Detections
Analytics
4.2.3 Ensure permissions on SSH public host key files are configured
Information
An SSH public key is one of two files used in SSH public key authentication. In this authentication method, a public key is a key that can be used for verifying digital signatures generated using a corresponding private key. Only a public key that corresponds to a private key will be able to authenticate successfully.If a public host key file is modified by an unauthorized user, the SSH service may be compromised.
Solution
Run the following script to set mode, ownership, and group on the public SSH host key files:#!/usr/bin/env bash
{
l_output="" l_output2=""
l_skgn="$(grep -Po -- '^(ssh_keys|_?ssh)b' /etc/group)" # Group designated to own openSSH keys
l_skgid="$(awk -F: '($1 == "'"$l_skgn"'"){print $3}' /etc/group)" # Get gid of group
l_mfix="u-x,go-wx"
if command -v ssh-keygen &>/dev/null; then
unset a_skarr && a_skarr=() # Clear and initialize array
if [ -d /etc/ssh ]; then
while IFS= read -r -d $'0' l_file; do # Loop to populate array
if grep -Pq -- 'h+noh+commentb' <<< "$(ssh-keygen -l -f 2>/dev/null "$l_file")"; then
a_skarr+=("$(stat -Lc '%n^%#a^%U^%G^%g' "$l_file")")
fi
done < <(find -L /etc/ssh -xdev -type f -print0)
if (( ${#a_skarr[@]} > 0 )); then
while IFS="^" read -r l_file l_mode l_owner l_group l_gid; do
l_out2=""
l_pmask="0133"
l_maxperm="$( printf '%o' $(( 0777 & ~$l_pmask )) )"
if [ $(( $l_mode & $l_pmask )) -gt 0 ]; then
l_out2="$l_out2
- Mode: \"$l_mode\" should be mode: \"$l_maxperm\" or more restrictive
- Revoking excess permissions"
chmod "$l_mfix" "$l_file"
fi
if [ "$l_owner" != "root" ]; then
l_out2="$l_out2
- Owned by: \"$l_owner\" should be owned by \"root\"
- Changing ownership to \"root\""
chown root "$l_file"
fi
if [[ ! "$l_group" =~ $l_agroup ]]; then
l_out2="$l_out2
- Owned by group \"$l_group\" should be group owned by: \"${l_agroup//|/ or }\"
- Changing group ownership to \"$l_sgroup\""
chgrp "$l_sgroup" "$l_file"
fi
[ -n "$l_out2" ] && l_output2="$l_output2
- File: \"$l_file\"$l_out2"
done <<< "$(printf '%s
' "${a_skarr[@]}")"
else
l_output=" - No public keys found in \"/etc/ssh\""
fi
else
l_output="- ssh directory not found on the system"
fi
unset a_skarr
else
l_output2=" - ssh-keygen command not found
- manual remediation may be required"
fi
if [ -z "$l_output2" ]; then
echo -e "
- No access changes required
"
else
echo -e "
- Remediation results:
$l_output2
"
fi
}
See Also
Item Details
Audit Name: CIS Red Hat Enterprise Linux 7 v4.0.0 L1 Server
Category: ACCESS CONTROL, MEDIA PROTECTION
References: 800-53|AC-3, 800-53|AC-5, 800-53|AC-6, 800-53|MP-2, CSCv7|5.1
Plugin: Unix
Control ID: 96a700c6e6588a5bc12ab5f0ea0efe256c82bd45f3c849748fb28ab9505bc3a8