The WebCore::HTMLLinkElement::process function in WebCore/html/HTMLLinkElement.cpp in WebKit, as used in Apple Safari before 5.0.3 on Mac OS X 10.5 through 10.6 and Windows, and before 4.1.3 on Mac OS X 10.4; webkitgtk before 1.2.6; and possibly other products does not verify whether DNS prefetching is enabled when processing an HTML LINK element, which allows remote attackers to bypass intended access restrictions, as demonstrated by an HTML e-mail message that uses a LINK element for X-Confirm-Reading-To functionality.