SV-204578r958408: The Red Hat Enterprise Linux 7 operating system must implement DoD-approved encryption to protect the confidentiality of SSH connections. | Red Hat Enterprise Linux 7 STIG SCAP Benchmark

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Assessment Title

Rule Text

The Red Hat Enterprise Linux 7 operating system must implement DoD-approved encryption to protect the confidentiality of SSH connections.

Description

Discussion Text

Unapproved mechanisms that are used for authentication to the cryptographic module are not verified and therefore cannot be relied upon to provide confidentiality or integrity, and DoD data may be compromised. Operating systems utilizing encryption are required to use FIPS-compliant mechanisms for authenticating to cryptographic modules. FIPS 140-2 is the current standard for validating that mechanisms used to access cryptographic modules utilize authentication that meets DoD requirements. This allows for Security Levels 1, 2, 3, or 4 for use on a general purpose computing system. The system will attempt to use the first cipher presented by the client that matches the server list. Listing the values "strongest to weakest" is a method to ensure the use of the strongest cipher available to secure the SSH connection. Satisfies: SRG-OS-000033-GPOS-00014, SRG-OS-000120-GPOS-00061, SRG-OS-000125-GPOS-00065, SRG-OS-000250-GPOS-00093, SRG-OS-000393-GPOS-00173

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

IA Controls

NIST SP 800-53

Not mappedCCI-000068Not mappedCCI-000366Not mappedCCI-000803V-72221SV-86845

References

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

Checks

DISA STIG (Manual Reference)

Verify the operating system uses mechanisms meeting the requirements of applicable federal laws, Executive orders, directives, policies, regulations, standards, and guidance for authentication to a cryptographic module.

The location of the "sshd_config" file may vary if a different daemon is in use.

Inspect the "Ciphers" configuration with the following command:

# grep -i ciphers /etc/ssh/sshd_config
Ciphers aes256-ctr,aes192-ctr,aes128-ctr

If any ciphers other than "aes256-ctr", "aes192-ctr", or "aes128-ctr" are listed, the order differs from the example above, the "Ciphers" keyword is missing, or the returned line is commented out, 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:1399
# The Red Hat Enterprise Linux 7 operating system must implement DoD-approved encryption to protect the confidentiality of SSH connections.
# 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 the Cipers list in /etc/ssh/sshd_config
# textfilecontent54_object (textfilecontent54_test)
test_2() {
  (sed -En 's/^[\s]*Ciphers[\s]+(.*)/\1/p' '/etc/ssh/sshd_config') | grep -Pq '^"?(aes256-ctr,aes192-ctr,aes128-ctr)"?[\s]*(?:|(?:#.*))?$'
}

if ( test_1 || test_2 ); 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.rhel7:def:1399

if ! rpm -q openssh-server &> /dev/null; then
  echo "PASS"
  exit 0
fi

if grep -q '^[[:space:]]*Ciphers[[:space:]]*aes256-ctr,aes192-ctr,aes128-ctr' /etc/ssh/sshd_config; then
  echo "PASS"
  exit 0
fi

echo "FAIL"
exit 1

Remediation

Configure SSH to use FIPS 140-2 approved cryptographic algorithms.

Add the following line (or modify the line to have the required value) to the "/etc/ssh/sshd_config" file (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).

Ciphers aes256-ctr,aes192-ctr,aes128-ctr

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