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IBM z/OS UNIX security parameters in /etc/rc must be properly specified.


Overview

Finding ID Version Rule ID IA Controls Severity
V-223618 ACF2-US-000030 SV-223618r533198_rule Medium
Description
Configuring the operating system to implement organization-wide security implementation guides and security checklists ensures compliance with federal standards and establishes a common security baseline across DoD that reflects the most restrictive security posture consistent with operational requirements.
STIG Date
IBM z/OS ACF2 Security Technical Implementation Guide 2022-06-22

Details

Check Text ( C-25291r504812_chk )
From the ISPF COMMAND SHELL enter:
ISHELL
/etc/rc

If all of the CHMOD commands in /etc/rc do not result in less restrictive access than what is specified in the tables below, this is not a finding.

NOTE: The use of CHMOD commands in /etc/rc is required in most environments to comply with the required settings, especially for dynamic objects such as the /dev directory.

The following represents a hierarchy for permission bits from least restrictive to most restrictive:

7 rwx (least restrictive)
6 rw-
3 -wx
2 -w-
5 r-x
4 r--
1 --x
0 --- (most restrictive)

If all of the CHAUDIT commands in /etc/rc do not result in less auditing than what is specified in the tables below this is not a finding.

NOTE: The use of CHAUDIT commands in /etc/rc may not be necessary. If none are found, there is not a finding.

The possible audit bits settings are as follows:
f log for failed access attempts
a log for failed and successful access
- no auditing

Directory Permission Bits User Audit Bits Function
/ [root] 755 faf Root level of all file systems. Holds critical mount points.
/bin 1755 fff Shell scripts and executables for basic functions
/dev 1755 fff Character-special files used when logging into the OMVS shell and during C language program compilation. Files are created during system IPL and on a per-demand basis.
/etc 1755 faf Configuration programs and files (usually with locally customized data) used by z/OS UNIX and other product initialization processes
/lib 1755 fff System libraries including dynamic link libraries and files for static linking
/samples 1755 fff Sample configuration and other files
/tmp 1777 fff Temporary data used by daemons, servers, and users. Note: /tmp must have the sticky bit on to restrict file renames and deletions.
/u 1755 fff Mount point for user home directories and optionally for third-party software and other local site files
/usr 1755 fff Shell scripts, executables, help (man) files and other data. Contains sub-directories (e.g., lpp) and mount points used by program products that may be in separate file systems.
/var 1775 fff Dynamic data used internally by products and by elements and features of z/OS UNIX.
Fix Text (F-25279r504813_fix)
Review the settings in the /etc/rc. The /etc/rcfile is the system initialization shell script. When z/OS UNIX kernel services start, /etc/rc is executed to set file permissions and ownership for dynamic system files and to perform other system startup functions such as starting daemons. There can be many commands in /etc/rc.

There are two specific guidelines that must be followed:
-Verify that the CHMOD or CHAUDIT command does not result in less restrictive security than what is specified in the table below.
-Immediately prior to each command that starts a daemon, the _BPX_JOBNAME variable must be set to match the daemon's name (e.g., inetd, syslogd). The use of _BPX_USERID is at the site’s discretion, but is recommended.

Directory Permission Bits User Audit Bits Function
/ [root] 755 faf Root level of all file systems. Holds critical mount points.
/bin 1755 fff Shell scripts and executables for basic functions
/dev 1755 fff Character-special files used when logging into the OMVS shell and during C language program compilation. Files are created during system IPL and on a per-demand basis.
/etc 1755 faf Configuration programs and files (usually with locally customized data) used by z/OS UNIX and other product initialization processes
/lib 1755 fff System libraries including dynamic link libraries and files for static linking
/samples 1755 fff Sample configuration and other files
/tmp 1777 fff Temporary data used by daemons, servers, and users. Note: /tmp must have the sticky bit on to restrict file renames and deletions.
/u 1755 fff Mount point for user home directories and optionally for third-party software and other local site files
/usr 1755 fff Shell scripts, executables, help (man) files and other data. Contains sub-directories (e.g., lpp) and mount points used by program products that may be in separate file systems.
/var 1775 fff Dynamic data used internally by products and by elements and features of z/OS UNIX.