The gdImageCropThreshold function in gd_crop.c in the GD Graphics Library (aka libgd) before 2.2.3, as used in PHP before 7.0.9, allows remote attackers to cause a denial of service (application crash) via an invalid color index.
The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.