Integer signedness error in the dynamicGetbuf function in gd_io_dp.c in the GD Graphics Library (aka libgd) through 2.2.3, as used in PHP before 5.6.28 and 7.x before 7.0.13, allows remote attackers to cause a denial of service (stack-based buffer overflow) or possibly have unspecified other impact via a crafted imagecreatefromstring call.
https://support.f5.com/csp/article/K21336065?utm_source=f5support&%3Butm_medium=RSS
https://github.com/libgd/libgd/commit/53110871935244816bbb9d131da0bccff734bfe9
https://bugs.php.net/bug.php?id=73280
http://www.securityfocus.com/bid/93594
http://www.php.net/ChangeLog-7.php
http://www.php.net/ChangeLog-5.php