SV-260531r1261454: Ubuntu 22.04 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 22.04 LTS STIG SCAP Benchmark

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Assessment Title

Rule Text

Ubuntu 22.04 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 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, which have common application in digital signatures, checksums, and message authentication codes. By specifying a cipher list with the order of ciphers being in a "strongest to weakest" orientation, the system will automatically attempt to use the strongest cipher for securing SSH connections. 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-002421Not mappedCCI-003123

References

DPMS Target Canonical Ubuntu 22.04 LTS DISA DPMS Target Canonical Ubuntu 22.04 LTS 5594

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.ubuntu2204os:def:260531
# Ubuntu 22.04 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]*(?:|(?:#.*))?$/\1/p' '/etc/ssh/sshd_config') | grep -Pq '^(?:(aes256-gcm@openssh.com,aes128-gcm@openssh.com,aes256-ctr,aes128-ctr)|(aes256-gcm@openssh.com,aes128-gcm@openssh.com,aes128-ctr,aes256-ctr)|(aes256-gcm@openssh.com,aes128-ctr,aes128-gcm@openssh.com,aes256-ctr)|(aes256-gcm@openssh.com,aes128-ctr,aes256-ctr,aes128-gcm@openssh.com)|(aes256-gcm@openssh.com,aes256-ctr,aes128-gcm@openssh.com,aes128-ctr)|(aes256-gcm@openssh.com,aes256-ctr,aes128-ctr,aes128-gcm@openssh.com)|(aes128-gcm@openssh.com,aes256-gcm@openssh.com,aes256-ctr,aes128-ctr)|(aes128-gcm@openssh.com,aes256-gcm@openssh.com,aes128-ctr,aes256-ctr)|(aes128-gcm@openssh.com,aes128-ctr,aes256-gcm@openssh.com,aes256-ctr)|(aes128-gcm@openssh.com,aes128-ctr,aes256-ctr,aes256-gcm@openssh.com)|(aes128-gcm@openssh.com,aes256-ctr,aes256-gcm@openssh.com,aes128-ctr)|(aes128-gcm@openssh.com,aes256-ctr,aes128-ctr,aes256-gcm@openssh.com)|(aes256-ctr,aes256-gcm@openssh.com,aes128-gcm@openssh.com,aes128-ctr)|(aes256-ctr,aes256-gcm@openssh.com,aes128-ctr,aes128-gcm@openssh.com)|(aes256-ctr,aes128-ctr,aes256-gcm@openssh.com,aes128-gcm@openssh.com)|(aes256-ctr,aes128-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com)|(aes256-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com,aes128-ctr)|(aes256-ctr,aes128-gcm@openssh.com,aes128-ctr,aes256-gcm@openssh.com)|(aes128-ctr,aes256-gcm@openssh.com,aes128-gcm@openssh.com,aes256-ctr)|(aes128-ctr,aes256-gcm@openssh.com,aes256-ctr,aes128-gcm@openssh.com)|(aes128-ctr,aes256-ctr,aes256-gcm@openssh.com,aes128-gcm@openssh.com)|(aes128-ctr,aes256-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com)|(aes128-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com,aes256-ctr)|(aes128-ctr,aes128-gcm@openssh.com,aes256-ctr,aes256-gcm@openssh.com))$'
}

if test_1; 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:mil.disa.stig.ubuntu2204os:def:260531
if [ ! -f "/etc/ssh/sshd_config" ]; then echo "PASS"; exit 0; fi
grep -q "^Ciphers aes256-gcm@openssh.com,aes128-gcm@openssh.com,aes256-ctr,aes128-ctr" /etc/ssh/sshd_config || grep -q "^Ciphers aes256-gcm@openssh.com,aes128-gcm@openssh.com,aes128-ctr,aes256-ctr" /etc/ssh/sshd_config || grep -q "^Ciphers aes256-gcm@openssh.com,aes128-ctr,aes128-gcm@openssh.com,aes256-ctr" /etc/ssh/sshd_config || grep -q "^Ciphers aes256-gcm@openssh.com,aes128-ctr,aes256-ctr,aes128-gcm@openssh.com" /etc/ssh/sshd_config || grep -q "^Ciphers aes256-gcm@openssh.com,aes256-ctr,aes128-gcm@openssh.com,aes128-ctr" /etc/ssh/sshd_config || grep -q "^Ciphers aes256-gcm@openssh.com,aes256-ctr,aes128-ctr,aes128-gcm@openssh.com" /etc/ssh/sshd_config || grep -q "^Ciphers aes128-gcm@openssh.com,aes256-gcm@openssh.com,aes256-ctr,aes128-ctr" /etc/ssh/sshd_config || grep -q "^Ciphers aes128-gcm@openssh.com,aes256-gcm@openssh.com,aes128-ctr,aes256-ctr" /etc/ssh/sshd_config || grep -q "^Ciphers aes128-gcm@openssh.com,aes128-ctr,aes256-gcm@openssh.com,aes256-ctr" /etc/ssh/sshd_config || grep -q "^Ciphers aes128-gcm@openssh.com,aes128-ctr,aes256-ctr,aes256-gcm@openssh.com" /etc/ssh/sshd_config || grep -q "^Ciphers aes128-gcm@openssh.com,aes256-ctr,aes256-gcm@openssh.com,aes128-ctr" /etc/ssh/sshd_config || grep -q "^Ciphers aes128-gcm@openssh.com,aes256-ctr,aes128-ctr,aes256-gcm@openssh.com" /etc/ssh/sshd_config || grep -q "^Ciphers aes256-ctr,aes256-gcm@openssh.com,aes128-gcm@openssh.com,aes128-ctr" /etc/ssh/sshd_config || grep -q "^Ciphers aes256-ctr,aes256-gcm@openssh.com,aes128-ctr,aes128-gcm@openssh.com" /etc/ssh/sshd_config || grep -q "^Ciphers aes256-ctr,aes128-ctr,aes256-gcm@openssh.com,aes128-gcm@openssh.com" /etc/ssh/sshd_config || grep -q "^Ciphers aes256-ctr,aes128-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com" /etc/ssh/sshd_config || grep -q "^Ciphers aes256-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com,aes128-ctr" /etc/ssh/sshd_config || grep -q "^Ciphers aes256-ctr,aes128-gcm@openssh.com,aes128-ctr,aes256-gcm@openssh.com" /etc/ssh/sshd_config || grep -q "^Ciphers aes128-ctr,aes256-gcm@openssh.com,aes128-gcm@openssh.com,aes256-ctr" /etc/ssh/sshd_config || grep -q "^Ciphers aes128-ctr,aes256-gcm@openssh.com,aes256-ctr,aes128-gcm@openssh.com" /etc/ssh/sshd_config || grep -q "^Ciphers aes128-ctr,aes256-ctr,aes256-gcm@openssh.com,aes128-gcm@openssh.com" /etc/ssh/sshd_config || grep -q "^Ciphers aes128-ctr,aes256-ctr,aes128-gcm@openssh.com,aes256-gcm@openssh.com" /etc/ssh/sshd_config; if [ $? -eq 0 ]; then echo "PASS"; exit 0; else echo "FAIL"; exit 1; fi

Remediation

Configure the SSH server to only implement FIPS-approved ciphers.  

Add or modify the following line in the "/etc/ssh/sshd_config" file: 

Ciphers aes256-ctr,aes256-gcm@openssh.com,aes128-ctr,aes128-gcm@openssh.com 

Restart SSH for the changes to take effect: 

$ sudo systemctl restart ssh