The GenericConsumer class in the Consumer component in ZendOpenId before 2.0.2 and the Zend_OpenId_Consumer class in Zend Framework 1 before 1.12.4 violate the OpenID 2.0 protocol by ensuring only that at least one field is signed, which allows remote attackers to bypass authentication by leveraging an assertion from an OpenID provider.
http://www.securityfocus.com/bid/66358
http://www.mandriva.com/security/advisories?name=MDVSA-2014:072
http://www.debian.org/security/2015/dsa-3265
http://seclists.org/oss-sec/2014/q2/0