SV-204594r987796: The Red Hat Enterprise Linux operating system must be configured so that the SSH daemon is configured to only use the SSHv2 protocol. | Red Hat Enterprise Linux 7 STIG SCAP Benchmark

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Assessment Title

Rule Text

The Red Hat Enterprise Linux operating system must be configured so that the SSH daemon is configured to only use the SSHv2 protocol.

Description

Discussion Text

SSHv1 is an insecure implementation of the SSH protocol and has many well-known vulnerability exploits. Exploits of the SSH daemon could provide immediate root access to the system. Satisfies: SRG-OS-000074-GPOS-00042, SRG-OS-000480-GPOS-00227

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

IA Controls

NIST SP 800-53

Not mappedCCI-000197Not mappedCCI-000366SV-86875V-72251

References

DPMS Target Red Hat Enterprise Linux 7 DISA DPMS Target Red Hat Enterprise Linux 7 2899

Checks

DISA STIG (Manual Reference)

Check the version of the operating system with the following command:

# cat /etc/redhat-release

If the release is 7.4 or newer this requirement is Not Applicable.

Verify the SSH daemon is configured to only use the SSHv2 protocol.

Check that the SSH daemon is configured to only use the SSHv2 protocol with the following command:

# grep -i protocol /etc/ssh/sshd_config
Protocol 2
#Protocol 1,2

If any protocol line other than "Protocol 2" is uncommented, this is a finding.

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.rhel7:def:1373
# The Red Hat Enterprise Linux operating system must be configured so that the SSH daemon is configured to only use the SSHv2 protocol.
# Per-module read mechanism curated from static teardown of DISA's SCC tool
# (SCAP Compliance Checker) -- see the SCC Automation Reference above.

# package openssh-server is removed
# rpminfo_object (rpminfo_test)
test_1() {
  ! ( rpm -q --quiet 'openssh-server' &>/dev/null )
}
# Check Protocol in /etc/ssh/sshd_config
# textfilecontent54_object (textfilecontent54_test)
test_2() {
  (sed -En 's/^\s*Protocol[ \t]+([^\s#]*)[ \t]*(?:#.*)?$/\1/p' '/etc/ssh/sshd_config') | grep -Pq '^(2|"2")$'
}
# package openssh-server is version 7.4 or higher
# rpminfo_object (rpminfo_test)
test_3() {
  (rpm -q --qf '%|EPOCH?{%{EPOCH}}:{0}|:%{VERSION}-%{RELEASE}' 'openssh-server') | grep -qxF '0:7.4p1-0'
}

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
# This script implements the OVAL definition: oval:mil.disa.stig.rhel7:def:1373

if ! rpm -q openssh-server >/dev/null 2>&1; then
  echo "FAIL"
  exit 1
fi

if ! grep -q "^\\s*Protocol[ \\t]+2[ \\t]*(?:#.*)?$" /etc/ssh/sshd_config; then
  if ! sed -i '/^Protocol[ \\t]*1/d' /etc/ssh/sshd_config && echo "Protocol 2" >> /etc/ssh/sshd_config; then
    echo "FAIL"
    exit 1
  fi
fi

systemctl restart sshd

echo "PASS"
exit 0

Remediation

Remove all Protocol lines that reference version "1" in "/etc/ssh/sshd_config" (this file may be named differently or be in a different location if using a version of SSH that is provided by a third-party vendor). The "Protocol" line must be as follows:

Protocol 2

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