Prior to Apache HTTP release 2.4.25, mod_sessioncrypto was encrypting its data/cookie using the configured ciphers with possibly either CBC or ECB modes of operation (AES256-CBC by default), hence no selectable or builtin authenticated encryption. This made it vulnerable to padding oracle attacks, particularly with CBC. An authentication tag (SipHash MAC) is now added to prevent such attacks. https://httpd.apache.org/security/vulnerabilities_24.html http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-0736
