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1.8.6 Ensure GDM automatic mounting of removable media is disabled

Information

By default GNOME automatically mounts removable media when inserted as a convenience to the user.

With automounting enabled anyone with physical access could attach a USB drive or disc and have its contents available in system even if they lacked permissions to mount it themselves.

Solution

Run the following script to disable automatic mounting of media for all GNOME users:

#!/usr/bin/env bash

{
 l_pkgoutput=""
 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

 # determine system's package manager
 if command -v dpkg-query > /dev/null 2>&1; then
 l_pq="dpkg-query -W"
 elif command -v rpm > /dev/null 2>&1; then
 l_pq="rpm -q"
 fi
 # Check if GDM is installed
 l_pcl="gdm gdm3" # Space seporated list of packages to check
 for l_pn in $l_pcl; do
 $l_pq "$l_pn" > /dev/null 2>&1 && l_pkgoutput="$l_pkgoutput
 - Package: \"$l_pn\" exists on the system
 - checking configuration"
 done
 # 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="$(grep -Prils -- '^h*automountb' /etc/dconf/db/*.d)"
 l_kfile2="$(grep -Prils -- '^h*automount-openb' /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 \"$l_gpname\""
 elif [ -f "$l_kfile2" ]; then
 l_gpname="$(awk -F/ '{split($(NF-1),a,".");print a[1]}' <<< "$l_kfile2")"
 echo " - updating dconf profile name to \"$l_gpname\""
 fi
 # check for consistency (Clean up configuration if needed)
 if [ -f "$l_kfile" ] &amp;&amp; [ "$(awk -F/ '{split($(NF-1),a,".");print a[1]}' <<< "$l_kfile")" != "$l_gpname" ]; then
 sed -ri "/^s*automounts*=/s/^/# /" "$l_kfile"
 l_kfile="/etc/dconf/db/$l_gpname.d/00-media-automount"
 fi
 if [ -f "$l_kfile2" ] &amp;&amp; [ "$(awk -F/ '{split($(NF-1),a,".");print a[1]}' <<< "$l_kfile2")" != "$l_gpname" ]; then
 sed -ri "/^s*automount-opens*=/s/^/# /" "$l_kfile2"
 fi
 [ -z "$l_kfile" ] &amp;&amp; l_kfile="/etc/dconf/db/$l_gpname.d/00-media-automount"
 # Check if profile file exists
 if grep -Pq -- "^h*system-db:$l_gpnameb" /etc/dconf/profile/*; then
 echo -e "
 - dconf database profile exists in: \"$(grep -Pl -- "^h*system-db:$l_gpnameb" /etc/dconf/profile/*)\""
 else
 if [ ! -f "/etc/dconf/profile/user" ]; then
 l_gpfile="/etc/dconf/profile/user"
 else
 l_gpfile="/etc/dconf/profile/user2"
 fi
 echo -e " - creating dconf database profile"
 {
 echo -e "
user-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 "$l_gpdir"
 fi
 # check automount-open setting
 if grep -Pqs -- '^h*automount-openh*=h*falseb' "$l_kfile"; then
 echo " - \"automount-open\" is set to false in: \"$l_kfile\""
 else
 echo " - creating \"automount-open\" entry in \"$l_kfile\""
 ! grep -Psq -- '^h*[org/gnome/desktop/media-handling]b' "$l_kfile" &amp;&amp; echo '[org/gnome/desktop/media-handling]' >> "$l_kfile"
 sed -ri '/^s*[org/gnome/desktop/media-handling]/a \nautomount-open=false' "$l_kfile"
 fi
 # check automount setting
 if grep -Pqs -- '^h*automounth*=h*falseb' "$l_kfile"; then
 echo " - \"automount\" is set to false in: \"$l_kfile\""
 else
 echo " - creating \"automount\" entry in \"$l_kfile\""
 ! grep -Psq -- '^h*[org/gnome/desktop/media-handling]b' "$l_kfile" &amp;&amp; echo '[org/gnome/desktop/media-handling]' >> "$l_kfile"
 sed -ri '/^s*[org/gnome/desktop/media-handling]/a \nautomount=false' "$l_kfile"
 fi
 # update dconf database
 dconf update
 else
 echo -e "
 - GNOME Desktop Manager package is not installed on the system
 - Recommendation is not applicable"
 fi
}

OR

Run the following command to uninstall the GNOME desktop Manager package:

# dnf remove gdm

Impact:

The use of portable hard drives is very common for workstation users. If your organization allows the use of portable storage or media on workstations and physical access controls to workstations is considered adequate there is little value add in turning off automounting.

See Also

https://workbench.cisecurity.org/benchmarks/15288

Item Details

Category: MEDIA PROTECTION

References: 800-53|MP-7, CSCv7|8.5

Plugin: Unix

Control ID: 650bb366de5f49dc84efb2509705698af3769e0fcad05eb193bb6c88ac9c6b7a