SV-248868r1261710: OL 8 must force a frequent session key renegotiation for SSH connections to the server. | Oracle Linux 8 STIG SCAP Benchmark

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Assessment Title

Rule Text

OL 8 must force a frequent session key renegotiation for SSH connections to the server.

Description

Discussion Text

Unapproved mechanisms that are used for authentication to the cryptographic module are not verified and therefore cannot be relied on to provide confidentiality or integrity, and DoW data may be compromised. Session key regeneration limits the chances of a session key becoming compromised.

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

IA Controls

NIST SP 800-53

Not mappedCCI-000068

References

DPMS Target Oracle Linux 8 DISA DPMS Target Oracle Linux 8 5416

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.ol8os:def:248868
# OL 8 must force a frequent session key renegotiation for SSH connections to the server.
# 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:RekeyLimit maximum data and time are greater than zero.
# textfilecontent54_object (textfilecontent54_test)
test_1() {
  (grep -oP '^\s*RekeyLimit\s+\d+[kmg]?\s+\d+[smdhw]?\s*' '/etc/ssh/sshd_config') | grep -Pq '^(?i)\s*RekeyLimit\s+[1-9][0-9]*[kmg]?\s+([1-9][0-9]*[smhdw]?)+\s*$'
}
# sshd_config includes sshd_config.d
# textfilecontent54_object (textfilecontent54_test)
test_2() {
  (sed -En 's/^\s*include\s+(.*)\s*$/\1/p' '/etc/ssh/sshd_config') | grep -qxF '/etc/ssh/sshd_config.d/*.conf'
}
# /etc/ssh/sshd_config.d:RekeyLimit maximum data and time are greater than zero.
# textfilecontent54_object (textfilecontent54_test)
test_3() {
  (grep -rhoP --include='*.conf' '^\s*RekeyLimit\s+\d+[kmg]?\s+\d+[smdhw]?\s*' '/etc/ssh/sshd_config.d') | grep -Pq '^(?i)\s*RekeyLimit\s+[1-9][0-9]*[kmg]?\s+([1-9][0-9]*[smhdw]?)+\s*$'
}

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.ol8os:def:248868

if [ ! -f "/etc/ssh/sshd_config" ]; then
  echo "PASS"
  exit 0
fi

grep -qE "^\\s*RekeyLimit\\s+[1-9][0-9]*[kmg]?\\s+([1-9][0-9]*[smhdw]?)+\\s*$" /etc/ssh/sshd_config || {
  echo "FAIL"
  exit 1
}

if [ $(grep -c "^\\s*include\\s+.*\\.conf\\s*$" /etc/ssh/sshd_config) -ge 1 ]; then
  grep -r -l -E "^\\s*RekeyLimit\\s+[1-9][0-9]*[kmg]?\\s+([1-9][0-9]*[smhdw]?)+\\s*$" /etc/ssh/sshd_config.d || {
    echo "FAIL"
    exit 1
  }
fi

echo "PASS"
exit 0

Remediation

Configure the system to force a frequent session key renegotiation for SSH connections to the server by adding or modifying the following line in the "/etc/ssh/sshd_config" file: 
 
RekeyLimit 1G 1h 
 
The SSH daemon must be restarted for the settings to take effect. 
 
$ sudo systemctl restart sshd.service