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1.8.4 Ensure GDM automount is configured
Information
By default GNOME automatically mounts removable media when inserted as a convenience to the user.By using the lockdown mode in dconf, you can prevent users from changing specific settings.
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.
Without locking down the system settings, user settings take precedence over the system settings.
Satisfies: SRG-OS-000114-GPOS-00059, SRG-OS-000378-GPOS-00163, SRG-OS-000480-GPOS-00227
Solution
- Create or edit the file /etc/dconf/profile/user and add the following lines if they do not exist:user-db:user
system-db:local
Example:
#!/usr/bin/env bash
{
l_dir="/etc/dconf/profile/"
[ ! -d "$l_dir" ] && mkdir /etc/dconf/profile/
! grep -Psq '^\h*user-db:user\b' "$l_dir/user" && \
printf '%s\n' "" "user-db:user" >> "$l_dir/user"
! grep -Psq '^\h*system-db:local\b' "$l_dir/user" && \
sed -ri '/^\s*user-db:user/a system-db:local' "$l_dir/user"
} <xhtml:ol start="2"> - Run the following command to create the /etc/dconf/db/local.d/ and /etc/dconf/db/local.d/locks/ directories if either does not exist:
# [ ! -d "/etc/dconf/db/local.d/locks/" ] && mkdir -p /etc/dconf/db/local.d/locks/ <xhtml:ol start="3"> - Create or edit a file in /etc/dconf/db/local.d/locks/ and add the following lines:
/org/gnome/desktop/media-handling/automount
/org/gnome/desktop/media-handling/automount-open
Example:
# printf '%s\n' "" "/org/gnome/desktop/media-handling/automount" \
"/org/gnome/desktop/media-handling/automount-open" >> \
/etc/dconf/db/local.d/locks/60-media-automount <xhtml:ol start="4"> - Run the following script to comment out any incorrect settings in a local system-wide database keyfile:
#!/usr/bin/env bash
{
f_key_file_fix()
{
while IFS= read -r -d $'\0' l_file; do
grep -Psiq -- "^\h*$l_parameter$l_value(\b|\h*$)" "$l_file" && \
sed -ri '/^\s*'"$l_parameter"'/s/^/# /g' "$l_file"
done < <(find /etc/dconf/db -mindepth 2 -maxdepth 2 -type f -print0)
}
l_parameter="automount=" l_value="true"; f_key_file_fix
l_parameter="automount-open=" l_value="true"; f_key_file_fix
} <xhtml:ol start="5"> - Create or edit a local keyfile for machine-wide settings in '/etc/dconf/db/local.d/` with the following lines:
[org/gnome/desktop/media-handling]
automount=false
automount-open=false
Example script:
#!/usr/bin/env bash
{
l_file="/etc/dconf/db/local.d/60-media-automount"
a_keyfile=("[org/gnome/desktop/media-handling]" "automount=false" "automount-open=false")
if grep -Psq -- '^\h*\[org\/gnome\/desktop\/media-handling\]' "$l_file"; then
! grep -Psiq -- '^\h*automount-open=false\b' "$l_file" && \
sed -ri '/^\s*\[org\/gnome\/desktop\/media-handling\]/a automount-open=false' "$l_file"
! grep -Psiq -- '^\h*automount=false\b' "$l_file" && \
sed -ri '/^\s*\[org\/gnome\/desktop\/media-handling\]/a automount=false' "$l_file"
grep -Psiq -- '^\h*automount=true\b' "$l_file" && \
sed -ri 's/^\s*(automount=)(true).*$/\1fales/' "$l_file"
grep -Psiq -- '^\h*automount-open=true\b' "$l_file" && \
sed -ri 's/^\s*(automount-open=)(true).*$/\1fales/' "$l_file"
else
printf '%s\n' "" "${a_keyfile[@]}" >> "$l_file"
fi
} <xhtml:ol start="6"> - Run the following command to update the dconf databases:
# dconf update
Note: Users must log out and back in again before the system-wide settings take effect.
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
Item Details
Audit Name: CIS Rocky Linux 8 v3.0.0 L2 Workstation
Category: MEDIA PROTECTION
References: 800-53|MP-7, CSCv7|8.5
Plugin: Unix
Control ID: 17a2e210f80e0bfd13243bcd41b0868c2419e49c844a68746fbf97b42d6bb9b6