TMAegis
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Linux distributions

TMA-ROCKY8-5.1.5

Ensure access to SSH public host key files is configured

MediumLevel 1Automatedlinux

Description

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.

How it is checked

Audit method: Shell command

shell
alt0() { o=$(bash -c '#!/usr/bin/env bash

{
   a_output=(); a_output2=()
   l_pmask="0133"; l_maxperm="$( printf '"'"'%o'"'"' $(( 0777 & ~$l_pmask )) )"
   f_file_chk()
   {
      while IFS=: read -r l_file_mode l_file_owner l_file_group; do
         a_out2=()
         if [ $(( $l_file_mode & $l_pmask )) -gt 0 ]; then
            a_out2+=("    Mode: \"$l_file_mode\" should be mode: \"$l_maxperm\" or more restrictive")
         fi
         if [ "$l_file_owner" != "root" ]; then
            a_out2+=("    Owned by: \"$l_file_owner\" should be owned by: \"root\"")
         fi
         if [ "$l_file_group" != "root" ]; then
            a_out2+=("    Owned by group \"$l_file_group\" should be group owned by group: \"root\"")
         fi
         if [ "${#a_out2[@]}" -gt "0" ]; then
            a_output2+=("  - File: \"$l_file\"" "${a_out2[@]}")
         else
            a_output+=("  - File: \"$l_file\"" \
            "    Correct: mode: \"$l_file_mode\", owner: \"$l_file_owner\" and group owner: \"$l_file_group\" configured")
         fi
      done < <(stat -Lc '"'"'%#a:%U:%G'"'"' "$l_file")
   }
   while IFS= read -r -d $'"'"'\0'"'"' l_file; do
      if ssh-keygen -lf &>/dev/null "$l_file"; then
         file "$l_file" | grep -Piq -- '"'"'\bopenssh\h+([^#\n\r]+\h+)?public\h+key\b'"'"' && f_file_chk
      fi
   done < <(find -L /etc/ssh -xdev -type f -print0 2>/dev/null)
   if [ "${#a_output2[@]}" -le 0 ]; then
      [ "${#a_output[@]}" -le 0 ] && a_output+=("  - No openSSH public keys found")
      printf '"'"'%s\n'"'"' "" "- Audit Result:" "  ** PASS **" "${a_output[@]}" ""
   else
      printf '"'"'%s\n'"'"' "" "- Audit Result:" "  ** FAIL **" " - Reason(s) for audit failure:" "${a_output2[@]}"
      [ "${#a_output[@]}" -gt 0 ] && printf '"'"'%s\n'"'"' "" "- Correctly set:" "${a_output[@]}" ""
   fi
}' 2>&1); printf '%s\n' "$o" | grep -q '\*\* PASS \*\*' || { echo "step1: script did not report PASS"; return 1; }; }; if alt0; then echo compliant; fi
Expected output
compliant

How it is fixed

Fix method: Guidance or infrastructure patch

Run the following script to set mode, ownership, and group on the public SSH host key files: #!/usr/bin/env bash { a_output=(); a_output2=() l_pmask="0133"; l_maxperm="$( printf '%o' $(( 0777 & ~$l_pmask )) )" f_file_access_fix() { while IFS=: read -r l_file_mode l_file_owner l_file_group; do a_out2=() [ $(( $l_file_mode & $l_pmask )) -gt 0 ] && \ a_out2+=(" Mode: \"$l_file_mode\" should be mode: \"$l_maxperm\" or more restrictive" \ " updating to mode: \"$l_maxperm\"") && chmod u-x,go-wx "$l_file" [ "$l_file_owner" != "root" ] && \ a_out2+=(" Owned by: \"$l_file_owner\" should be owned by \"root\"" \ " Changing ownership to \"root\"") && chown root "$l_file" [ "$l_file_group" != "root" ] &&…

Properties

Operating systems
rocky-8
Tags
cis-convertedlinux
Reference
CIS Rocky Linux 8 Benchmark v3.0.0 - 5.1.5

Check this host

Run this on a machine you are allowed to audit. The scan is read-only.

shell
tmaegis scan --target linux