Title

IBM z/OS UNIX HFS permission bits and audit bits for each directory must be properly protected. (Cat II impact)

Discussion

To mitigate the risk of unauthorized access to sensitive information by entities that have been issued certificates by DoD-approved PKIs, all DoD systems (e.g., web servers and web portals) must be properly configured to incorporate access control methods that do not rely solely on the possession of a certificate for access. Successful authentication must not automatically give an entity access to an asset or security boundary. Authorization procedures and controls must be implemented to ensure each authenticated entity also has a validated and current authorization. Authorization is the process of determining whether an entity, once authenticated, is permitted to access a specific asset. Information systems use access control policies and enforcement mechanisms to implement this requirement. Access control policies include: identity-based policies, role-based policies, and attribute-based policies. Access enforcement mechanisms include: access control lists, access control matrices, and cryptography. These policies and mechanisms must be employed by the application to control access between users (or processes acting on behalf of users) and objects (e.g., devices, files, records, processes, programs, and domains) in the information system. Satisfies: SRG-OS-000080-GPOS-00048, SRG-OS-000259-GPOS-00100

Check Content

From the ISPF Command Shell enter: omvs enter CD / enter ls -alW If the HFS permission bits and user audit bits for each directory and file match or are more restrictive than the specified settings listed in the SYSTEM DIRECTORY SECURITY SETTINGS table below, this is not a finding. 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) The possible audit bits settings are as follows: f log for failed access attempts a log for failed and successful access - no auditing SYSTEM DIRECTORY SECURITY SETTINGS 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

Configure the UNIX permission bits and user audit bits on each of the HFS directories in the table SYSTEM DIRECTORY SECURITY SETTINGS below to be equal or more restrictive. 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) The possible audit bits settings are as follows: f log for failed access attempts a log for failed and successful access - no auditing SYSTEM DIRECTORY SECURITY SETTINGS 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. The following commands are a sample of the commands to be used (from a user account with an effective UID(0)) to update the permission bits and audit bits: chmod 0755 / chaudit w=sf,rx+f / chmod 0755 /bin chaudit rwx=f /bin

Additional Identifiers

Rule ID: SV-224082r958472_rule

Vulnerability ID: V-224082

Group Title: SRG-OS-000080-GPOS-00048

Expert Comments

CCIs tied to check.

Controls tied to check. These are derived from the CCIs shown above.