IBM z/OS VTAM USSTAB definitions must not be used for unsecured terminals.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-224105	TSS0-VT-000020	SV-224105r877945_rule		Medium

Description
If the operating system were to allow any user to make changes to software libraries, then those changes might be implemented without undergoing the appropriate testing and approvals that are part of a robust change management process. This requirement applies to operating systems with software libraries that are accessible and configurable, as in the case of interpreted languages. Software libraries also include privileged programs which execute with escalated privileges. Only qualified and authorized individuals will be allowed to obtain access to information system components for purposes of initiating changes, including upgrades and modifications.

Description

If the operating system were to allow any user to make changes to software libraries, then those changes might be implemented without undergoing the appropriate testing and approvals that are part of a robust change management process. This requirement applies to operating systems with software libraries that are accessible and configurable, as in the case of interpreted languages. Software libraries also include privileged programs which execute with escalated privileges. Only qualified and authorized individuals will be allowed to obtain access to information system components for purposes of initiating changes, including upgrades and modifications.

STIG	Date
IBM z/OS TSS Security Technical Implementation Guide	2024-02-22

Details

Check Text ( C-25778r516714_chk )
Ask the system administrator to supply the following information: - Documentation regarding terminal naming standards. - Documentation of all procedures controlling terminal logons to the system. - A complete list of all USS commands used by terminal users to log on to the system. - Members and data set names containing USSTAB and LOGAPPL definitions of all terminals that can log on to the system (e.g., SYS1.VTAMLST). - Members and data set names containing logon mode parameters. If USSTAB definitions are only used for secure terminals (e.g., terminals that are locally attached to the host or connected to the host via secure leased lines), this is not a finding. If USSTAB definitions are used for any unsecured terminals (e.g., dial up terminals or terminals attached to the Internet such as TN3270 or KNET 3270 emulation), this is a finding.

Check Text ( C-25778r516714_chk )

Ask the system administrator to supply the following information:

- Documentation regarding terminal naming standards.
- Documentation of all procedures controlling terminal logons to the system.
- A complete list of all USS commands used by terminal users to log on to the system.
- Members and data set names containing USSTAB and LOGAPPL definitions of all terminals that can log on to the system (e.g., SYS1.VTAMLST).
- Members and data set names containing logon mode parameters.

If USSTAB definitions are only used for secure terminals (e.g., terminals that are locally attached to the host or connected to the host via secure leased lines), this is not a finding.

If USSTAB definitions are used for any unsecured terminals (e.g., dial up terminals or terminals attached to the Internet such as TN3270 or KNET 3270 emulation), this is a finding.

Fix Text (F-25766r516715_fix)
Configure USSTAB definitions to be only used for secure terminals. Only terminals that are locally attached to the host or connected to the host via secure leased lines located in a secured area. Only authorized personnel may enter the area where secure terminals are located. USSTAB or LOGAPPL definitions are used to control logon from secure terminals. These terminals can log on directly to any VTAM application (e.g., TSO, CICS, etc.) of their choice and bypass Session Manager services. Secure terminals are usually locally attached to the host or connected to the host via a private LAN without access to an external network. Only authorized personnel may enter the area where secure terminals are located.

Fix Text (F-25766r516715_fix)

Configure USSTAB definitions to be only used for secure terminals.

Only terminals that are locally attached to the host or connected to the host via secure leased lines located in a secured area. Only authorized personnel may enter the area where secure terminals are located.

USSTAB or LOGAPPL definitions are used to control logon from secure terminals. These terminals can log on directly to any VTAM application (e.g., TSO, CICS, etc.) of their choice and bypass Session Manager services. Secure terminals are usually locally attached to the host or connected to the host via a private LAN without access to an external network. Only authorized personnel may enter the area where secure terminals are located.