The imagetruecolortopalette function in ext/gd/gd.c in PHP before 5.6.25 and 7.x before 7.0.10 does not properly validate the number of colors, which allows remote attackers to cause a denial of service (select_colors allocation error and out-of-bounds write) or possibly have unspecified other impact via a large value in the third argument. http://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2016-7126
