SV-274051r1120141: Amazon Linux 2023 must be configured so that all network connections associated with SSH traffic terminate after becoming unresponsive. | Amazon Linux 2023 STIG SCAP Benchmark

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Assessment Title

Rule Text

Amazon Linux 2023 must be configured so that all network connections associated with SSH traffic terminate after becoming unresponsive.

Description

Discussion Text

Terminating an idle session within a short time period reduces the window of opportunity for unauthorized personnel to take control of a management session enabled on the console or console port that has been left unattended. In addition, quickly terminating an idle session will also free up resources committed by the managed network element. Terminating network connections associated with communications sessions includes, for example, de-allocating associated TCP/IP address/port pairs at Amazon Linux 2023 level, and de-allocating networking assignments at the application level if multiple application sessions are using a single operating system-level network connection. This does not mean that Amazon Linux 2023 terminates all sessions or network access; it only ends the inactive session and releases the resources associated with that session. Satisfies: SRG-OS-000163-GPOS-00072, SRG-OS-000279-GPOS-00109

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

IA Controls

NIST SP 800-53

Not mappedCCI-001133Not mappedCCI-002361

References

DPMS Target Amazon Linux 2023 DISA DPMS Target Amazon Linux 2023 5700

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.amzlx23os:def:274051
# Amazon Linux 2023 must be configured so that all network connections associated with SSH traffic terminate after becoming unresponsive.
# 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:ClientAliveCountMax = 1
# textfilecontent54_object (textfilecontent54_test)
test_1() {
  ( [ "$(sed -En 's/^\s*(?i)ClientAliveCountMax(?-i)\s+"?(\d+)"?\s*(?:|(?:#.*))?$/\1/p' '/etc/ssh/sshd_config')" -eq 1 ] ) || ( [ "$(grep -rhP --include='*' '^\s*(?i)ClientAliveCountMax(?-i)\s+"?(\d+)"?\s*(?:|(?:#.*))?$' '/etc/ssh/sshd_config.d' | sed -En 's/^\s*(?i)ClientAliveCountMax(?-i)\s+"?(\d+)"?\s*(?:|(?:#.*))?$/\1/p')" -eq 1 ] )
}

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
# This script implements the OVAL definition: oval:mil.disa.stig.amzlx23os:def:274051

FILEPATH1="/etc/ssh/sshd_config"
FILEPATH2="/etc/ssh/sshd_config.d/*.conf"

if [ ! -f "$FILEPATH1" ] && [ ! -d "$FILEPATH2" ]; then
  echo "PASS"
  exit 0
fi

if [ -f "$FILEPATH1" ]; then
  grep -qE "^\\s*(?i)ClientAliveCountMax(?-i)\\s+\"?(\\d+)\"?\\s*" "$FILEPATH1" && \
  grep -Po '(?<=ClientAliveCountMax\\s+)\\d+' "$FILEPATH1" | grep -qE "^1$" || \
  echo "FAIL"
  exit 1
fi

for file in $FILEPATH2; do
  if [ -f "$file" ]; then
    grep -qE "^\\s*(?i)ClientAliveCountMax(?-i)\\s+\"?(\\d+)\"?\\s*" "$file" && \
    grep -Po '(?<=ClientAliveCountMax\\s+)\\d+' "$file" | grep -qE "^1$" || \
    echo "FAIL"
    exit 1
  fi
done

echo "PASS"
exit 0

Remediation

Configure Amazon Linux 2023 SSHD to terminate a user session automatically after the SSH client has become unresponsive.

Note: This setting must be applied in conjunction with AZLX-23-000820 to function correctly.

Modify or append the following lines in the "/etc/ssh/sshd_config" file or a dropfile in "/etc/ssh/sshd_config.d":

ClientAliveCountMax 1

For the changes to take effect, the SSH daemon must be restarted.

$ sudo systemctl restart sshd.service