Ensure sshd ClientAliveInterval and ClientAliveCountMax are configured

MediumLevel 1Automatedaix

Description

Note: To clarify, the two settings described below are only meant for idle connections from a protocol perspective and are not meant to check if the user is active or not. An idle user does not mean an idle connection. SSH does not and never had, intentionally, the capability to drop idle users. In order to prevent resource exhaustion, appropriate values should be set for both ClientAliveInterval and ClientAliveCountMax. Audit: evaluates the effective configuration from `sshd -T` (Match blocks must be reviewed separately).

How it is checked

Audit method: Shell command

shell

command -v sshd >/dev/null 2>&1 || exit 1; out=$(sshd -T 2>/dev/null) || exit 1; r=compliant; for p in '^clientaliveinterval[[:blank:]]+[1-9][0-9]*$' '^clientalivecountmax[[:blank:]]+[1-9][0-9]*$'; do printf '%s\n' "$out" | grep -Eiq -- "$p" || r="not matched: $p"; done; echo "$r"

Expected output: compliant

How it is fixed

Fix method: Guidance or infrastructure patch

Edit the /etc/ssh/sshd_config file to set the ClientAliveInterval and ClientAliveCountMax parameters above any Include and Match entries according to site policy. Example: ClientAliveInterval 15 ClientAliveCountMax 3 Note: First occurrence of a option takes precedence, Match set statements withstanding. If Include locations are enabled, used, and order of precedence is understood in your environment, the entry may be created in a file in Include location.

Properties

Operating systems: Any
Tags: aixssh
Reference: CIS IBM AIX 7 Benchmark v1.2.0 - 4.6.3.18 Ensure sshd ClientAliveInterval and ClientAliveCountMax are configured

Check this host

Run this on a machine you are allowed to audit. The scan is read-only.

shell

tmaegis scan --target aix