time, use the AUTHORIZE qualifier /EXPIRATION in the user's UAF record. For example, the following qualifier specifies that the user's account will expire on the 30th of December 1995:

/EXPIRATION=30-DEC-1995 

You may want to severely restrict the use of certain accounts. For example, you may want to disable specific accounts used only periodically, such as the SYSTEST and FIELD accounts, to limit possible misuse of these accounts. Disable the accounts with the /FLAGS=DISUSER qualifier. Temporarily enable the accounts with the /FLAGS=NODISUSER qualifier when needed.

7.1.5 Restricting Disk Volumes

Identify the user's default device and directory in the UAF record with the AUTHORIZE qualifiers /DEVICE and /DIRECTORY. You can limit the number of blocks available to the user on that disk (and any other disk) through the disk quota feature of the System Management utility (SYSMAN), as described in the OpenVMS System Management Utilities Reference Manual: A--L.

The volume protection in place on other disks controls how much access a user can obtain to the disks. The user's privileges, which can be extended or limited through the AUTHORIZE qualifier /PRIVILEGES, also influence the access available (see Section 8.7).

7.1.6 Marking Accounts for External Authentication

Mark a user's account in the UAF record with the AUTHORIZE qualifier /FLAGS=EXTAUTH to allow the user to be externally authenticated.

See Section 7.4 for more information.

7.2 Assigning Appropriate Accounts to Users

The type of system access a user holds largely depends on his or her need for system resources and your site's security requirements. This section describes the types of user accounts that are available on OpenVMS systems and explains why one type of account may be preferable to another. For a step-by-step description of adding user accounts, refer to the OpenVMS System Manager's Manual.

7.2.1 Types of System Accounts

There are two major types of accounts:

• Interactive accounts have access to system software. Usually, such an account is considered an individual account.
• Limited-access accounts provide controlled login to the system and, in some cases, controlled access to user software. Limited-access accounts ensure that the system and process login command procedures, as well as any command procedures they call, are executed. There are two types of limited accounts: captive and restricted. Guest, proxy, and automatic login accounts are forms of captive and restricted accounts. DECwindows software does not currently support captive or restricted logins in the traditional sense. Once a user is logged in and creates a DECterm window, however, the traditional environment of a captive or restricted account applies.

Both interactive and limited-access accounts can be privileged accounts, and can be externally authenticated, as Section 7.2.2 describes.

The following table shows the kind of account to create based on the task a user performs:

If User Needs to...	Type of Account to Create
Perform work of a general nature, such as program development or text editing	Interactive
Perform routine computer tasks requiring limited activities	Captive
Run batch operations during unsupervised periods	Captive
Run applications programs with confidential information	Captive
Use network applications like MAIL	Restricted
Access resources on your system from a remote system (in a limited manner)	Captive or restricted
Use network proxy accounts	Restricted
Use authentication systems like smart cards	Restricted
Use accounts created as part of a layered product installation (such as the NOTES$SERVER account created during the installation of DEC Notes)	Restricted
Perform privileged operations	Interactive, restricted, or captive
Access resources from a remote system without a password	Captive
Automatically log in to an application terminal	Captive or restricted
Log in at the OpenVMS login prompt using their external user IDs and passwords	Externally authenticated

You may develop one or more templates that work for many of your users. However, do not oversimplify the process of account creation to the point that you simply apply a template. The danger in relying solely on templates is that you might overlook special considerations that apply to individual users, thereby forfeiting important controls that only you can exercise.

Examine templates regularly to be sure they are valid and reflect the way you want your operations to proceed. Templates become obsolete rapidly.

7.2.1.1 Interactive Account Example

Example 7-1 shows creating an interactive user account with moderate restrictions, typical of an account at a commercial site where security is a concern and the average user has limited access. Notice the following:

1. Only one password is required.
2. The password has a minimum length of 6 characters.
3. The user's password is valid for 90 days, a much longer lifetime than the manager's password shown in Example 6-1.
4. The user is allowed access during the week and on Saturdays.
5. During those six days, the user has access during a 15-hour period.

Example 7-1 Creating a Typical Interactive User Account

$ SET DEFAULT SYS$SYSTEM
$ RUN AUTHORIZE
UAF> ADD RDOGWOOD /PASSWORD=TRALAYAM/UIC=[231,010] -  (1)
_UAF> /DEVICE=BOTANYDEV/DIRECTORY=[RDOGWOOD] -
_UAF> /OWNER="Robert Dogwood"/ACCOUNT=BOTNYDPT -
_UAF> /FLAGS=(GENPWD)/PWDMINIMUM=6 -                  (2)
_UAF> /EXPIRATION=15-JUNE-1994/PWDLIFETIME=90-        (3)
_UAF> /PRIMEDAYS=(MON,TUES,WED,THURS,FRI,SAT,NOSUN) - (4)
 
_UAF> /NOACCESS=(PRIMARY,23-6,SECONDARY)/NODIALUP     (5)
identifier for value:[000231,000010] added to RIGHTSLIST.DAT
UAF>

Example 7-2 shows creating an applications production account where the user is highly restricted. This account is designed to perform two functions: list the grades at State University, and produce mailings to each student's home.

In the example, any value not specified defaults to the value provided by the default record in SYSUAF.DAT.

Notice the following:

1. Account users do not see the normal system welcome message. The account may not receive mail. It is restricted to running under control of its login command procedure and the default command interpreter (DCL).
2. The user who initiates the login must specify the password, GROBWACH. (Most likely only the security administrator will change the password.)
3. When the job is run through a local login, it is restricted to the hours of 8 a.m. through 5:59 p.m., Monday through Friday. (Notice that only batch and local logins are allowed, and batch mode does not have time restrictions.)
4. The job may not be run over dialup lines or as a remote job. The account also denies network access.
5. The process runs under the control of a special login command procedure (GRADES.COM), which presumably provides the operator with a menu of functions.
6. The process is restricted to the commands defined in the CLI table GRADES_TABLES.

Example 7-2 Creating a Limited-Access Account

$ SET DEFAULT SYS$SYSTEM
$ RUN AUTHORIZE
UAF> ADD REPGRADES /DEVICE=ADMINDEV/DIRECTORY=[REPGRADES] -
 
_UAF> /FLAGS=(CAPTIVE,DISWELCOME,DISNEWMAIL,DISMAIL,DEFCLI) - (1)
_UAF> /PASSWORD=GROBWACH/UIC=[777,031] -      (2)
_UAF> /OWNER="Campus Admin"/ACCOUNT=ADMIN -
 
_UAF> /LOCAL=(PRIMARY,8-17)/PRIMEDAYS=(MON,TUES,WED,THU, - (3)
_UAF> FRI,NOSAT,NOSUN) - 
 
_UAF> /NONETWORK/NOREMOTE/NODIALUP -          (4)
_UAF> /LGICMD=GRADES (5) /CLITABLES=GRADES_TABLES -   (6)
 
   .
   .
   .
user record successfully added
identifier for value:[000777,000031] added to RIGHTSLIST.DAT

Privileges determine what functions users are authorized to perform on the system. Any account with privileges beyond TMPMBX and NETMBX is considered privileged. Such an account can be interactive, restricted, or captive.

Because abuse of privileged accounts can result in serious losses, consider imposing special controls on accounts with the most powerful privileges as follows:

• Limit access to the account. For example, you can prohibit dialup or network access with the /NODIALUP or /NONETWORK qualifier to discourage outsiders from attempting break-ins from remote locations.
• Impose security alarms to detect use of the privileges pertaining to file protection: BYPASS, SYSPRV, READALL, and GRPPRV. For information about setting up and monitoring security alarms, see Chapter 9.

For all but the SYSTEM account, also add the following restrictions:

• Use the /PRIMEDAYS and /NOACCESS qualifiers to restrict the time of day or days of the week that logins can be performed. Select periods of time that can be monitored for appropriate use.
• Disable the account when not in use with the AUTHORIZE qualifier /FLAGS=DISUSER.
• Use a captive login command procedure for additional validation. Captive login command procedures are described in Section 7.2.4.

Naturally, you need to set controls on the SYSTEM account. The most secure practice is to disable it for all but batch access and perform system management through individual privileged user accounts, which provide accountability.

Special-Purpose Privileged Captive Accounts

Because the safety of a captive account depends on the integrity of its command procedures, it is unadvisable to set up privileged captive accounts for untrusted users. However, there are some situations that require privilege, and it is safer to perform specific sensitive functions through captive privileged accounts than through general purpose privileged accounts. For example, users who perform backup operations require the READALL privilege. By making the account that performs backups captive, you can ensure that the procedures are carried out according to your system's backup policy.

See Section 7.2.4 for guidelines for setting up captive accounts.

7.2.3 Interactive Accounts

Interactive accounts are very common in environments with low to moderate security requirements. They are well suited to work of a general nature, such as program development or text editing. The OpenVMS System Manager's Manual explains the procedure for setting up this type of account. Section 7.2.1.1 provides an example.

7.2.4 Captive Accounts

A captive account limits the activities of the user and, when properly administered, denies the user access to the DCL command level. You can set up the account to limit the user to running under the complete control of a specific program or the captive login command procedure.

The primary feature of the captive account is its login command procedure. This type of account ensures that the system login command procedure (SYLOGIN.COM) and the process login command procedure (specified by the /LGICMD qualifier in SYSUAF.DAT), as well as any command procedures they call, are executed. A user cannot specify any of the qualifiers shown in Table 7-2 to modify the captive command procedures when logging in.

Once logged in to a captive account, a user cannot escape to the DCL command level through the Ctrl/Y sequence, the SPAWN command, or the INQUIRE command. Because the DISCTLY flag in the UAF record is turned on, any use of Ctrl/Y fails. If unhandled errors or attempted interrupts occur, a system error message is generated, and the session is logged out. Unless the SPAWN command carries the /TRUSTED qualifier, it is ineffective within a captive account. SPAWN is also disabled from MAIL and the DEC Text Processing Utility (DECTPU) (as a built-in procedure). The INQUIRE command is also disabled to prevent the possible execution of user-specified lexical functions.

Table 7-2 Login Qualifiers Not Allowed by Captive Accounts

Qualifier	Description
/CLI	Specifies the name of an alternate command language interpreter
/COMMAND	Overrides the default login command procedure
/NOCOMMAND	Disables execution of the default login command procedure
/DISK	Requests an alternate default disk
/TABLES	Specifies the name of an alternate CLI table

7.2.4.1 Setting Up Captive Accounts

You define a captive account with AUTHORIZE by including the following qualifier when creating the account:

/FLAGS=(CAPTIVE) 

A captive account also requires the qualifiers described in Table 7-3.

Table 7-3 Qualifiers Required to Define Captive Accounts

Qualifier	Action
/LGICMD	Identifies the captive account login command procedure and overrides the default login command procedure (LOGIN.COM in the user's default directory).
/UIC	Assigns a unique UIC group. Use the following form of the AUTHORIZE command SHOW to verify the uniqueness of the UIC group: SHOW [groupuic,*] By keeping the account in a separate group, you can ensure that the captive account users can access only world-accessible files and files owned by the captive account. It ensures that the account is not a member of the system group (that is, has a group value less than or equal to 10 2, unless modified by the system parameter MAXSYSGROUP).
/NOPASSWORD or /FLAGS=LOCKPWD	Sets up the password. With a captive account, either require no password, or lock the password so that only the security administrator can change it. Locked passwords are generally preferable to open captive accounts (those with no password). If you assign a locked password, give that password to all users of the captive account.
/PRCLM	Sets the subprocess limit to 0, thus preventing the user from spawning out of the account. (Verify that the system parameter PQL_MPRCLM---the minimum subprocess limit---is set to 0.)

In addition to the required settings, you may want to specify additional characteristics for the account:

• You may want to disable the welcome announcement and electronic mail for the captive account. This is done by setting the DISWELCOME, DISMAIL, and DISNEWMAIL login flags.
• You may want to allow only interactive use of the account from a local terminal. Include the qualifiers /NODIALUP, /NOREMOTE, /NOBATCH, and /NONETWORK when establishing the account.
• Your application may have special requirements. You may need to impose additional AUTHORIZE qualifiers on the account, such as /NODIALUP, to restrict modes of operation. Consider imposing restrictions for the periods of the day and days of the week when the process can run.
• You can define a special set of DCL tables by using the /CLITABLES qualifier, or you can emulate DCL through the use of a DCL command procedure. It is more efficient to define DCL tables than to resort to a DCL command procedure to emulate DCL. See the description of the Command Definition utility (CDU) in the OpenVMS System Management Utilities Reference Manual: A--L for help when defining the DCL tables. Be aware that the DCL tables defined by the /CLITABLES qualifier are not used in network jobs, such as those using the TASK object.
• You can grant privileges, although you rarely need to grant any privilege other than TMPMBX to a captive account.
• You can limit the disk quota for the captive account to the amount needed.

When writing captive command procedures for your site, be sure to observe the following guidelines:

• Use the DCL command READ/PROMPT in command procedures. For example, to request the user to enter the date, enter the following command in the command procedure:

  READ/PROMPT="Enter date: " SYS$COMMAND DATE 
  

• Avoid use of the INQUIRE command in a captive command procedure. It produces an error that, if unhandled by a previous ON declaration, results in deletion of the process.
• When user input is required, never execute it directly. First compare it to what is expected, and screen for illegal characters such as apostrophe ('), at sign (@), dollar sign ($), quotation mark ("), ampersand (&), and hyphen (-).
• Avoid any use of the construction 'x, where x contains a string entered by the user. Never permit a restricted command procedure to attempt an evaluation of a symbol that the user enters. Use of lexical functions could break the command procedure.
• Avoid executing a line in a captive command procedure that contains the characters @TT:.
• Put Audit ACEs on the captive command procedure and its home directory to detect any modification of the file. See Section 9.2.1.2 for more information on Audit ACEs.
• If the captive account user is allowed to create or perform other operations on files, make certain that write access to the login command procedure and its directory is denied. (The user does need execute access.)
  If the function of the command procedure requires text preparation, you may need to give users access to a text editor. Use caution, however. Editors such as TECO or DECTPU can be dangerous because users can manipulate files and exit from the editor to the DCL interface. When designing this environment, remember that most text editors are capable of reading and writing files (within the access rights of the account). Provide an editor that gives users the tools they require but does not allow them to escape from the captive environment.

Example 7-3 and Example 7-4 provide sample command procedures for privileged and unprivileged accounts.

Example 7-3 Sample Captive Procedure for Privileged Accounts

 
$ if f$mode() .nes. "INTERACTIVE" then $logout 
$ term = f$logical("SYS$COMMAND") 
$ if f$locate("_T", term) .eq. 0 then $goto allow 
$ if f$locate("_OP",term) .ne. 0 then $logout 
$allow: 
$ set control=(y,t) 

Example 7-4 Sample Captive Command Procedure for Unprivileged Accounts

$ deassign sys$input 
$ previous_sysinput == f$logical("SYS$INPUT") 
$ on error then goto next_command 
$ on control_y then goto next_command 
$ set control=(y,t) 
$ 
$next_command: 
$ on error then goto next_command 
$ on control_y then goto next_command 
$ 
$ if previous_sysinput .nes. f$logical("SYS$INPUT") then deassign sys$input 
$ read/end=next_command/prompt="$ " sys$command command 
$ command == f$edit(command,"UPCASE,TRIM,COMPRESS") 
$ if f$length(command) .eq. 0 then goto next_command 
$ 
$ delete = "delete" 
$ delete/symbol/local/all 
$ if f$locate("@",command) .ne. f$length(command) then goto illegal_command 
$ if f$locate("=",command) .ne. f$length(command) then goto illegal_command 
$ if f$locate("F$",command) .ne. f$length(command) then goto illegal_command 
$ verb = f$element(0," ",command) 
$ 
$ if verb .eqs. "LOGOUT" then goto do_logout 
$ if verb .eqs. "HELP" then goto do_help 
$ 
$ write sys$output "%CAPTIVE-W-IVVERB, unrecognized command \",verb,"\" 
$ goto next_command 
$ 
$illegal_command: 
$ write sys$output "%CAPTIVE-W-ILLEGAL, bad characters in command line" 
$ goto next_command 
$ 
$do_logout: 
$ logout 
$ goto next_command 
$ 
$do_help: 
$ define sys$input sys$command 
$ help 
$ goto next_command 

Certain limited-access accounts require a less restrictive environment than captive accounts. Accounts under which network objects run, for example, require temporary access to DCL. Such accounts must be set up as restricted accounts, not captive accounts. Restricted accounts are indistinguishable from regular accounts once the login sequence finishes. The purpose behind restricted accounts is to ensure a trusted login wherein SYLOGIN, LOGIN, and their descendants execute completely.

Define a restricted account with the Authorize utility by including the following qualifier when creating the account:

/FLAGS=(RESTRICTED) 

This flag ensures that the account is noted as restricted. A restricted account provides the same features as those listed for a captive account in Section 7.2.4 except that restricted accounts allow the user access to the DCL command level following the execution of the system and process login command procedures.

Sometimes it is appropriate to allow the user to enter the Ctrl/Y key sequence after the command procedure starts. For example:

• You may want to provide users with a Ctrl/Y feature at points during the execution of the restricted login command procedure. Include ON CONTROL_Y commands in the procedure where you want to test for the Ctrl/Y features, as shown in Example 7-4.
• You may have a restricted command procedure that ultimately turns control over to the user. For example, consider a SYLOGIN.COM command procedure that performs additional security validation; its execution should be guaranteed to ensure its effectiveness. However, once SYLOGIN.COM has done its job, control can be passed to the user. To do this, mark the account as restricted, and enter the DCL command SET CONTROL=Y when you are ready to release control to the user.

To force individuals at specific terminals to log in to an application program, create a separate captive account for the application. Then set up automatic logins to the new account for the desired users using the System Management utility (SYSMAN).

Once you set up a terminal for automatic login, it can be used only for the designated account. This is most useful for applications terminals used by people who may be unfamiliar with computers.

The automatic login feature suppresses the user name prompt. All other login features (system password, primary and secondary passwords, and messages) function normally, if enabled.

Passwords are optional. If you want the account to be open to all users where the terminals are located, eliminate the password. When no password is required, the user has no data to enter at login. The operating system logs the terminal in automatically in response to the Break key or the Return key and immediately enters the application if the account is under the control of a captive login command procedure.

The automatic login file (ALF) lists the terminals and the users who are authorized to access the application account. However, automatic login accounts are potentially accessible from terminals and sources other than the terminals listed in the ALF file and, therefore, require protection, especially if they have no password. Use the following precautions:

• Restrict network and dialup access, as appropriate, with the AUTHORIZE qualifiers /NODIALUP, /NONETWORK, and /NOREMOTE.
• Set the AUTOLOGIN flag in the account's UAF record. This flag makes the account available only by autologin, batch, and network proxy.

Guest accounts are forms of captive or restricted accounts that allow multiple remote users access to resources on your system through a common account. For example, users across the network may need access to your system to report problems or to read corporate memos.

  6346P010.HTM
  OSSG Documentation
  22-NOV-1996 13:05:04.96

Copyright © Digital Equipment Corporation 1996. All Rights Reserved.

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