The updated packages fix security vulnerabilities:
gdgifin.c in the GD Graphics Library (aka libgd), as used in PHP before 5.6.33, 7.0.x before 7.0.27, 7.1.x before 7.1.13, and 7.2.x before 7.2.1, has an integer signedness error that leads to an infinite loop via a crafted GIF file, as demonstrated by a call to the imagecreatefromgif or imagecreatefromstring PHP function. This is related to GetCode_ and gdImageCreateFromGifCtx (CVE-2018-5711).
Libgd version 2.2.5 contains a Double Free Vulnerability vulnerability in gdImageBmpPtr Function that can result in Remote Code Execution . This attack appear to be exploitable via Specially Crafted Jpeg Image can trigger double free (CVE-2018-1000222).