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1.1.5 Ensure 'Password must meet complexity requirements' is set to 'Enabled'

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Information

This policy setting checks all new passwords to ensure that they meet basic requirements for strong passwords.

When this policy is enabled, passwords must meet the following minimum requirements:
-- Not contain the user's account name or parts of the user's full name that exceed two consecutive characters

-- Be at least six characters in length

-- Contain characters from three of the following four categories:

---- English uppercase characters (A through Z)

---- English lowercase characters (a through z)

---- Base 10 digits (0 through 9)

---- Non-alphabetic characters (for example, !, $, #, %)

---- A catch-all category of any Unicode character that does not fall under the previous four categories. This fifth category can be regionally specific.

Each additional character in a password increases its complexity exponentially. For instance, a seven-character, all lower-case alphabetic password would have 267 (approximately 8 x 109 or 8 billion) possible combinations. At 1,000,000 attempts per second (a capability of many password-cracking utilities), it would only take 133 minutes to crack. A seven-character alphabetic password with case sensitivity has 527 combinations. A seven-character case-sensitive alphanumeric password without punctuation has 627 combinations. An eight-character password has 268 (or 2 x 1011) possible combinations. Although this might seem to be a large number, at 1,000,000 attempts per second it would take only 59 hours to try all possible passwords. Remember, these times will significantly increase for passwords that use ALT characters and other special keyboard characters such as '!' or '@'. Proper use of the password settings can help make it difficult to mount a brute force attack.

The recommended state for this setting is: 'Enabled'.

Rationale:
Passwords that contain only alphanumeric characters are extremely easy to discover with several publicly available tools.

Solution

To establish the recommended configuration via GP, set the following UI path to 'Enabled':


Computer Configuration\Policies\Windows Settings\Security Settings\Account Policies\Password Policy\Password must meet complexity requirements


Impact:
If the default password complexity configuration is retained, additional help desk calls for locked-out accounts could occur because users might not be accustomed to passwords that contain non-alphabetic characters. However, all users should be able to comply with the complexity requirement with minimal difficulty.

If your organization has more stringent security requirements, you can create a custom version of the 'Passfilt.dll' file that allows the use of arbitrarily complex password strength rules. For example, a custom password filter might require the use of non-upper row characters. (Upper row characters are those that require you to hold down the SHIFT key and press any of the digits between 1 and 0.) A custom password filter might also perform a dictionary check to verify that the proposed password does not contain common dictionary words or fragments.

Also, the use of ALT key character combinations can greatly enhance the complexity of a password. However, such stringent password requirements can result in unhappy users and an extremely busy help desk. Alternatively, your organization could consider a requirement for all administrator passwords to use ALT characters in the 0128 - 0159 range. (ALT characters outside of this range can represent standard alphanumeric characters that would not add additional complexity to the password.)

See Also

https://workbench.cisecurity.org/files/1937

Item Details

Category: IDENTIFICATION AND AUTHENTICATION

References: 800-53|IA-5(1), CSCv6|16.5

Plugin: Windows

Control ID: 86a67fb0e212abe1de9b3f2a455f292944cbe7b982696a1bafe5609e24a6d778