org.apache.http.conn.ssl.AbstractVerifier in Apache HttpComponents HttpClient before 4.3.5 and HttpAsyncClient before 4.0.2 does not properly verify that the server hostname matches a domain name in the subject's Common Name (CN) or subjectAltName field of the X.509 certificate, which allows man-in-the-middle attackers to spoof SSL servers via a "CN=" string in a field in the distinguished name (DN) of a certificate, as demonstrated by the "foo,CN=www.apache.org" string in the O field.