Cis Ubuntu1204 V110 9 3 12

---
name: cis-ubuntu1204-v110-9-3-12
description: "Set Idle Timeout Interval for User Login"
category: cis-os-hardening
version: "1.1.0"
author: cyberstrike-official
tags: [cis, ubuntu, 12.04, linux, authentication, ssh, timeout, idle]
cis_id: "9.3.12"
cis_benchmark: "CIS Ubuntu 12.04 LTS Server Benchmark v1.1.0"
tech_stack: [ubuntu, linux]
cwe_ids: []
chains_with: []
prerequisites: []
severity_boost: {}
---

# 9.3.12 Set Idle Timeout Interval for User Login (Scored)

## Profile Applicability

- Level 1

## Description

The two options `ClientAliveInterval` and `ClientAliveCountMax` control the timeout of ssh sessions. When the `ClientAliveInterval` variable is set, ssh sessions that have no activity for the specified length of time are terminated. When the `ClientAliveCountMax` variable is set, `sshd` will send client alive messages at every `ClientAliveInterval` interval. When the number of consecutive client alive messages are sent with no response from the client, the `ssh` session is terminated. For example, if the `ClientAliveInterval` is set to 15 seconds and the `ClientAliveCountMax` is set to 3, the client `ssh` session will be terminated after 45 seconds of idle time.

## Rationale

Having no timeout value associated with a connection could allow an unauthorized user access to another user's `ssh` session (e.g. user walks away from their computer and doesn't lock the screen). Setting a timeout value at least reduces the risk of this happening.

While the recommended setting is 300 seconds (5 minutes), set this timeout value based on site policy. The recommended setting for `ClientAliveCountMax` is 0. In this case, the client session will be terminated after 5 minutes of idle time and no keepalive messages will be sent.

## Audit Procedure

### Using Command Line

To verify the correct SSH setting, run the following command and verify that the output is as shown:

```bash
grep "^ClientAliveInterval" /etc/ssh/sshd_config
grep "^ClientAliveCountMax" /etc/ssh/sshd_config
```

## Expected Result

```
ClientAliveInterval 300
ClientAliveCountMax 0
```

## Remediation

### Using Command Line

Edit the `/etc/ssh/sshd_config` file to set the parameter as follows:

```bash
ClientAliveInterval 300
ClientAliveCountMax 0
```

## Default Value

ClientAliveInterval 0, ClientAliveCountMax 3

## References

- CIS Ubuntu 12.04 LTS Server Benchmark v1.1.0

## Profile

Level 1 - Scored