cifs module for linux kernel is reported to be actively developed.
Still, as of samba 3.0.27a, there is no documented way to figure the
version of the module `mount.cifs' actually uses.  (If `cifs' kernel
implements such an interface feature for user mode programs, samba
documentation does not say so anyway.)  One has to look at source to
do so.  Generally it will involve pretty complex procedure.

Even in the best, if kernel is built straight from single (upstream)
source package (which nearly never happens in practice), one has to at
least download all of that package (pretty much network bandwidth and
disk space in itself).  If source to build from is obtained in a more
complex way, like applying patches, possibly including complete new
version of the module in question, one generally has to follow all of
that source preparation procedure in binary package build
specification.  (Replacing version bundled with kernel with complete
new one?  After all, what else separate packages linked in
<http://linux-cifs.samba.org/cifs/cifs_download.html> are for?)

So, unless the module reports its version itself, figuring it may be
very time consuming.

Let alone figuring whether binary kernel module implements more
specific features.  (Including, but hardly limited to authentication
with ntlmv2 password hashing.)