How to change all Magento admin passwords

It is recommended to use at least 10- character, computer generated passwords. In case of a breach, you can assume that all passwords have been intercepted, so they should be changed as soon as possible. The following CLI script may help:

n98=n98-magerun2
$n98 admin:user:list --format=csv | grep ,active | while read row;
do
     user=$(echo $row | cut -d, -f2)
     pass=$(tr -cd '[:alnum:]' < /dev/urandom | fold -w10 | head -n1)
     echo "$user -> $pass"
     $n98 admin:user:change-password "$user" $pass >/dev/null
done

Use n98-magerun for Magento 1.

Don't forget to also change passwords for:

1. Your database (update env.php/local.xml/wp-config.php as well)
2. Your hosting account: both your server and your control panel. Also make sure that no malicious SSH keys have been added.

After a breach, changing passwords is not enough on its own. Also rotate the Magento crypt key and delete any unknown API integrations, since their tokens are stored in the database and survive both password and key rotation.