webkitFaviconDatabaseSetIconForPageURL and webkitFaviconDatabaseSetIconURLForPageURL in UIProcess/API/glib/WebKitFaviconDatabase.cpp in WebKit, as used in WebKitGTK+ through 2.21.3, mishandle an unset pageURL, leading to an application crash.
https://bugzilla.gnome.org/show_bug.cgi?id=795740
https://security.gentoo.org/glsa/201808-04