Fedora Info: [389-users] Re: minssf and TLS cipher ordering

As a follow up to William's suggestion of setting the global crypto policy to FUTURE:

This does work but only because the AES128 ciphers are completely removed from the global NSS policies. So it doesn't actually fix the problem, it just masks it (and who knows where else it will pop up).

On Wed, Apr 28, 2021 at 8:29 AM Trevor Vaughan <tvaughan@onyxpoint.com> wrote:

Interestingly, if I remove the cipher specification, I get the result of ECDHE-RSA-AES128-GCM-SHA256.

Can you see if this also happens with your version of nss?

Thanks,

Trevor

On Wed, Apr 28, 2021 at 8:27 AM Trevor Vaughan <tvaughan@onyxpoint.com> wrote:
So, I just ran this test with selfserv as you have above and everything worked as expected with s_client.

It seems to be something in 389 itself.

On Tue, Apr 27, 2021 at 6:32 PM Rob Crittenden <rcritten@redhat.com> wrote:
Trevor Vaughan wrote:
> Going full circle on this, I confirmed using s_client that what I was
> seeing was indeed happening but not for the reason that I thought it was.
>
> Given that the min_ssf is 256, the connection requires a 256-bit cipher
> and hash to communicate with the server.
>
> Strangely, the internal strength logic on the 389-DS side appears to
> pick ECDHE-RSA-AES128-GCM-SHA256 *before* ECDHE-RSA-AES256-GCM-SHA384.
> Likewise, if I add any of the AES128 ciphers to the list after the
> AES256 ciphers, one of the 128-bit ciphers will be chosen first. This
> seems incorrect given that the server should be using the strongest
> cipher suite available if possible.
>
> The client cipher order preference is completely ignored (which is fine).
>
> As pointed out in the last response, I did indeed need to explicitly
> enable only the 256-bit+ hash/cipher combinations in the
> confusingly-named nsSSL3Ciphers attribute.
>
> After figuring this out and dumping the internal supported cipher list,
> I can confirm that the ciphers in the nsSSL3Ciphers list are the only
> ones that are presented to the client.
>
> While not ideal, this does provide a solution to the issue where I don't
> have to tell all system users that they need to nail up the cipher lists
> on the client side in order for things to function properly.
>
> But that leaves me with two questions:
>
> 1) Why, when the nsslapd-minssf option is set in the global
> configuration, does 389-DS not automatically prune any options that will
> result in an unsuccessful connection.
>
> 2) Why is the internal cipher sorting order choosing weaker cipher
> suites before stronger ones?

I'm pretty sure that 389-ds still uses NSS for server-side crypto and
unless something has changed NSS doesn't do cipher sorting. It picks the
"best" for you. AFAIR the server has no say in the matter.

But, as a goof I used a pure NSS server tool to see what happens and it
picked the expected cipher.

Enable your two ciphers (in hex form):

$ /usr/lib64/nss/unsupported-tools/selfserv -n Server-Cert -d
/etc/dirsrv/slapd-EXAMPLE-TEST/ -p 8389 -f
/etc/dirsrv/slapd-EXAMPLE-TEST/pwdfile.txt -c :C02F -c :C030 -v -V
tls1.2:tls1.2

run s_client:

New, TLSv1.2, Cipher is ECDHE-RSA-AES256-GCM-SHA384
Server public key is 2048 bit
Secure Renegotiation IS supported
Compression: NONE
Expansion: NONE
No ALPN negotiated
SSL-Session:
Protocol : TLSv1.2
Cipher : ECDHE-RSA-AES256-GCM-SHA384
Session-ID:
2AF9EFDDB3EA99C101C4E4F99A47CD479D294C15309D7E994ADA21C083D8E096
Session-ID-ctx:
Master-Key:
85646A59B24D5A88080227BD59E328C688910FB0B2E2BAD77D7B1A96F6A9A3ACBF74EEC6C844A7D59527152928580743
PSK identity: None
PSK identity hint: None
SRP username: None
Start Time: 1619562457
Timeout : 7200 (sec)
Verify return code: 0 (ok)
Extended master secret: yes

So even more confusing unless I've goofed something up, sorry. I didn't
mess with minssf, maybe that does make a difference.

The ciphers are:

TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 0xC02F
TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 0xC030

Don't mean to stir up the mud but this may be a question for the NSS team.

rob

> On Mon, Apr 26, 2021 at 11:50 PM William Brown <wbrown@suse.de
> <mailto:wbrown@suse.de>> wrote:
>
> Then youll need to disable everything except aes256 then I suspect
> ... :(
>
> > On 25 Apr 2021, at 11:39, Trevor Vaughan <tvaughan@onyxpoint.com
> <mailto:tvaughan@onyxpoint.com>> wrote:
> >
> > Well, in this case, I've got to be able to work with regulatory
> requirements so not much I can do there.
> >
> > Trevor
> >
> > On Sat, Apr 24, 2021, 9:03 PM William Brown <wbrown@suse.de
> <mailto:wbrown@suse.de>> wrote:
> >
> >
> > > On 24 Apr 2021, at 22:30, Trevor Vaughan <tvaughan@onyxpoint.com
> <mailto:tvaughan@onyxpoint.com>> wrote:
> > >
> > > Hi Marc,
> > >
> > > I was under the impression that it would pick the highest
> supported, but that doesn't seem to be what is happening based on my
> previous example.
> > >
> > > Instead, it seems to just be picking the first compatible,
> regardless of strength.
> >
> > It choose aes128 over 256 because of processing speed, and "strong
> enough".
> >
> > >
> > > Trevor
> > >
> > > On Fri, Apr 23, 2021, 10:03 PM Marc Sauton <msauton@redhat.com
> <mailto:msauton@redhat.com>> wrote:
> > > about ciphers order and TLS cipher suite discovery, NSS will
> pick the one with highest strength from the available ciphers, and
> compatible with the TLS client ( handshake)
> > >
> > > you can check the configuration with for example (replace the
> string m1 with an instance name):
> > > dsconf m1 security get
> > > dsconf m1 security ciphers list
> > > dsconf m1 security ciphers list --supported | less
> > > dsconf m1 security ciphers list --enabled
> > > ldapsearch -o ldif-wrap=no -LLLxD "cn=Directory Manager" -W -b
> cn=encryption,cn=config | less
> > >
> > > and to set ciphers (can be "delicate"):
> > > /usr/lib64/nss/unsupported-tools/listsuites | grep -B1
> --no-group-separator "Enabled" | less
> > > dsconf m1 security ciphers set xxxxx
> > >
> > > doc ref:
> > >
> https://access.redhat.com/documentation/en-us/red_hat_directory_server/11/html/administration_guide/enabling_tls#setting_encryption_ciphers
> > >
> > > and NSS source:
> > > ./lib/ssl/ssl3con.c
> > > ./lib/ssl/sslenum.c
> > >
> > >
> > > On Fri, Apr 23, 2021 at 4:57 PM Trevor Vaughan
> <tvaughan@onyxpoint.com <mailto:tvaughan@onyxpoint.com>> wrote:
> > > William,
> > >
> > > I do apologize! I'll keep that in mind in the future.
> > >
> > > Thanks again for your help,
> > >
> > > Trevor
> > >
> > > On Fri, Apr 23, 2021, 7:50 PM William Brown <wbrown@suse.de
> <mailto:wbrown@suse.de>> wrote:
> > > Sorry to call this out, but my name is "William" not "Bill". I
> have personal reasons to dislike being called that name.
> > >
> > > Regardless, happy to help out :)
> > >
> > > > On 23 Apr 2021, at 22:11, Trevor Vaughan
> <tvaughan@onyxpoint.com <mailto:tvaughan@onyxpoint.com>> wrote:
> > > >
> > > > Bill and Pierre,
> > > >
> > > > Thanks for the responses!
> > > >
> > > > It sounds like I have to figure out how to configure the NSS
> library for 389-DS specifically.
> > > >
> > > > In EL8+ I know that I can configure the global crypto policy
> but I'm hoping that I can do it for the specific application. I
> haven't found anything in the documentation so far but at least this
> gets me pointed in the right direction.
> > > >
> > > > Thanks,
> > > >
> > > > Trevor
> > > >
> > > > On Fri, Apr 23, 2021 at 4:42 AM Pierre Rogier
> <progier@redhat.com <mailto:progier@redhat.com>> wrote:
> > > > Hi Trevor,
> > > >
> > > > I do not think it is possible to specify the cypher order
> negotiation:
> > > > I am not sure whether TLS protocol allow to specify an
> order when negotiating the cypher,
> > > > but at 389 level there is no way to specify an order:
> > > > The NSS security layer provides the list of supported cypher
> and 389 use
> > > > nsSSL3Ciphers config parameter to enable/disable theses
> cyphers in the list (without changing the order)
> > > >
> > > > So my feeling is that if there is an order it is up to the
> different
> > > > security layer implementations and may differs between
> the applications,
> > > >
> > > > Regards,
> > > > Pierre
> > > >
> > > > On Thu, Apr 22, 2021 at 7:28 PM Trevor Vaughan
> <tvaughan@onyxpoint.com <mailto:tvaughan@onyxpoint.com>> wrote:
> > > > Hi William,
> > > >
> > > > In terms of the STARTTLS bits (in theory) properly configuring
> your client software mitigates the password leak risk. But this also
> happens with pure (non-RFC) LDAPS connections.
> > > >
> > > > The docs note that minssf applies to the crypto required bits
> as well as the SASL layer.
> > > >
> > > > Ignoring most of that, my issue is that I don't understand why
> I have to nail my client software to ciphers explicitly known by
> 389-DS instead of the two negotiating the strongest things possible
> out of the gate.
> > > >
> > > > For instance, if I use AES256 with a minssf=256, everything
> works just fine.
> > > >
> > > > But, if I use AES128:AES256:@STRENGTH (which should sort
> strongest to weakest) then access is denied.
> > > >
> > > > How do I get 389-DS to negotiate the strongest ciphers first
> (regardless of the method)?
> > > >
> > > > Thanks,
> > > >
> > > > Trevor
> > > >
> > > > On Wed, Apr 21, 2021 at 7:34 PM William Brown <wbrown@suse.de
> <mailto:wbrown@suse.de>> wrote:
> > > > Hi there,
> > > >
> > > > > On 22 Apr 2021, at 03:52, Trevor Vaughan
> <tvaughan@onyxpoint.com <mailto:tvaughan@onyxpoint.com>> wrote:
> > > > >
> > > > > Hi All,
> > > > >
> > > > > OS Version: CentOS 8
> > > > > 389-DS Version: 1.4.3.22 from EPEL
> > > > >
> > > > > I have a server set up with minssf=256 and have been
> surprised that either 389-DS, or openssl, does not appear to be
> doing what I would consider a logical TLS negotiation.
> > > > >
> > > > > I had thought that the system would start with the strongest
> cipher and then negotiate down to something that was acceptable.
> > > > >
> > > > > Instead, I'm finding that I have to nail up the ciphers to
> something that the 389-DS server both recognizes and is within the
> expected SSF.
> > > > >
> > > > > Is this expected behavior or do I have something configured
> incorrectly?
> > > >
> > > > That's not what minssf does.
> > > >
> > > > minssf says "during a bind operation, reject if the encryption
> strength used is less than 256 bits or equivalent".
> > > >
> > > > The "bit strength" is arbitrary though, because it's a concept
> from sasl, and generally is very broken.
> > > >
> > > > Remember, minssf does NOT do what you think though! Because
> bind is the *first* message on the wire, the series of operations is
> > > >
> > > >
> > > > client server
> > > > open plain text conn ->
> > > > <- accept connection
> > > > send bind on conn ->
> > > > <- reject due to minsff too weak.
> > > >
> > > >
> > > > So you have already leaked the password!
> > > >
> > > >
> > > > The only way to ensure this does not occur is to set
> "nsslapd-port: 0" which disables plaintext. Then you *only* use
> ldaps on port 636, which is guarantee encrypted from the start.
> > > >
> > > > It is worth noting that the use of starttls over ldap, does
> *NOT* mitigate this issue, for a similar reason.
> > > >
> > > >
> > > > Caveat: If you are using kerberos/gssapi you can NOT disable
> plaintext ldap due to these protocols attempting to install their
> own encryption layers.
> > > >
> > > >
> > > > Hope that helps,
> > > >
> > > >
> > > > >
> > > > > Thanks,
> > > > >
> > > > > Trevor
> > > > >
> > > > > --
> > > > > Trevor Vaughan
> > > > > Vice President, Onyx Point, Inc
> > > > > (410) 541-6699 x788
> > > > >
> > > > > -- This account not approved for unencrypted proprietary
> information --
> > > > > _______________________________________________
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> > > >
> > > > —
> > > > Sincerely,
> > > >
> > > > William Brown
> > > >
> > > > Senior Software Engineer, 389 Directory Server
> > > > SUSE Labs, Australia
> > > > _______________________________________________
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> > > >
> > > > --
> > > > Trevor Vaughan
> > > > Vice President, Onyx Point, Inc
> > > > (410) 541-6699 x788
> > > >
> > > > -- This account not approved for unencrypted proprietary
> information --
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> > > >
> > > > --
> > > > --
> > > >
> > > > 389 Directory Server Development Team
> > > > _______________________________________________
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> > > >
> > > > --
> > > > Trevor Vaughan
> > > > Vice President, Onyx Point, Inc
> > > > (410) 541-6699 x788
> > > >
> > > > -- This account not approved for unencrypted proprietary
> information --
> > > > _______________________________________________
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> > > —
> > > Sincerely,
> > >
> > > William Brown
> > >
> > > Senior Software Engineer, 389 Directory Server
> > > SUSE Labs, Australia
> > > _______________________________________________
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> > —
> > Sincerely,
> >
> > William Brown
> >
> > Senior Software Engineer, 389 Directory Server
> > SUSE Labs, Australia
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> —
> Sincerely,
>
> William Brown
>
> Senior Software Engineer, 389 Directory Server
> SUSE Labs, Australia
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>
>
> --
> Trevor Vaughan
> Vice President, Onyx Point, Inc
> (410) 541-6699 x788
>
> -- This account not approved for unencrypted proprietary information --
>
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--
Trevor Vaughan
Vice President, Onyx Point, Inc
(410) 541-6699 x788

-- This account not approved for unencrypted proprietary information --

--
Trevor Vaughan
Vice President, Onyx Point, Inc
(410) 541-6699 x788

-- This account not approved for unencrypted proprietary information --

Trevor Vaughan
Vice President, Onyx Point, Inc

(410) 541-6699 x788

-- This account not approved for unencrypted proprietary information --

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Wednesday, April 28, 2021

[389-users] Re: minssf and TLS cipher ordering

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