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://www.exploit-db.com/exploits/44876/
https://www.exploit-db.com/exploits/44842/
https://security.gentoo.org/glsa/201808-04