The organization must identify authorized software programs and permit execution of authorized software. The process used to identify software programs that are authorized to execute on organizational information systems is commonly referred to as allow listing.
Using an allow list provides a configuration management method for allowing the execution of only authorized software. Using only authorized software decreases risk by limiting the number of potential vulnerabilities. Verification of allow listed software occurs prior to execution or at system startup.
User home directories/folders may contain information of a sensitive nature. Nonprivileged users should coordinate any sharing of information with an SA through shared resources.
RHEL 9 ships with many optional packages. One such package is a file access policy daemon called "fapolicyd". "fapolicyd" is a userspace daemon that determines access rights to files based on attributes of the process and file. It can be used to either block list or allow list processes or file access.
Proceed with caution with enforcing the use of this daemon. Improper configuration may render the system nonfunctional. The "fapolicyd" API is not namespace aware and can cause issues when launching or running containers.
If "fapolicyd" is not running in enforcement mode, this is a finding.
Check that "fapolicyd" employs a deny-all policy on system mounts with the following commands:
$ sudo tail /etc/fapolicyd/compiled.rules
allow exe=/usr/bin/python3.7 : ftype=text/x-python deny_audit perm=any pattern=ld_so : all deny perm=any all : all
If "fapolicyd" is not running with a deny-all, permit-by-exception policy, this is a finding.
Note: "deny_log" or "deny_audit" options meet the security requirements. These options will generate higher volumes of logs.
Fix
Configure RHEL 9 to employ a deny-all, permit-by-exception application allow listing policy with "fapolicyd".
With the "fapolicyd" installed and enabled, configure the daemon to function in permissive mode until the allow list is built correctly to avoid system lockout. Do this by editing the "/etc/fapolicyd/fapolicyd.conf" file with the following line:
permissive = 1
Build the allow list in a file within the "/etc/fapolicyd/rules.d" directory, ensuring the last rule implements a deny-all policy, such as "deny perm=any all : all".
Once it is determined the allow list is built correctly, set the "fapolicyd" to enforcing mode by editing the "permissive" line in the /etc/fapolicyd/fapolicyd.conf file.