SV-270667r1261512: Ubuntu 24.04 LTS must configure the SSH daemon to use FIPS 140-3 approved ciphers to prevent the unauthorized disclosure of information and/or detect changes to information during transmission. | Canonical Ubuntu 24.04 LTS STIG SCAP Benchmark

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Assessment Title

Rule Text

Ubuntu 24.04 LTS must configure the SSH daemon to use FIPS 140-3 approved ciphers to prevent the unauthorized disclosure of information and/or detect changes to information during transmission.

Description

Discussion Text

Without cryptographic integrity protections, information can be altered by unauthorized users without detection. Remote access (e.g., RDP) is access to DoW nonpublic information systems by an authorized user (or an information system) communicating through an external, nonorganization-controlled network. Remote access methods include, for example, dial-up, broadband, and wireless. Nonlocal maintenance and diagnostic activities are those activities conducted by individuals communicating through a network, either an external network (e.g., the internet) or an internal network. Local maintenance and diagnostic activities are those activities carried out by individuals physically present at the information system or information system component and not communicating across a network connection. Encrypting information for transmission protects information from unauthorized disclosure and modification. Cryptographic mechanisms implemented to protect information integrity include, for example, cryptographic hash functions that have common application in digital signatures, checksums, and message authentication codes. Satisfies: SRG-OS-000033-GPOS-00014, SRG-OS-000394-GPOS-00174, SRG-OS-000424-GPOS-00188

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

IA Controls

NIST SP 800-53

Not mappedCCI-000068Not mappedCCI-003123Not mappedCCI-002421

References

DPMS Target Canonical Ubuntu 24.04 LTS DISA DPMS Target Canonical Ubuntu 24.04 LTS 5673

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.ubuntu2404os:def:270667
# Ubuntu 24.04 LTS must configure the SSH daemon to use FIPS 140-3 approved ciphers to prevent the unauthorized disclosure of information and/or detect changes to information during transmission.
# 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:Ciphers == DoW-approved ciphers
# textfilecontent54_object (textfilecontent54_test)
test_1() {
  ( (sed -En 's/^\s*(?i)Ciphers(?-i)[ \t]+\"?([\w,-@]+)\"?[\s]*(?:|(?:#.*))?$/\1/p' '/etc/ssh/sshd_config') | grep -Pq '^(?:(aes256-gcm@openssh.com,aes128-gcm@openssh.com,aes256-ctr,aes128-ctr)|(aes256-gcm@openssh.com,aes128-gcm@openssh.com,aes128-ctr,aes256-ctr)|(aes256-gcm@openssh.com,aes128-ctr,aes128-gcm@openssh.com,aes256-ctr)|(aes256-gcm@openssh.com,aes128-ctr,aes256-ctr,aes128-gcm@openssh.com)|(aes256-gcm@openssh.com,aes256-ctr,aes128-gcm@openssh.com,aes128-ctr)|(aes256-gcm@openssh.com,aes256-ctr,aes128-ctr,aes128-gcm@openssh.com)|(aes128-gcm@openssh.com,aes256-gcm@openssh.com,aes256-ctr,aes128-ctr)|(aes128-gcm@openssh.com,aes256-gcm@openssh.com,aes128-ctr,aes256-ctr)|(aes128-gcm@openssh.com,aes128-ctr,aes256-gcm@openssh.com,aes256-ctr)|(aes128-gcm@openssh.com,aes128-ctr,aes256-ctr,aes256-gcm@openssh.com)|(aes128-gcm@openssh.com,aes256-ctr,aes256-gcm@openssh.com,aes128-ctr)|(aes128-gcm@openssh.com,aes256-ctr,aes128-ctr,aes256-gcm@openssh.com)|(aes256-ctr,aes256-gcm@openssh.com,aes128-gcm@openssh.com,aes128-ctr)|(aes256-ctr,aes256-gcm@openssh.com,aes128-ctr,aes128-gcm@openssh.com)|(aes256-ctr,aes128-ctr,aes256-gcm@openssh.com,aes128-gcm@openssh.com)|(aes256-ctr,aes128-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com)|(aes256-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com,aes128-ctr)|(aes256-ctr,aes128-gcm@openssh.com,aes128-ctr,aes256-gcm@openssh.com)|(aes128-ctr,aes256-gcm@openssh.com,aes128-gcm@openssh.com,aes256-ctr)|(aes128-ctr,aes256-gcm@openssh.com,aes256-ctr,aes128-gcm@openssh.com)|(aes128-ctr,aes256-ctr,aes256-gcm@openssh.com,aes128-gcm@openssh.com)|(aes128-ctr,aes256-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com)|(aes128-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com,aes256-ctr)|(aes128-ctr,aes128-gcm@openssh.com,aes256-ctr,aes256-gcm@openssh.com))$' ) || ( (grep -rhP --include='*.conf' '^\s*(?i)Ciphers(?-i)[ \t]+\"?([\w,-@]+)\"?[\s]*(?:|(?:#.*))?$' '/etc/ssh/sshd_config.d' | sed -En 's/^\s*(?i)Ciphers(?-i)[ \t]+\"?([\w,-@]+)\"?[\s]*(?:|(?:#.*))?$/\1/p') | grep -Pq '^(?:(aes256-gcm@openssh.com,aes128-gcm@openssh.com,aes256-ctr,aes128-ctr)|(aes256-gcm@openssh.com,aes128-gcm@openssh.com,aes128-ctr,aes256-ctr)|(aes256-gcm@openssh.com,aes128-ctr,aes128-gcm@openssh.com,aes256-ctr)|(aes256-gcm@openssh.com,aes128-ctr,aes256-ctr,aes128-gcm@openssh.com)|(aes256-gcm@openssh.com,aes256-ctr,aes128-gcm@openssh.com,aes128-ctr)|(aes256-gcm@openssh.com,aes256-ctr,aes128-ctr,aes128-gcm@openssh.com)|(aes128-gcm@openssh.com,aes256-gcm@openssh.com,aes256-ctr,aes128-ctr)|(aes128-gcm@openssh.com,aes256-gcm@openssh.com,aes128-ctr,aes256-ctr)|(aes128-gcm@openssh.com,aes128-ctr,aes256-gcm@openssh.com,aes256-ctr)|(aes128-gcm@openssh.com,aes128-ctr,aes256-ctr,aes256-gcm@openssh.com)|(aes128-gcm@openssh.com,aes256-ctr,aes256-gcm@openssh.com,aes128-ctr)|(aes128-gcm@openssh.com,aes256-ctr,aes128-ctr,aes256-gcm@openssh.com)|(aes256-ctr,aes256-gcm@openssh.com,aes128-gcm@openssh.com,aes128-ctr)|(aes256-ctr,aes256-gcm@openssh.com,aes128-ctr,aes128-gcm@openssh.com)|(aes256-ctr,aes128-ctr,aes256-gcm@openssh.com,aes128-gcm@openssh.com)|(aes256-ctr,aes128-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com)|(aes256-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com,aes128-ctr)|(aes256-ctr,aes128-gcm@openssh.com,aes128-ctr,aes256-gcm@openssh.com)|(aes128-ctr,aes256-gcm@openssh.com,aes128-gcm@openssh.com,aes256-ctr)|(aes128-ctr,aes256-gcm@openssh.com,aes256-ctr,aes128-gcm@openssh.com)|(aes128-ctr,aes256-ctr,aes256-gcm@openssh.com,aes128-gcm@openssh.com)|(aes128-ctr,aes256-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com)|(aes128-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com,aes256-ctr)|(aes128-ctr,aes128-gcm@openssh.com,aes256-ctr,aes256-gcm@openssh.com))$' )
}

if test_1; then
  echo "PASS"
else
  echo "FAIL"
fi

Remediation

Configure Ubuntu 24.04 LTS to allow the SSH daemon to only implement FIPS-approved 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-gcm@openssh.com,aes128-gcm@openssh.com,aes256-ctr,aes128-ctr
 
Restart the "sshd" service for changes to take effect: 
 
$ sudo systemctl restart sshd