cis-ubuntu1804-v220-1-1-1-3

Ensure mounting of jffs2 filesystems is disabled

Profile

Level 1 - Server / Level 1 - Workstation, Assessment: Automated

Description

The jffs2 (journaling flash filesystem 2) filesystem type is a log-structured filesystem used in flash memory devices.

Rationale

Removing support for unneeded filesystem types reduces the local attack surface of the system. If this filesystem type is not needed, disable it.

Impact

None noted.

Audit Procedure

Command Line

Run the following script to verify the jffs2 module is disabled. If the module is available in the running kernel:

• An entry including /bin/true or /bin/false exists in a file within the /etc/modprobe.d/ directory
• The module is deny listed in a file within the /etc/modprobe.d/ directory
• The module is not loaded in the kernel

If available in ANY installed kernel:

• The module is deny listed in a file within the /etc/modprobe.d/ directory

#!/usr/bin/env bash
{
    l_output="" l_output2="" l_output3="" l_dl=""
    l_mname="jffs2"
    l_mtype="fs"
    l_searchloc="/lib/modprobe.d/*.conf /usr/local/lib/modprobe.d/*.conf /run/modprobe.d/*.conf /etc/modprobe.d/*.conf"
    l_mpath="/lib/modules/**/kernel/$l_mtype"
    l_mpname="$(tr '-' ' ' <<< "$l_mname")"
    l_mndir="$(tr '-' '/' <<< "$l_mname")"

    module_loadable_chk()
    {
        l_loadable="$(modprobe -n -v "$l_mname")"
        [ "$(wc -l <<< "$l_loadable")" -gt "1" ] && l_loadable="$(grep -P -- "(^\h*install|\b$l_mname)\b" <<< "$l_loadable")"
        if grep -Pq -- '^\h*install \/bin\/(true|false)' <<< "$l_loadable"; then
            l_output="$l_output\n - module: \"$l_mname\" is not loadable: \"$l_loadable\""
        else
            l_output2="$l_output2\n - module: \"$l_mname\" is loadable: \"$l_loadable\""
        fi
    }
    module_loaded_chk()
    {
        if ! lsmod | grep "$l_mname" > /dev/null 2>&1; then
            l_output="$l_output\n - module: \"$l_mname\" is not loaded"
        else
            l_output2="$l_output2\n - module: \"$l_mname\" is loaded"
        fi
    }
    module_deny_chk()
    {
        l_dl="y"
        if modprobe --showconfig | grep -Pq -- '^\h*blacklist\h+'"$l_mpname"'\b'; then
            l_output="$l_output\n - module: \"$l_mname\" is deny listed in: \"$(grep -Pls -- "^\h*blacklist\h+$l_mname\b" $l_searchloc)\""
        else
            l_output2="$l_output2\n - module: \"$l_mname\" is not deny listed"
        fi
    }
    for l_mdir in $l_mpath; do
        if [ -d "$l_mdir/$l_mndir" ] && [ -n "$(ls -A $l_mdir/$l_mndir)" ]; then
            l_output3="$l_output3\n  - \"$l_mdir\""
            [ "$l_dl" != "y" ] && module_deny_chk
            if [ "$l_mdir" = "/lib/modules/$(uname -r)/kernel/$l_mtype" ]; then
                module_loadable_chk
                module_loaded_chk
            fi
        else
            l_output="$l_output\n - module: \"$l_mname\" doesn't exist in \"$l_mdir\""
        fi
    done
    [ -n "$l_output3" ] && echo -e "\n\n -- INFO --\n - module: \"$l_mname\" exists in:$l_output3"
    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
}

Expected Result

• module: "jffs2" is not loadable
• module: "jffs2" is not loaded
• module: "jffs2" is deny listed

Remediation

Command Line

If the module is available in the running kernel:

• Create a file with install jffs2 /bin/false in the /etc/modprobe.d/ directory
• Create a file with blacklist jffs2 in the /etc/modprobe.d/ directory
• Unload jffs2 from the kernel

If available in ANY installed kernel:

• Create a file with blacklist jffs2 in the /etc/modprobe.d/ directory

If the kernel module is not available on the system or pre-compiled into the kernel:

• No remediation is necessary

#!/usr/bin/env bash
{
    l_mname="jffs2"
    l_mtype="fs"
    l_mpath="/lib/modules/**/kernel/$l_mtype"
    l_mpname="$(tr '-' ' ' <<< "$l_mname")"
    l_mndir="$(tr '-' '/' <<< "$l_mname")"

    module_loadable_fix()
    {
        l_loadable="$(modprobe -n -v "$l_mname")"
        [ "$(wc -l <<< "$l_loadable")" -gt "1" ] && l_loadable="$(grep -P -- "(^\h*install|\b$l_mname)\b" <<< "$l_loadable")"
        if ! grep -Pq -- '^\h*install \/bin\/(true|false)' <<< "$l_loadable"; then
            echo -e "\n - setting module: \"$l_mname\" to be not loadable"
            echo -e "install $l_mname /bin/false" >> /etc/modprobe.d/"$l_mpname".conf
        fi
    }
    module_loaded_fix()
    {
        if lsmod | grep "$l_mname" > /dev/null 2>&1; then
            echo -e "\n - unloading module \"$l_mname\""
            modprobe -r "$l_mname"
        fi
    }
    module_deny_fix()
    {
        if ! modprobe --showconfig | grep -Pq -- "^\h*blacklist\h+$l_mpname\b"; then
            echo -e "\n - deny listing \"$l_mname\""
            echo -e "blacklist $l_mname" >> /etc/modprobe.d/"$l_mpname".conf
        fi
    }
    for l_mdir in $l_mpath; do
        if [ -d "$l_mdir/$l_mndir" ] && [ -n "$(ls -A $l_mdir/$l_mndir)" ]; then
            echo -e "\n - module: \"$l_mname\" exists in \"$l_mdir\"\n - checking if disabled..."
            module_deny_fix
            if [ "$l_mdir" = "/lib/modules/$(uname -r)/kernel/$l_mtype" ]; then
                module_loadable_fix
                module_loaded_fix
            fi
        else
            echo -e "\n - module: \"$l_mname\" doesn't exist in \"$l_mdir\"\n"
        fi
    done
    echo -e "\n - remediation of module: \"$l_mname\" complete\n"
}

Default Value

Not disabled by default.

References

1. NIST SP 800-53 Rev. 5: CM-7

CIS Controls

v8 - 4.8 Uninstall or Disable Unnecessary Services on Enterprise Assets and Software (IG 2, IG 3) v7 - 9.2 Ensure Only Approved Ports, Protocols and Services Are Running (IG 2, IG 3)

MITRE ATT&CK Mappings: T1005, T1005.000 (TA0005) - M1050