Use-after-free vulnerability in 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, allows remote attackers to execute arbitrary code or cause a denial of service (application crash) via vectors related to a layout change during selection rendering and the DOCUMENT_POSITION_DISCONNECTED attribute in a container of an unspecified type.