A use after free issue exists in WebKit's rendering of a selection when the layout changes. Visiting a maliciously crafted website may lead to an unexpected application termination or arbitrary code execution. This issue is addressed through improved handling of selections.
Trac: http://trac.webkit.org/changeset/52034, http://trac.webkit.org/changeset/55114
Red Hat would like to thank Drew Yao of Apple Product Security for responsibly reporting this issue. Upstream acknowledges wushi of team509, working with TippingPoint's Zero Day Initiative as the original reporter.