The OpenID module in Drupal 6.x before 6.36 and 7.x before 7.38 allows remote attackers to log into other users' accounts by leveraging an OpenID identity from certain providers, as demonstrated by the Verisign, LiveJournal, and StackExchange providers.
https://www.drupal.org/SA-CORE-2015-002
http://www.securityfocus.com/bid/75294
http://www.debian.org/security/2015/dsa-3291
http://lists.fedoraproject.org/pipermail/package-announce/2015-July/161265.html
http://lists.fedoraproject.org/pipermail/package-announce/2015-July/161261.html