Mount Remote Filesystems with Kerberos Security

An XCCDF Rule

Description

Add the sec=krb5:krb5i:krb5p option to the fourth column of /etc/fstab for the line which controls mounting of any NFS mounts.

Rationale

When an NFS server is configured to use AUTH_SYS a selected userid and groupid are used to handle requests from the remote user. The userid and groupid could mistakenly or maliciously be set incorrectly. The AUTH_GSS method of authentication uses certificates on the server and client systems to more securely authenticate the remote mount request.

ID: xccdf_org.ssgproject.content_rule_mount_option_krb_sec_remote_filesystems
Severity: Medium
References: 1 12 14 15 16 18 3 5

DSS05.04 DSS05.10 DSS06.10

CCI-000366

4.3.3.6.1 4.3.3.6.2 4.3.3.6.3 4.3.3.6.4 4.3.3.6.5 4.3.3.6.6 4.3.3.6.7 4.3.3.6.8 4.3.3.6.9 4.3.3.7.3

SR 1.1 SR 1.10 SR 1.2 SR 1.5 SR 1.7 SR 1.8 SR 1.9 SR 2.1

A.18.1.4 A.6.1.2 A.9.1.2 A.9.2.1 A.9.2.3 A.9.2.4 A.9.3.1 A.9.4.1 A.9.4.2 A.9.4.3 A.9.4.4 A.9.4.5

AC-17(a) CM-6(a) CM-7(a) CM-7(b) IA-2 IA-2(8) IA-2(9)

PR.AC-4 PR.AC-7

SRG-OS-000480-GPOS-00227
Updated: about 1 year ago

# Remediation is applicable only in certain platforms
if [ ! -f /.dockerenv ] && [ ! -f /run/.containerenv ]; then

vfstype_points=()
readarray -t vfstype_points < <(grep -E "[[:space:]]nfs[4]?[[:space:]]" /etc/fstab | awk '{print $2}')
for vfstype_point in "${vfstype_points[@]}"
do
    mount_point_match_regexp="$(printf "^[[:space:]]*[^#].*[[:space:]]%s[[:space:]]" ${vfstype_point//\\/\\\\})"

    # If the mount point is not in /etc/fstab, get previous mount options from /etc/mtab
    if ! grep -q "$mount_point_match_regexp" /etc/fstab; then
        # runtime opts without some automatic kernel/userspace-added defaults
        previous_mount_opts=$(grep "$mount_point_match_regexp" /etc/mtab | head -1 |  awk '{print $4}' \
                    | sed -E "s/(rw|defaults|seclabel|sec=krb5:krb5i:krb5p)(,|$)//g;s/,$//")
        [ "$previous_mount_opts" ] && previous_mount_opts+=","
        # In iso9660 filesystems mtab could describe a "blocksize" value, this should be reflected in
        # fstab as "block".  The next variable is to satisfy shellcheck SC2050.
        fs_type="nfs4"
        if [  "$fs_type" == "iso9660" ] ; then
            previous_mount_opts=$(sed 's/blocksize=/block=/' <<< "$previous_mount_opts")
        fi
        echo " ${vfstype_point//\\/\\\\} nfs4 defaults,${previous_mount_opts}sec=krb5:krb5i:krb5p 0 0" >> /etc/fstab
    # If the mount_opt option is not already in the mount point's /etc/fstab entry, add it
    elif ! grep "$mount_point_match_regexp" /etc/fstab | grep -q "sec=krb5:krb5i:krb5p"; then
        previous_mount_opts=$(grep "$mount_point_match_regexp" /etc/fstab | awk '{print $4}')
        sed -i "s|\(${mount_point_match_regexp}.*${previous_mount_opts}\)|\1,sec=krb5:krb5i:krb5p|" /etc/fstab
    fi
done

else
    >&2 echo 'Remediation is not applicable, nothing was done'
fi

- name: Get nfs and nfs4 mount points, that don't have sec=krb5:krb5i:krb5p
  command: findmnt --fstab --types nfs,nfs4 -O nosec=krb5:krb5i:krb5p -n -P
  register: points_register
  check_mode: false
  changed_when: false
  failed_when: false  when: ansible_virtualization_type not in ["docker", "lxc", "openvz", "podman", "container"]
  tags:
  - NIST-800-53-AC-17(a)
  - NIST-800-53-CM-6(a)
  - NIST-800-53-CM-7(a)
  - NIST-800-53-CM-7(b)
  - NIST-800-53-IA-2
  - NIST-800-53-IA-2(8)
  - NIST-800-53-IA-2(9)
  - configure_strategy
  - low_complexity
  - medium_disruption
  - medium_severity
  - mount_option_krb_sec_remote_filesystems
  - no_reboot_needed

- name: Add sec=krb5:krb5i:krb5p to nfs and nfs4 mount points
  mount:
    path: '{{ item | regex_search(''TARGET="([^"]+)"'',''\1'') | first }}'
    src: '{{ item | regex_search(''SOURCE="([^"]+)"'',''\1'') | first }}'
    fstype: '{{ item | regex_search(''FSTYPE="([^"]+)"'',''\1'') | first }}'
    state: present
    opts: '{{ item | regex_search(''OPTIONS="([^"]+)"'',''\1'') | first }},sec=krb5:krb5i:krb5p'
  when:
  - ansible_virtualization_type not in ["docker", "lxc", "openvz", "podman", "container"]
  - (points_register.stdout | length > 0) and '\\x09' not in item
  with_items: '{{ points_register.stdout_lines }}'
  tags:
  - NIST-800-53-AC-17(a)
  - NIST-800-53-CM-6(a)
  - NIST-800-53-CM-7(a)
  - NIST-800-53-CM-7(b)
  - NIST-800-53-IA-2
  - NIST-800-53-IA-2(8)
  - NIST-800-53-IA-2(9)
  - configure_strategy
  - low_complexity
  - medium_disruption
  - medium_severity
  - mount_option_krb_sec_remote_filesystems
  - no_reboot_needed

Mount Remote Filesystems with Kerberos Security

Description

Rationale

Remediation - Shell Script

Remediation - Ansible