SV-258006r1045071: RHEL 9 SSH daemon must not allow known hosts authentication. | Red Hat Enterprise Linux 9 STIG SCAP Benchmark

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Assessment Title

Rule Text

RHEL 9 SSH daemon must not allow known hosts authentication.

Description

Discussion Text

Configuring the IgnoreUserKnownHosts setting for the SSH daemon provides additional assurance that remote login via SSH will require a password, even in the event of misconfiguration elsewhere.

How this relates to the STIG checklist: STIG vs SCAP benchmark.

IA Controls

NIST SP 800-53

Not mappedCCI-000366

References

DPMS Target Red Hat Enterprise Linux 9 DISA DPMS Target Red Hat Enterprise Linux 9 5551

SCC Automation Reference

The reconstructed evaluation script behind this rule's OVAL check(s) — every module a compound check combines, with this rule's own concrete values and DISA's SCC tool's real per-module mechanism curated from static teardown of SCC releases.

#!/bin/bash
# Reconstructed from oval:mil.disa.stig.rhel9os:def:258006
# RHEL 9 SSH daemon must not allow known hosts authentication.
# Per-module read mechanism curated from static teardown of DISA's SCC tool
# (SCAP Compliance Checker) -- see the SCC Automation Reference above.

# /etc/ssh/sshd_config:IgnoreUserKnownHosts == yes
# textfilecontent54_object (textfilecontent54_test)
test_1() {
  (sed -En 's/^\s*(?i)IgnoreUserKnownHosts(?-i)[ \t]+([\w\"]+)[\s]*(?:|(?:#.*))?$/\1/p' '/etc/ssh/sshd_config') | grep -Pq '^(yes|"yes")$'
}
# /etc/ssh/sshd_config includes sshd_config.d
# textfilecontent54_object (textfilecontent54_test)
test_2() {
  (sed -En 's/^\s*include\s+(.*)\s*$/\1/p' '/etc/ssh/sshd_config') | grep -qxF '/etc/ssh/sshd_config.d/*.conf'
}
# /etc/ssh/sshd_config.d:IgnoreUserKnownHosts == yes
# textfilecontent54_object (textfilecontent54_test)
test_3() {
  (grep -rhP --include='*.conf' '^\s*(?i)IgnoreUserKnownHosts(?-i)[ \t]+([\w\"]+)[\s]*(?:|(?:#.*))?$' '/etc/ssh/sshd_config.d' | sed -En 's/^\s*(?i)IgnoreUserKnownHosts(?-i)[ \t]+([\w\"]+)[\s]*(?:|(?:#.*))?$/\1/p') | grep -Pq '^(yes|"yes")$'
}

if ( test_1 || ( test_2 && test_3 ) ); then
  echo "PASS"
else
  echo "FAIL"
fi

Assessment Script Powered by AISandbox-executed

A standalone Shell script to assess this control automatically. Review before running it in your environment.

Syntax-checked and actually executed in an isolated sandbox (not the real system this checks) — confirmed to run without errors.

#!/bin/sh
# OVAL Definition: oval:mil.disa.stig.rhel9os:def:258006

if grep -qE '^\\s*(?i)IgnoreUserKnownHosts(?-i)[ \\t]+=[ \\t]+(yes|"yes")$' /etc/ssh/sshd_config || \
   grep -qE '^\\s*(?i)IgnoreUserKnownHosts(?-i)[ \\t]+=[ \\t]+(yes|"yes")$' /etc/ssh/sshd_config.d/*.conf; then
    echo "PASS"
    exit 0
else
    echo "FAIL"
    exit 1
fi

Remediation

Configure the SSH daemon to not allow known hosts authentication.

Add the following line to "/etc/ssh/sshd_config" or to a file in "/etc/ssh/sshd_config.d", or uncomment the line and set the value to "yes":

IgnoreUserKnownHosts yes

The SSH service must be restarted for changes to take effect:

$ sudo systemctl restart sshd.service