I have found and reported an out of bounds memory read in PHP:
https://bugs.php.net/bug.php?id=73825
It affected all three supported versions and has been fixed with the latest updates:
https://secure.php.net/ChangeLog-5.php#5.6.30
https://secure.php.net/ChangeLog-7.php#7.0.15
https://secure.php.net/ChangeLog-7.php#7.1.1