Cis GCP Cos 5.2.3

5.2.3 Ensure password hashing algorithm is SHA-512 (Manual)

Description

The commands below change password encryption from md5 to sha512 (a much stronger hashing algorithm). All existing accounts will need to perform a password change to upgrade the stored hashes to the new algorithm.

Rationale

The SHA-512 algorithm provides much stronger hashing than MD5, thus providing additional protection to the system by increasing the level of effort for an attacker to successfully determine passwords.

Note that these changes only apply to accounts configured on the local system.

Audit Procedure

Verify password hashing algorithm is sha512. This setting is commonly configured with the pam_unix.so sha512 option found in /etc/pam.d/common-password or /etc/pam.d/system-auth and /etc/pam.d/password-auth. Example:

password required pam_unix.so sha512

Expected Result

The pam_unix.so module should include the sha512 option in the PAM password configuration.

Remediation

Set password hashing algorithm to sha512. Many distributions provide tools for updating PAM configuration, consult your documentation for details. If no tooling is provided edit the appropriate /etc/pam.d/ configuration file and add or modify the pam_unix.so lines to include the sha512 option:

password required pam_unix.so sha512

Additional Information:

Consult your documentation for the appropriate PAM file and module.

Additional module options may be set, recommendation only covers those listed here.

If it is determined that the password algorithm being used is not SHA-512, once it is changed, it is recommended that all user ID's be immediately expired and forced to change their passwords on next login. To accomplish that, the following commands can be used. Any system accounts that need to be expired should be carefully done separately by the system administrator to prevent any potential problems.

# cat /etc/passwd | awk -F: '( $3 >= 500 && $1 != "nfsnobody" ) { print $1 }' | xargs -n 1 chage -d 0

This command assumes a system UID split at 500. Some distributions split at UID 1000 instead, consult your documentation and/or the UID_MIN setting in /etc/login.defs to determine which is appropriate for you.

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