cyberstrikeus 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:
# sshd -T | grep maxauthtries
maxauthtries 4
- IF -
Matchset statements are used in your environment, specify the connection parameters to use for the-Textended 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:
# 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
- SSHD_CONFIG(5)
- 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