The load_tile function in the XCF coder in coders/xcf.c in (1) ImageMagick 6.2.8-0 and (2) GraphicsMagick (aka gm) 1.1.7 allows user-assisted remote attackers to cause a denial of service (crash) or possibly execute arbitrary code via a crafted .xcf file that triggers an out-of-bounds heap write, possibly related to the ScaleCharToQuantum function.
CWE-119