Integer signedness error in (1) QuickLook in Apple Mac OS X 10.5.5 and (2) Office Viewer in Apple iPhone OS 1.0 through 2.1 and iPhone OS for iPod touch 1.1 through 2.1 allows remote attackers to cause a denial of service (application termination) and execute arbitrary code via a crafted Microsoft Excel file that triggers an out-of-bounds memory access, related to "handling of columns."