By default the install tool password is the one specified during the install. Be sure to change it!
If you don't know the current password, you can set a new one by setting the value of
$TYPO3_CONF_VARS['BE']['installToolPassword'] in typo3conf/LocalConfiguration.php to
the hash value of the password you desire. You can get the hash value of your password
by submitting the desired password with this form.