ImageMagick is free and open-source software used for editing and manipulating digital images. Prior to versions 6.9.13-28 and 7.1.2-2, passing a geometry string containing only a colon (":") to montage -geometry leads GetGeometry() to set width/height to 0. Later, ThumbnailImage() divides by these zero dimensions, triggering a crash (SIGFPE/abort), resulting in a denial of service. This issue has been patched in versions 6.9.13-28 and 7.1.2-2.