The default AFSecurityPolicy.validatesDomainName configuration for AFSSLPinningModeNone in the AFNetworking framework before 2.5.3, as used in the ownCloud iOS Library, disables verification of a server hostname against the domain name in the subject's Common Name (CN) of the X.509 certificate, which allows man-in-the-middle attackers to spoof SSL servers via an arbitrary valid certificate.