gdImageColorMatch in gd_color_match.c in the GD Graphics Library (aka LibGD) 2.2.5 as used in the imagecolormatch function in PHP before 5.6.40 7.x before 7.1.26 7.2.x before 7.2.14 and 7.3.x before 7.3.1 has a heap-based buffer overflow. This can be exploited by an attacker who is able to trigger imagecolormatch calls with crafted image data.