browser/browsing_data/browsing_data_remover.cc in Google Chrome before 51.0.2704.63 deletes HPKP pins during cache clearing, which makes it easier for remote attackers to spoof web sites via a valid certificate from an arbitrary recognized Certification Authority.
https://security.gentoo.org/glsa/201607-07
https://codereview.chromium.org/1941073002
https://access.redhat.com/errata/RHSA-2016:1190
http://www.securitytracker.com/id/1035981
http://www.securityfocus.com/bid/90876
http://www.debian.org/security/2016/dsa-3590
http://lists.opensuse.org/opensuse-security-announce/2016-06/msg00005.html
http://lists.opensuse.org/opensuse-security-announce/2016-05/msg00063.html
http://lists.opensuse.org/opensuse-security-announce/2016-05/msg00062.html
http://googlechromereleases.blogspot.com/2016/05/stable-channel-update_25.html