Minimum password length

[アーティクル]
08/31/2016

Applies To: Windows Vista, Windows Server 2008, Windows 7, Windows 8.1, Windows Server 2008 R2, Windows Server 2012 R2, Windows Server 2012, Windows 8

This security policy reference topic for the IT professional describes the best practices, location, values, policy management, and security considerations for this policy setting.

Reference

The Minimum password length policy setting determines the least number of characters that can make up a password for a user account. You can set a value of between 1 and 14 characters, or you can establish that no password is required by setting the number of characters to 0.

This policy setting is supported on versions of Windows that are designated in the Applies To list at the beginning of this topic.

Possible values

User-specified number of characters between 0 and 14
Not defined

Best practices

Set Minimum password length value to 14. If the number of characters is set to 0, no password is required. In most environments, a fourteen-character password is recommended because it is long enough to provide adequate security and still short enough for users to easily remember. This value will help provide adequate defense against a brute force attack. Adding complexity requirements will help reduce the possibility of a dictionary attack. For more information, see Password must meet complexity requirements.

Permitting short passwords reduces security because short passwords can be easily broken with tools that perform dictionary or brute force attacks against the passwords. Requiring very long passwords can result in mistyped passwords that might cause an account lockout and subsequently increase the volume of Help Desk calls.

In addition, requiring extremely long passwords can actually decrease the security of an organization because users might be more likely to write down their passwords to avoid forgetting them. However, if users are taught that they can use passphrases (sentences such as "I want to drink a $5 milkshake"), they should be much more likely to remember.

Location

GPO_name**\Computer Configuration\Windows Settings\Security Settings\Account Policies\Password Policy**

Default values

The following table lists the actual and effective default policy values for the most recent supported versions of Windows. Default values are also listed on the policy’s property page.

Server type or Group Policy Object (GPO)	Default value
Default domain policy	7 characters
Default domain controller policy	Not defined
Stand-alone server default settings	0 characters
Domain controller effective default settings	7 characters
Member server effective default settings	7 characters
Effective GPO default settings on client computers	0 characters

Operating system version differences

There are no differences in the way this policy setting works between supported versions of Windows.

Policy management

This section describes features, tools, and guidance to help you manage this policy.

Restart requirement

None. Changes to this policy become effective without a computer restart when they are saved locally or distributed through Group Policy.

Security considerations

This section describes how an attacker might exploit a feature or its configuration, how to implement the countermeasure, and the possible negative consequences of countermeasure implementation.

Vulnerability

Types of password attacks include dictionary attacks (which attempt to use common words and phrases) and brute force attacks (which try every possible combination of characters). Also, attackers sometimes try to obtain the account database so they can use tools to discover the accounts and passwords.

Countermeasure

Configure the Minimum password length policy setting to a value of 8 or more. If the number of characters is set to 0, no password will be required.

In most environments, we recommend an eight-character password because it is long enough to provide adequate security, but not too difficult for users to easily remember. This configuration provides adequate defense against a brute force attack. Using the Passwords must meet complexity requirements policy setting in addition to the Minimum password length setting helps reduce the possibility of a dictionary attack.

Note

Some jurisdictions have established legal requirements for password length as part of establishing computer security regulations.

Potential impact

Requirements for extremely long passwords can actually decrease the security of an organization because users might leave the information in an unsecured location or lose it. If very long passwords are required, mistyped passwords could cause account lockouts and increase the volume of Help Desk calls. If your organization has issues with forgotten passwords due to password length requirements, consider teaching your users about passphrases, which are often easier to remember and, due to the larger number of character combinations, much harder to discover.