cis-ubuntu1804-v220-1-5-2

1.5.2 Ensure core dumps are restricted (Automated)

Profile Applicability

• Level 1 - Server
• Level 1 - Workstation

Description

A core dump is the memory of an executable program. It is generally used to determine why a program aborted. It can also be used to glean confidential information from a core file. The system provides the ability to set a soft limit for core dumps, but this can be overridden by the user.

Rationale

Setting a hard limit on core dumps prevents users from overriding the soft variable. If core dumps are required, consider setting limits for user groups (see limits.conf(5)). In addition, setting the fs.suid_dumpable variable to 0 will prevent setuid programs from dumping core.

Audit Procedure

Command Line

Run the following command and verify output matches:

grep -Es '^(\*|\s).*hard.*core.*(\s+#.*)?
#x27; /etc/security/limits.conf /etc/security/limits.d/*

Run the following script to verify fs.suid_dumpable = 0:

#!/usr/bin/env bash
{
    l_output="" l_output2=""
    a_parlist=("fs.suid_dumpable=0")
    l_ufwscf="$([ -f /etc/default/ufw ] && awk -F= '/^\s*IPT_SYSCTL=/ {print $2}' /etc/default/ufw)"
    a_searchpath=("/run/sysctl.d/" "/etc/sysctl.d/" "/usr/local/lib/sysctl.d/" "/usr/lib/sysctl.d/" "/lib/sysctl.d/")
    unset A_files
    declare -A A_files
    A_files+=(["sysctl.conf"]="/etc/sysctl.conf")
    for l_searchpath in "${a_searchpath[@]}"; do
        if [ -d "$l_searchpath" ]; then
            while IFS= read -r -d 
#x27;\0' l_filename; do
                if [ -f "$l_filename" ]; then
                    l_basename="$(basename "$l_filename")"
                    if [ -z "${A_files["$l_basename"]}" ]; then
                        A_files+=(["$l_basename"]="$l_filename")
                    fi
                fi
            done < <(find "$l_searchpath" -type f -name '*.conf' -print0)
        fi
    done
    a_sorted=()
    while IFS= read -rd '' l_key; do
        a_sorted+=( "$l_key" )
    done < <(printf '%s\0' "${!A_files[@]}" | sort -rz)
    kernel_parameter_chk()
    {
        l_var="" l_var2=""
        l_krp="$(sysctl "$l_kpname" | awk -F= '{print $2}' | xargs)"
        if [ "$l_krp" = "$l_kpvalue" ]; then
            l_output="$l_output\n - \"$l_kpname\" is correctly set to \"$l_krp\" in the running configuration"
        else
            l_output2="$l_output2\n - \"$l_kpname\" is incorrectly set to \"$l_krp\" in the running configuration and should have a value of: \"$l_kpvalue\""
        fi
    }
    while IFS="=" read -r l_kpname l_kpvalue; do
        l_kpname="${l_kpname// /}"; l_kpvalue="${l_kpvalue// /}"
        kernel_parameter_chk
    done < <(printf '%s\n' "${a_parlist[@]}")
    unset A_files; unset a_sorted
    if [ -z "$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
}

Run the following command to check if systemd-coredump is installed:

systemctl is-enabled coredump.service

If enabled, masked, or disabled is returned systemd-coredump is installed.

Expected Result

* hard core 0

Remediation

Command Line

Add the following line to /etc/security/limits.conf or a /etc/security/limits.d/* file:

* hard core 0

Set the following parameter in /etc/sysctl.conf or a file in /etc/sysctl.d/ ending in .conf:

• fs.suid_dumpable = 0

Example:

printf '%s\n' "fs.suid_dumpable = 0" >> /etc/sysctl.d/60-fs_sysctl.conf

Run the following command to set the active kernel parameter:

sysctl -w fs.suid_dumpable=0

Note: If these settings appear in a conically later file, or later in the same file, these settings will be overwritten.

IF systemd-coredump is installed: edit /etc/systemd/coredump.conf and add/modify the following lines:

Storage=none
ProcessSizeMax=0

Run the command:

systemctl daemon-reload

References

1. NIST SP 800-53 Rev. 5: CM-6

CIS Controls

MITRE ATT&CK Mappings