3.2.6 Ensure bluetooth kernel module is not available

Information

Bluetooth is a short-range wireless technology standard that is used for exchanging data between devices over short distances. It employs UHF radio waves in the ISM bands, from 2.402 GHz to 2.48 GHz. It is mainly used as an alternative to wire connections.

Without protection of communications with wireless peripherals, confidentiality and integrity may be compromised because unprotected communications can be intercepted and either read, altered, or used to compromise the operating system.

This requirement applies to wireless peripheral technologies (e.g., wireless mice, keyboards, displays, etc.) used with RHEL 8 operating systems. Wireless peripherals (e.g., Wi-Fi/Bluetooth/IR Keyboards, Mice, and Pointing Devices and Near Field Communications [NFC]) present a unique challenge by creating an open, unsecured port on a computer. Wireless peripherals must meet DoD requirements for wireless data transmission and be approved for use by the Authorizing Official (AO). Even though some wireless peripherals, such as mice and pointing devices, do not ordinarily carry information that need to be protected, modification of communications with these wireless peripherals may be used to compromise the operating system. Communication paths outside the physical protection of a controlled boundary are exposed to the possibility of interception and modification.

Protecting the confidentiality and integrity of communications with wireless peripherals can be accomplished by physical means (e.g., employing physical barriers to wireless radio frequencies) or by logical means (e.g., employing cryptographic techniques). If physical means of protection are employed, then logical means (cryptography) do not have to be employed, and vice versa. If the wireless peripheral is only passing telemetry data, encryption of the data may not be required.

Solution

Configure the operating system to disable the Bluetooth adapter when not in use.

Build or modify the "/etc/modprobe.d/bluetooth.conf" file with the following line:

install bluetooth /bin/true

Run the following script to unload and disable the bluetooth module:

- IF - the bluetooth kernel module is available in ANY installed kernel:

- Create a file ending in .conf with install bluetooth /bin/false in the /etc/modprobe.d/ directory
- Create a file ending in .conf with blacklist bluetooth in the /etc/modprobe.d/ directory
- Run modprobe -r bluetooth 2>/dev/null; rmmod bluetooth 2>/dev/null to remove bluetooth from the kernel

- IF - the bluetooth kernel module is not available on the system, or pre-compiled into the kernel, no remediation is necessary

#!/usr/bin/env bash

{
a_output2=() a_output3=() l_dl="" l_mod_name="bluetooth" l_mod_type="net"
l_mod_path="$(readlink -f /lib/modules/**/kernel/$l_mod_type | sort -u)"
f_module_fix()
{
l_dl="y" a_showconfig=()
while IFS= read -r l_showconfig; do
a_showconfig+=("$l_showconfig")
done < <(modprobe --showconfig | grep -P -- '\b(install|blacklist)\h+'"${l_mod_chk_name//-/_}"'\b')
if lsmod | grep "$l_mod_chk_name" &> /dev/null; then
a_output2+=(" - unloading kernel module: \"$l_mod_name\"")
modprobe -r "$l_mod_chk_name" 2>/dev/null; rmmod "$l_mod_name" 2>/dev/null
fi
if ! grep -Pq -- '\binstall\h+'"${l_mod_chk_name//-/_}"'\h+(\/usr)?\/bin\/(true|false)\b' <<< "${a_showconfig[*]}"; then
a_output2+=(" - setting kernel module: \"$l_mod_name\" to \"$(readlink -f /bin/false)\"")
printf '%s\n' "install $l_mod_chk_name $(readlink -f /bin/false)" >> /etc/modprobe.d/"$l_mod_name".conf
fi
if ! grep -Pq -- '\bblacklist\h+'"${l_mod_chk_name//-/_}"'\b' <<< "${a_showconfig[*]}"; then
a_output2+=(" - denylisting kernel module: \"$l_mod_name\"")
printf '%s\n' "blacklist $l_mod_chk_name" >> /etc/modprobe.d/"$l_mod_name".conf
fi
}
for l_mod_base_directory in $l_mod_path; do # Check if the module exists on the system
if [ -d "$l_mod_base_directory/${l_mod_name/-/\/}" ] && [ -n "$(ls -A "$l_mod_base_directory/${l_mod_name/-/\/}")" ]; then
a_output3+=(" - \"$l_mod_base_directory\"")
l_mod_chk_name="$l_mod_name"
[[ "$l_mod_name" =~ overlay ]] && l_mod_chk_name="${l_mod_name::-2}"
[ "$l_dl" != "y" ] && f_module_fix
else
printf '%s\n' " - kernel module: \"$l_mod_name\" doesn't exist in \"$l_mod_base_directory\""
fi
done
[ "${#a_output3[@]}" -gt 0 ] && printf '%s\n' "" " -- INFO --" " - module: \"$l_mod_name\" exists in:" "${a_output3[@]}"
[ "${#a_output2[@]}" -gt 0 ] && printf '%s\n' "" "${a_output2[@]}" || printf '%s\n' "" " - No changes needed"
printf '%s\n' "" " - remediation of kernel module: \"$l_mod_name\" complete" ""
}

Reboot the system for the settings to take effect.

Impact:

Many personal electronic devices (PEDs) use Bluetooth technology. For example, you may be able to operate your computer with a wireless keyboard. Disabling Bluetooth will prevent these devices from connecting to the system.

Item Details

Audit Name: CIS Red Hat Enterprise Linux 8 STIG v2.0.0 STIG

Category: ACCESS CONTROL

Plugin: Unix

Control ID: ebd3c7e0d8952f41bd2a2f91a4dfe43325a08c7325fb1f8e018cb9d1a6e789a6

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3.2.6 Ensure bluetooth kernel module is not available

Information

Solution

See Also

Item Details