Vulnerability Discussion

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 whitelisting.

Utilizing a whitelist 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 whitelisted software occurs prior to execution or at system startup.

User home directories/folders may contain information of a sensitive nature. Non-privileged users should coordinate any sharing of information with an SA through shared resources.

RHEL 8 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 blacklist or whitelist processes or file access.

Proceed with caution with enforcing the use of this daemon. Improper configuration may render the system non-functional. The "fapolicyd" API is not namespace aware and can cause issues when launching or running containers.

Satisfies: SRG-OS-000368-GPOS-00154, SRG-OS-000370-GPOS-00155, SRG-OS-000480-GPOS-00232

Check

Verify the RHEL 8 "fapolicyd" employs a deny-all, permit-by-exception policy.

Check that "fapolicyd" is in enforcement mode with the following command:

$ sudo grep permissive /etc/fapolicyd/fapolicyd.conf

permissive = 0

Check that fapolicyd employs a deny-all policy on system mounts with the following commands:

$ sudo tail /etc/fapolicyd/fapolicyd.rules

allow exe=/usr/bin/python3.7 : ftype=text/x-python
deny_audit perm=any pattern=ld_so : all
deny perm=any all : all

$ sudo cat /etc/fapolicyd/fapolicyd.mounts

/dev/shm
/run
/sys/fs/cgroup
/
/home
/boot
/run/user/42
/run/user/1000

If fapolicyd is not running in enforcement mode on all system mounts with a deny-all, permit-by-exception policy, this is a finding.

Fix

Configure RHEL 8 to employ a deny-all, permit-by-exception application whitelisting policy with "fapolicyd" using the following command:

Note: Running this command requires a root shell

# mount | egrep '^tmpfs| ext4| ext3| xfs' | awk '{ printf "%s\n", $3 }' >> /etc/fapolicyd/fapolicyd.mounts

With the "fapolicyd" installed and enabled, configure the daemon to function in permissive mode until the whitelist 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 whitelist in the "/etc/fapolicyd/fapolicyd.rules" file ensuring the last rule is "deny perm=any all : all".

Once it is determined the whitelist is built correctly, set the fapolicyd to enforcing mode by editing the "permissive" line in the /etc/fapolicyd/fapolicyd.conf file.

permissive = 0