Stack-based buffer overflow in the flattenIncrementally function in flatten.c in xcftools 1.0.4, as reachable from the (1) xcf2pnm and (2) xcf2png utilities, allows remote attackers to cause a denial of service (crash) and possibly execute arbitrary code via a crafted image that causes a conversion to a location "above or to the left of the canvas." NOTE: some of these details are obtained from third party information.