The HTTP/2 protocol does not consider the role of the TCP congestion window in providing information about content length, which makes it easier for remote attackers to obtain cleartext data by leveraging a web-browser configuration in which third-party cookies are sent, aka a “HEIST” attack.
arstechnica.com/security/2016/08/new-attack-steals-ssns-e-mail-addresses-and-more-from-https-pages/
www.securityfocus.com/bid/92773
www.securitytracker.com/id/1036741
www.securitytracker.com/id/1036742
www.securitytracker.com/id/1036743
www.securitytracker.com/id/1036744
www.securitytracker.com/id/1036745
www.securitytracker.com/id/1036746
tom.vg/papers/heist_blackhat2016.pdf