Disable Mounting of cramfs
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Description
To configure the system to prevent the cramfs
kernel module from being loaded, add the following line to the file /etc/modprobe.d/cramfs.conf
:
install cramfs /bin/false
This effectively prevents usage of this uncommon filesystem.
The cramfs
filesystem type is a compressed read-only
Linux filesystem embedded in small footprint systems. A
cramfs
image can be used without having to first
decompress the image.
Rationale
Removing support for unneeded filesystem types reduces the local attack surface
of the server.
Shell script
The following script can be run on the host to remediate the issue.
#!/bin/bash
# Remediation is applicable only in certain platforms
if dpkg-query --show --showformat='${db:Status-Status}
' 'kernel' 2>/dev/null | grep -q installed; then
if LC_ALL=C grep -q -m 1 "^install cramfs" /etc/modprobe.d/cramfs.conf ; then
sed -i 's#^install cramfs.*#install cramfs /bin/false#g' /etc/modprobe.d/cramfs.conf
else
echo -e "\n# Disable per security requirements" >> /etc/modprobe.d/cramfs.conf
echo "install cramfs /bin/false" >> /etc/modprobe.d/cramfs.conf
fi
if ! LC_ALL=C grep -q -m 1 "^blacklist cramfs$" /etc/modprobe.d/cramfs.conf ; then
echo "blacklist cramfs" >> /etc/modprobe.d/cramfs.conf
fi
else
>&2 echo 'Remediation is not applicable, nothing was done'
fi
Ansible playbook
The following playbook can be run with Ansible to remediate the issue.
- name: Gather the package facts
package_facts:
manager: auto
tags:
- NIST-800-171-3.4.6
- NIST-800-53-CM-6(a)
- NIST-800-53-CM-7(a)
- NIST-800-53-CM-7(b)
- disable_strategy
- kernel_module_cramfs_disabled
- low_complexity
- low_severity
- medium_disruption
- reboot_required
- name: Ensure kernel module 'cramfs' is disabled
lineinfile:
create: true
dest: /etc/modprobe.d/cramfs.conf
regexp: install\s+cramfs
line: install cramfs /bin/false
when: '"kernel" in ansible_facts.packages'
tags:
- NIST-800-171-3.4.6
- NIST-800-53-CM-6(a)
- NIST-800-53-CM-7(a)
- NIST-800-53-CM-7(b)
- disable_strategy
- kernel_module_cramfs_disabled
- low_complexity
- low_severity
- medium_disruption
- reboot_required
- name: Ensure kernel module 'cramfs' is blacklisted
lineinfile:
create: true
dest: /etc/modprobe.d/cramfs.conf
regexp: ^blacklist cramfs$
line: blacklist cramfs
when: '"kernel" in ansible_facts.packages'
tags:
- NIST-800-171-3.4.6
- NIST-800-53-CM-6(a)
- NIST-800-53-CM-7(a)
- NIST-800-53-CM-7(b)
- disable_strategy
- kernel_module_cramfs_disabled
- low_complexity
- low_severity
- medium_disruption
- reboot_required