WebKit in Apple Safari before 5.0 on Mac OS X 10.5 through 10.6 and Windows, and before 4.1 on Mac OS X 10.4, does not properly perform ordered list insertions, which allows remote attackers to execute arbitrary code or cause a denial of service (memory corruption and application crash) via a crafted HTML document, related to the insertion of an unspecified element into an editable container and the access of an uninitialized element.