Re: TLS, integrity and root DSE

["Michael StrÃder" <michael@stroeder.com>]

On Wed, 24 Jul 2013 07:59:21 -0700 Quanah Gibson-Mount <quanah@zimbra.com>
wrote
> --On Wednesday, July 24, 2013 4:08 PM +0200 Ulrich Windl 
> <Ulrich.Windl@rz.uni-regensburg.de> wrote:
> 
> > Hi!
> >
> > When trying to require integrity for LDAP connections by specifying
> > "ssf=1" in Security, I have a problem with Perl where the cat bites its
> > tail:
> >
> > It's recommended to query the root DSE for TLS extension before trying to
> > use TLS like this:
> >
> > my $dse = $ldap->root_dse();
> >
> > if ($dse->supported_extension(LDAP_EXTENSION_START_TLS)) {
> >         my $msg = $ldap->start_tls('verify' => 'require',
> >                                    'capath' => '/etc/ssl/certs');
> > ...
> 
> Personally, I just always try to startTLS regardless.  Then you can decide 
> whether or not you wish to continue after that point based on whether or 
> not it succeeds or fails.

>From RFC 2830, section 6 "Security Considerations":

                           Additionally, an active-intermediary
   attacker can remove the Start TLS extended operation from the
   supportedExtension attribute of the root DSE.

=> Always try startTLS at the client side if set in local configuration.

Furthermore from this section:

   Therefore, both parties
   SHOULD independently ascertain and consent to the security level
   achieved once TLS is established and before beginning use of the TLS
   connection. For example, the security level of the TLS connection
   might have been negotiated down to plaintext.

So your client has to query the effective security level from the LDAP API and
make a decision based on comparison to local config. Not sure which option to
use in case of TLS though.

Ciao, Michael.