Set default password for every user in WordPress

kr_default_password_after_login.php

<?php
add_action('user_register', 'kr_alter_password', 10, 1);
function kr_alter_password($user_id) {
	// user email. $user return full user info
	// new entered password (plain text)
	if ( $user_id ) {
		wp_set_password( "[your-password]", $user_id );
	}
}