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5.3.3.2.1 Ensure password number of changed characters is configured

Information

The pwquality difok option sets the number of characters in a password that must not be present in the old password.

Use of a complex password helps to increase the time and resources required to compromise the password. Password complexity, or strength, is a measure of the effectiveness of a password in resisting attempts at guessing and brute-force attacks.

Password complexity is one factor of several that determines how long it takes to crack a password. The more complex the password, the greater the number of possible combinations that need to be tested before the password is compromised.

Solution

Create or modify a file ending in .conf in the /etc/security/pwquality.conf.d/ directory or the file /etc/security/pwquality.conf and add or modify the following line to set difok to 2 or more. Ensure setting conforms to local site policy:

Example:

#!/usr/bin/env bash

{
 sed -ri 's/^\s*difok\s*=/# &/' /etc/security/pwquality.conf
 [ ! -d /etc/security/pwquality.conf.d/ ] && mkdir /etc/security/pwquality.conf.d/
 printf '\n%s' "difok = 2" > /etc/security/pwquality.conf.d/50-pwdifok.conf
}

Run the following command:

# grep -Pl -- '\bpam_pwquality\.so\h+([^#\n\r]+\h+)?difok\b' /usr/share/pam-configs/*

Edit any returned files and remove the difok argument from the pam_pwquality.so line(s):

Impact:

Requiring a minimum number of changed characters from the previous password reduces the risk of incremental password changes (e.g., changing only one character) that allow users to effectively reuse their previous password.

See Also

https://workbench.cisecurity.org/benchmarks/27797

Item Details

Category: IDENTIFICATION AND AUTHENTICATION

References: 800-53|IA-5, 800-53|IA-5(1), CSCv7|4.4

Plugin: Unix

Control ID: 2dcea06e2631c8faa5aebd0f6ac8f95d930c9572b1298759989a20ea34990155