ImageMagick's MSL: Stack overflow in ProcessMSLScript

ImageMagick is free and open-source software used for editing and manipulating digital images. Prior to versions 7.1.2-15 and 6.9.13-40, Magick fails to check for circular references between two MSLs, leading to a stack overflow. Versions 7.1.2-15 and 6.9.13-40 contain a patch.