A use after free issue exists in WebKit's handling of the ':first-letter' pseudo-element in cascading stylesheets. Visiting a maliciously crafted website may lead to an unexpected application termination or arbitrary code execution. This issue is addressed through improved handling of the ':first-letter' pseudo-element.
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.