Cis Ubuntu1804 V220 1 8 8

1.8.8 Ensure GDM autorun-never is enabled (Automated)

Profile Applicability

• Level 1 - Server
• Level 1 - Workstation

Description

The autorun-never setting allows the GNOME Desktop Display Manager to disable autorun through GDM.

Rationale

Malware on removable media may taking advantage of Autorun features when the media is inserted into a system and execute.

Audit Procedure

Command Line

Run the following script to verify that autorun-never is set to true for GDM:

#!/usr/bin/env bash

{
    l_pkgoutput="" l_output="" l_output2=""
    # Check if GNOME Desktop Manager is installed. If package isn't installed, recommendation is Not Applicable\n
    # determine system's package manager
    if command -v dpkg-query > /dev/null 2>&1; then
        l_pq="dpkg-query -s"
    elif command -v rpm > /dev/null 2>&1; then
        l_pq="rpm -q"
    fi
    # Check if GDM is installed
    l_pcl="gdm gdm3" # Space separated list of packages to check
    for l_pn in $l_pcl; do
        $l_pq "$l_pn" > /dev/null 2>&1 && l_pkgoutput="$l_pkgoutput\n - Package: \"$l_pn\" exists on the system\n - checking configuration"
    done
    echo -e "$l_pkgoutput"
    # Check configuration (If applicable)
    if [ -n "$l_pkgoutput" ]; then
        echo -e "$l_pkgoutput"
        # Look for existing settings and set variables if they exist
        l_kfile="$(grep -Prils -- '^\h*autorun-never\b' /etc/dconf/db/*.d)"
        # Set profile name based on dconf db directory ({PROFILE_NAME}.d)
        if [ -f "$l_kfile" ]; then
            l_gpname="$(awk -F\/ '{split($(NF-1),a,".");print a[1]}' <<< "$l_kfile")"
        fi
        # If the profile name exist, continue checks
        if [ -n "$l_gpname" ]; then
            l_gpdir="/etc/dconf/db/$l_gpname.d"
            # Check if profile file exists
            if grep -Pq -- "^\h*system-db:$l_gpname\b" /etc/dconf/profile/*; then
                l_output="$l_output\n - dconf database profile file \"$(grep -Pl -- "^\h*system-db:$l_gpname\b" /etc/dconf/profile/*)\" exists"
            else
                l_output2="$l_output2\n - dconf database profile isn't set"
            fi
            # Check if the dconf database file exists
            if [ -f "/etc/dconf/db/$l_gpname" ]; then
                l_output="$l_output\n - The dconf database \"$l_gpname\" exists"
            else
                l_output2="$l_output2\n - The dconf database \"$l_gpname\" doesn't exist"
            fi
            # check if the dconf database directory exists
            if [ -d "$l_gpdir" ]; then
                l_output="$l_output\n - The dconf directory \"$l_gpdir\" exitst"
            else
                l_output2="$l_output2\n - The dconf directory \"$l_gpdir\" doesn't exist"
            fi
            # check autorun-never setting
            if grep -Pqrs -- '^\h*autorun-never\h*=\h*true\b' "$l_kfile"; then
                l_output="$l_output\n - \"autorun-never\" is set to true in: \"$l_kfile\""
            else
                l_output2="$l_output2\n - \"autorun-never\" is not set correctly"
            fi
        else
            # Settings don't exist. Nothing further to check
            l_output2="$l_output2\n - \"autorun-never\" is not set"
        fi
    else
        l_output="$l_output\n - GNOME Desktop Manager package is not installed on the system\n  - Recommendation is not applicable"
    fi
    # Report results. If no failures output in l_output2, we pass
    if [ -z "$l_output2" ]; then
        echo -e "\n- Audit Result:\n  ** PASS **\n$l_output\n"
    else
        echo -e "\n- Audit Result:\n  ** FAIL **\n - Reason(s) for audit failure:\n$l_output2\n"
        [ -n "$l_output" ] && echo -e "\n- Correctly set:\n$l_output\n"
    fi
}

Remediation

Command Line

Run the following script to set autorun-never to true for GDM users:

#!/usr/bin/env bash

{
    l_pkgoutput="" l_output="" l_output2=""
    l_gpname="local" # Set to desired dconf profile name (default is local)
    # Check if GNOME Desktop Manager is installed. If package isn't installed, recommendation is Not Applicable\n
    # determine system's package manager
    if command -v dpkg-query > /dev/null 2>&1; then
        l_pq="dpkg-query -s"
    elif command -v rpm > /dev/null 2>&1; then
        l_pq="rpm -q"
    fi
    # Check if GDM is installed
    l_pcl="gdm gdm3" # Space separated list of packages to check
    for l_pn in $l_pcl; do
        $l_pq "$l_pn" > /dev/null 2>&1 && l_pkgoutput="$l_pkgoutput\n - Package: \"$l_pn\" exists on the system\n - checking configuration"
    done
    echo -e "$l_pkgoutput"
    # Check configuration (If applicable)
    if [ -n "$l_pkgoutput" ]; then
        echo -e "$l_pkgoutput"
        # Look for existing settings and set variables if they exist
        l_kfile="$(grep -Prils -- '^\h*autorun-never\b' /etc/dconf/db/*.d)"
        # Set profile name based on dconf db directory ({PROFILE_NAME}.d)
        if [ -f "$l_kfile" ]; then
            l_gpname="$(awk -F\/ '{split($(NF-1),a,".");print a[1]}' <<< "$l_kfile")"
            echo " - updating dconf profile name to \"$l_gpname\""
        fi
        [ ! -f "$l_kfile" ] && l_kfile="/etc/dconf/db/$l_gpname.d/00-media-autorun"
        # Check if profile file exists
        if grep -Pq -- "^\h*system-db:$l_gpname\b" /etc/dconf/profile/*; then
            echo -e "\n - dconf database profile exists in: \"$(grep -Pl -- "^\h*system-db:$l_gpname\b" /etc/dconf/profile/*)\""
        else
            [ ! -f "/etc/dconf/profile/user" ] && l_gpfile="/etc/dconf/profile/user" || l_gpfile="/etc/dconf/profile/user2"
            echo -e " - creating dconf database profile"
            {
                echo -e "\nuser-db:user"
                echo "system-db:$l_gpname"
            } >> "$l_gpfile"
        fi
        # create dconf directory if it doesn't exists
        l_gpdir="/etc/dconf/db/$l_gpname.d"
        if [ -d "$l_gpdir" ]; then
            echo " - The dconf database directory \"$l_gpdir\" exists"
        else
            echo " - creating dconf database directory \"$l_gpdir\""
            mkdir "$l_gpdir"
        fi
        # check autorun-never setting
        if grep -Pqs -- '^\h*autorun-never\h*=\h*true\b' "$l_kfile"; then
            echo " - \"autorun-never\" is set to true in: \"$l_kfile\""
        else
            echo " - creating or updating \"autorun-never\" entry in \"$l_kfile\""
            if grep -Psq -- '^\h*autorun-never' "$l_kfile"; then
                sed -ri 's/^\s*autorun-never\s*=\s*\S+/autorun-never=true' "$l_kfile"
            else
                ! grep -Psq -- '^\h*\[org\/gnome\/desktop\/media-handling\]\b' "$l_kfile" && echo '[org/gnome/desktop/media-handling]' >> "$l_kfile"
                sed -ri '/^\s*\[org\/gnome\/desktop\/media-handling\]/a \\nautorun-never=true' "$l_kfile"
            fi
        fi
    else
        echo -e "\n - GNOME Desktop Manager package is not installed on the system\n  - Recommendation is not applicable"
    fi
    # update dconf database
    dconf update
}

Default Value

false

References

1. NIST SP 800-53 Rev. 5: CM-1, CM-2, CM-6, CM-7, IA-5

CIS Controls

MITRE ATT&CK Mappings