SV-215129r610931: The Ubuntu operating system must be configured so that all network connections associated with SSH traffic are terminated at the end of the session or after 10 minutes of inactivity, except to fulfill documented and validated mission requirements. | Canonical Ubuntu 16.04 LTS Security Technical Implementation Guide

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Assessment Title

Rule Text

The Ubuntu operating system must be configured so that all network connections associated with SSH traffic are terminated at the end of the session or after 10 minutes of inactivity, except to fulfill documented and validated mission requirements.

Description

Discussion Text

Automatic session termination addresses the termination of user-initiated logical sessions in contrast to the termination of network connections that are associated with communications sessions (i.e., network disconnect). A logical session (for local, network, and remote access) is initiated whenever a user (or process acting on behalf of a user) accesses an organizational information system. Such user sessions can be terminated (and thus terminate user access) without terminating network sessions. Session termination terminates all processes associated with a user's logical session except those processes that are specifically created by the user (i.e., session owner) to continue after the session is terminated. Conditions or trigger events requiring automatic session termination can include, for example, organization-defined periods of user inactivity, targeted responses to certain types of incidents, and time-of-day restrictions on information system use. This capability is typically reserved for specific Ubuntu operating system functionality where the system owner, data owner, or organization requires additional assurance.

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

IA Controls

NIST SP 800-53

Not mappedCCI-002361Not mappedCCI-000879Not mappedCCI-001133SV-90517V-75837

References

DPMS Target Canonical Ubuntu 16.04 LTS DISA DPMS Target Canonical Ubuntu 16.04 LTS 4011

Checks

DISA STIG (Manual Reference)

Verify that all network connections associated with SSH traffic are automatically terminated at the end of the session or after "10" minutes of inactivity.

Check that the "ClientAliveInterval" variable is set to a value of "600" or less by performing the following command:

# sudo grep -i clientalive /etc/ssh/sshd_config

ClientAliveInterval 600

If "ClientAliveInterval" has a value that is greater than "600" and is not documented with the Information System Security Officer (ISSO) as an operational requirement, or 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.ubuntu1604:def:236
# The Ubuntu operating system must be configured so that all network connections associated with SSH traffic are terminated at the end of the session or after 10 minutes of inactivity, except to fulfill documented and validated mission requirements.
# Per-module read mechanism curated from static teardown of DISA's SCC tool
# (SCAP Compliance Checker) -- see the SCC Automation Reference above.

# The openssh-server package is installed
# dpkginfo_object (dpkginfo_test)
test_1() {
  grep -A1 '^Package: openssh-server$' /var/lib/dpkg/status &>/dev/null
}
# /etc/ssh/sshd_config:ClientAliveInterval == 600
# textfilecontent54_object (textfilecontent54_test)
test_2() {
  [ "$(sed -En 's/^\s*(?i)ClientAliveInterval(?-i)[ \t]+"?(\d+)"?\s*(?:|(?:#.*))?$/\1/p' '/etc/ssh/sshd_config')" -le 600 ]
}

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:mil.disa.stig.ubuntu1604:def:236

if ! command -v dpkg &> /dev/null || ! dpkg -l | awk '/^ii/{print $2}' | grep -q "openssh-server"; then
    echo "PASS"
    exit 0
fi

if ! grep -qE '^\s*ClientAliveInterval\s+[0-9]+\s*$' /etc/ssh/sshd_config && ! [ $(grep -oE '^\s*ClientAliveInterval\s+[0-9]+\s*$' /etc/ssh/sshd_config | awk '{print $2}' | xargs) -le 600 ]; then
    echo "FAIL"
    exit 1
fi

echo "PASS"
exit 0

Remediation

Configure the Ubuntu operating system to automatically terminate all network connections associated with SSH traffic at the end of a session or after a "10" minute period of inactivity.

Modify or append the following lines in the "/etc/ssh/sshd_config" file replacing "[Interval]" with a value of "600" or less:

ClientAliveInterval 600

In order for the changes to take effect, the SSH daemon must be restarted.

# sudo systemctl restart sshd.service