Add noexec Option to /var/tmp

An XCCDF Rule

Description

The noexec mount option can be used to prevent binaries from being executed out of /var/tmp. Add the noexec option to the fourth column of /etc/fstab for the line which controls mounting of /var/tmp.

Rationale

Allowing users to execute binaries from world-writable directories such as /var/tmp should never be necessary in normal operation and can expose the system to potential compromise.

ID: xccdf_org.ssgproject.content_rule_mount_option_var_tmp_noexec
Severity: Medium
References: CCI-001764

SRG-OS-000368-GPOS-00154

1.1.3.5.4

R28

SV-230522r958804_rule
Updated: over 1 year ago

Remediation Templates

part /var/tmp --mountoptions="noexec"

- name: Gather the package facts
  package_facts:
    manager: auto
  tags:
  - DISA-STIG-RHEL-08-040134
  - configure_strategy  - high_disruption
  - low_complexity
  - medium_severity
  - mount_option_var_tmp_noexec
  - no_reboot_needed
- name: 'Add noexec Option to /var/tmp: Check information associated to mountpoint'
  command: findmnt --fstab '/var/tmp'
  register: device_name
  failed_when: device_name.rc > 1
  changed_when: false
  when:
  - ( not ( "kernel" in ansible_facts.packages and "rpm-ostree" in ansible_facts.packages
    and "bootc" in ansible_facts.packages ) and not ( ansible_virtualization_type
    in ["docker", "lxc", "openvz", "podman", "container"] ) )
  - '"/var/tmp" in ansible_mounts | map(attribute="mount") | list'
  tags:
  - DISA-STIG-RHEL-08-040134
  - configure_strategy
  - high_disruption
  - low_complexity
  - medium_severity
  - mount_option_var_tmp_noexec
  - no_reboot_needed

- name: 'Add noexec Option to /var/tmp: Create mount_info dictionary variable'
  set_fact:
    mount_info: '{{ mount_info|default({})|combine({item.0: item.1}) }}'
  with_together:
  - '{{ device_name.stdout_lines[0].split() | list | lower }}'
  - '{{ device_name.stdout_lines[1].split() | list }}'
  when:
  - ( not ( "kernel" in ansible_facts.packages and "rpm-ostree" in ansible_facts.packages
    and "bootc" in ansible_facts.packages ) and not ( ansible_virtualization_type
    in ["docker", "lxc", "openvz", "podman", "container"] ) )
  - '"/var/tmp" in ansible_mounts | map(attribute="mount") | list'
  - device_name.stdout is defined and device_name.stdout_lines is defined
  - (device_name.stdout | length > 0)
  tags:
  - DISA-STIG-RHEL-08-040134
  - configure_strategy
  - high_disruption
  - low_complexity
  - medium_severity
  - mount_option_var_tmp_noexec
  - no_reboot_needed

- name: 'Add noexec Option to /var/tmp: If /var/tmp not mounted, craft mount_info
    manually'
  set_fact:
    mount_info: '{{ mount_info|default({})|combine({item.0: item.1}) }}'
  with_together:
  - - target
    - source
    - fstype
    - options
  - - /var/tmp
    - ''
    - ''
    - defaults
  when:
  - ( not ( "kernel" in ansible_facts.packages and "rpm-ostree" in ansible_facts.packages
    and "bootc" in ansible_facts.packages ) and not ( ansible_virtualization_type
    in ["docker", "lxc", "openvz", "podman", "container"] ) )
  - '"/var/tmp" in ansible_mounts | map(attribute="mount") | list'
  - ("--fstab" | length == 0)
  - device_name.stdout is defined and device_name.stdout_lines is defined
  - (device_name.stdout | length == 0)
  tags:
  - DISA-STIG-RHEL-08-040134
  - configure_strategy
  - high_disruption
  - low_complexity
  - medium_severity
  - mount_option_var_tmp_noexec
  - no_reboot_needed

- name: 'Add noexec Option to /var/tmp: Make sure noexec option is part of the to
    /var/tmp options'
  set_fact:
    mount_info: '{{ mount_info | combine( {''options'':''''~mount_info.options~'',noexec''
      }) }}'
  when:
  - ( not ( "kernel" in ansible_facts.packages and "rpm-ostree" in ansible_facts.packages
    and "bootc" in ansible_facts.packages ) and not ( ansible_virtualization_type
    in ["docker", "lxc", "openvz", "podman", "container"] ) )
  - '"/var/tmp" in ansible_mounts | map(attribute="mount") | list'
  - mount_info is defined and "noexec" not in mount_info.options
  tags:
  - DISA-STIG-RHEL-08-040134
  - configure_strategy
  - high_disruption
  - low_complexity
  - medium_severity
  - mount_option_var_tmp_noexec
  - no_reboot_needed

- name: 'Add noexec Option to /var/tmp: Ensure /var/tmp is mounted with noexec option'
  mount:
    path: /var/tmp
    src: '{{ mount_info.source }}'
    opts: '{{ mount_info.options }}'
    state: mounted
    fstype: '{{ mount_info.fstype }}'
  when:
  - ( not ( "kernel" in ansible_facts.packages and "rpm-ostree" in ansible_facts.packages
    and "bootc" in ansible_facts.packages ) and not ( ansible_virtualization_type
    in ["docker", "lxc", "openvz", "podman", "container"] ) )
  - '"/var/tmp" in ansible_mounts | map(attribute="mount") | list'
  - mount_info is defined
  - (device_name.stdout is defined and (device_name.stdout | length > 0)) or ("--fstab"
    | length == 0)
  tags:
  - DISA-STIG-RHEL-08-040134
  - configure_strategy
  - high_disruption
  - low_complexity
  - medium_severity
  - mount_option_var_tmp_noexec
  - no_reboot_needed

# Remediation is applicable only in certain platforms
if ( ! ( { rpm --quiet -q kernel ;} && { rpm --quiet -q rpm-ostree ;} && { rpm --quiet -q bootc ;} ) && ! ( [ -f /.dockerenv ] || [ -f /run/.containerenv ] ) ) && { findmnt --kernel "/var/tmp" > /dev/null || findmnt --fstab "/var/tmp" > /dev/null; }; then
function perform_remediation {
    
        # the mount point /var/tmp has to be defined in /etc/fstab
        # before this remediation can be executed. In case it is not defined, the        # remediation aborts and no changes regarding the mount point are done.
        mount_point_match_regexp="$(printf "^[[:space:]]*[^#].*[[:space:]]%s[[:space:]]" "/var/tmp")"

    grep "$mount_point_match_regexp" -q /etc/fstab \
        || { echo "The mount point '/var/tmp' is not even in /etc/fstab, so we can't set up mount options" >&2;
                echo "Not remediating, because there is no record of /var/tmp in /etc/fstab" >&2; return 1; }
    


    mount_point_match_regexp="$(printf "^[[:space:]]*[^#].*[[:space:]]%s[[:space:]]" /var/tmp)"

    # 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 $4}' \
                    | sed -E "s/(rw|defaults|seclabel|noexec)(,|$)//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=""
        if [  "$fs_type" == "iso9660" ] ; then
            previous_mount_opts=$(sed 's/blocksize=/block=/' <<< "$previous_mount_opts")
        fi
        echo " /var/tmp  defaults,${previous_mount_opts}noexec 0 0" >> /etc/fstab
    # If the mount_opt option is not already in the mount point's /etc/fstab entry, add it
    elif ! grep "$mount_point_match_regexp" /etc/fstab | grep -q "noexec"; then
        previous_mount_opts=$(grep "$mount_point_match_regexp" /etc/fstab | awk '{print $4}')
        sed -i "s|\(${mount_point_match_regexp}.*${previous_mount_opts}\)|\1,noexec|" /etc/fstab
    fi


    if mkdir -p "/var/tmp"; then
        if mountpoint -q "/var/tmp"; then
            mount -o remount --target "/var/tmp"
        fi
    fi
}

perform_remediation

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

Add noexec Option to /var/tmp

Description

Rationale

Remediation Templates

Anaconda Pre-Install Instructions

An Ansible Snippet

A Shell Script