5.1 Security Considerations for Implementers

The CIFS Protocol contains support for NTLM but lacks support for new authentication protocols. The extensions defined in this document offer support for increased security in remote file and printer access via SMB.

In addition to the NTLM challenge/response authentication support, as specified in [MS-CIFS] section, these extensions enable support for Kerberos or any other protocol that can be encapsulated inside the extensible authentication package, as specified in [RFC2743] and [RFC4178].

Extended message signing uses the HMAC_MD5 algorithm, as specified in [RFC2104], to alter the user's session key.

The protocol does not sign oplock break requests from the server to the client if message signing is enabled. This can allow an attacker to affect performance but does not allow an attacker to deny access or alter data.

The algorithm used for message signing has been shown to be subject to collision attacks. See [MD5Collision] for more information.

The new "previous versions" feature potentially allows access to versions of a file that have been deleted or modified. This can provide access to information that was not available without these extensions. However, this access is still subject to the same access checks to which it is normally subject.