Cis Ubuntu2004 V300 5 1 16

---
name: cis-ubuntu2004-v300-5-1-16
description: "Ensure sshd MaxAuthTries is configured"
category: cis-networking
version: "3.0.0"
author: cyberstrike-official
tags: [cis, ubuntu, linux, ubuntu-20.04, ssh]
cis_id: "5.1.16"
cis_benchmark: "CIS Ubuntu Linux 20.04 LTS Benchmark v3.0.0"
tech_stack: [ubuntu, linux]
cwe_ids: []
chains_with: []
prerequisites: []
severity_boost: {}
---

# Ensure sshd MaxAuthTries is configured (Automated)

## Profile Applicability

- Level 1 - Server
- Level 1 - Workstation

## Description

The `MaxAuthTries` parameter specifies the maximum number of authentication attempts permitted per connection. When the login failure count reaches half the number, error messages will be written to the `syslog` file detailing the login failure.

## Rationale

Setting the `MaxAuthTries` parameter to a low number will minimize the risk of successful brute force attacks to the SSH server. While the recommended setting is 4, set the number based on site policy.

## Audit Procedure

### Command Line

Run the following command and verify that `MaxAuthTries` is `4` or less:

```bash
# sshd -T | grep maxauthtries
```

```
maxauthtries 4
```

- IF - `Match` set statements are used in your environment, specify the connection parameters to use for the `-T` extended test mode and run the audit to verify the setting is not incorrectly configured in a match block.
  Example additional audit needed for a match block for the user _sshuser_:

```bash
# sshd -T -C user=sshuser | grep maxauthtries
```

Note: If provided, any Match directives in the configuration file that would apply are applied before the configuration is written to standard output. The connection parameters are supplied as keyword=value pairs and may be supplied in any order, either with multiple `-C` options or as a comma-separated list. The keywords are `addr` (source address), `user` (user), `host` (resolved source host name), `laddr` (local address), `lport` (local port number), and `rdomain` (routing domain).

## Expected Result

```
maxauthtries 4
```

(or a value of 4 or less)

## Remediation

### Command Line

Edit the `/etc/ssh/sshd_config` file to set the `MaxAuthTries` parameter to `4` or less above any `Include` and `Match` entries as follows:

```
MaxAuthTries 4
```

Note: First occurrence of an 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.

## Default Value

MaxAuthTries 6

## References

1. SSHD_CONFIG(5)
2. NIST SP 800-53 Rev. 5: AU-3

## CIS Controls

v8 - 8.5 Collect Detailed Audit Logs
Configure detailed audit logging for enterprise assets containing sensitive data. Include event source, date, username, timestamp, source addresses, destination addresses, and other useful elements that could assist in a forensic investigation.

v7 - 16.13 Alert on Account Login Behavior Deviation
Alert when users deviate from normal login behavior, such as time-of-day, workstation location and duration.

MITRE ATT&CK Mappings: T1110, T1110.001, T1110.003 | TA0006 | M1036