The line that formats the percentage of admins in SpecialStatistics.php divides by the number of users without first checking that it isn't 0. On the off chance that someone has a wiki with no users, this will throw an error.
Version: 1.13.x
Severity: minor
URL: http://svn.wikimedia.org/viewvc/mediawiki/trunk/phase3/includes/SpecialStatistics.php?view=markup