by Pavel Krejci.
Easiest solution would be to edit Moodle library file lib/moodlelib.php in plain-text editor. Backup the original file before editing.
find the line which reads:
function validate_internal_user_password($user, $password) {
add the following 1 line below it:
return true;
save it and voila - any password goes. Revert the change after you reset your Moodle password ASAP to keep the site secure.