OpenVPN: mark CBC ciphers as weak in WebUI

  CBC a vulnerable to a bunch of vulnerabilities (MAC-then-encrypt,
Padding Oracle, ...) which were considered to be an academic threat.

However, research such as https://blog.qualys.com/technology/2019/04/22/zombie-poodle-and-goldendoodle-vulnerabilities
indicates these issues are more serious. Thereof, this patch marks
remaining CBC ciphers (AES-CBC, SEED-CBC and CAMELLIA-CBC) as "weak";
they should be avoided in future.

It does not change the default, which is AES-256-CBC for compatibility
reasons. Whether this can be changed or not needs to be discussed.

Signed-off-by: Peter Müller <peter.mueller@ipfire.org>
Cc: Erik Kapfer <ummeegge@ipfire.org>
---
 html/cgi-bin/ovpnmain.cgi | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)
  

Hi,

I think I can ACK this although we definitely should change the default. I have raised that a couple of times before.

I also do not like having a very long list of ciphers that are weak. There are not too many left which are “strong”. But yeah, what can you do?

I will wait for Erik to ack this, too.

-Michael

> On 10 Jun 2019, at 19:36, Peter Müller <peter.mueller@ipfire.org> wrote:
> 
> CBC a vulnerable to a bunch of vulnerabilities (MAC-then-encrypt,
> Padding Oracle, ...) which were considered to be an academic threat.
> 
> However, research such as https://blog.qualys.com/technology/2019/04/22/zombie-poodle-and-goldendoodle-vulnerabilities
> indicates these issues are more serious. Thereof, this patch marks
> remaining CBC ciphers (AES-CBC, SEED-CBC and CAMELLIA-CBC) as "weak";
> they should be avoided in future.
> 
> It does not change the default, which is AES-256-CBC for compatibility
> reasons. Whether this can be changed or not needs to be discussed.
> 
> Signed-off-by: Peter Müller <peter.mueller@ipfire.org>
> Cc: Erik Kapfer <ummeegge@ipfire.org>
> ---
> html/cgi-bin/ovpnmain.cgi | 20 ++++++++++----------
> 1 file changed, 10 insertions(+), 10 deletions(-)
> 
> diff --git a/html/cgi-bin/ovpnmain.cgi b/html/cgi-bin/ovpnmain.cgi
> index 439390228..ae1fe8e77 100644
> --- a/html/cgi-bin/ovpnmain.cgi
> +++ b/html/cgi-bin/ovpnmain.cgi
> @@ -2,7 +2,7 @@
> ###############################################################################
> #                                                                             #
> # IPFire.org - A linux based firewall                                         #
> -# Copyright (C) 2007-2014  IPFire Team  <info@ipfire.org>                     #
> +# Copyright (C) 2007-2019  IPFire Team  <info@ipfire.org>                     #
> #                                                                             #
> # This program is free software: you can redistribute it and/or modify        #
> # it under the terms of the GNU General Public License as published by        #
> @@ -4516,7 +4516,7 @@ if ($cgiparams{'TYPE'} eq 'net') {
>     $selected{'DCIPHER'}{'CAST5-CBC'} = '';
>     $selected{'DCIPHER'}{'BF-CBC'} = '';
>     $selected{'DCIPHER'}{'DES-CBC'} = '';
> -    # If no cipher has been chossen yet, select
> +    # If no cipher has been chosen yet, select
>     # the old default (AES-256-CBC) for compatiblity reasons.
>     if ($cgiparams{'DCIPHER'} eq '') {
> 	$cgiparams{'DCIPHER'} = 'AES-256-CBC';
> @@ -4668,13 +4668,13 @@ if ($cgiparams{'TYPE'} eq 'net') {
> 				<option value='AES-256-GCM'		$selected{'DCIPHER'}{'AES-256-GCM'}>AES-GCM (256 $Lang::tr{'bit'})</option>
> 				<option value='AES-192-GCM'		$selected{'DCIPHER'}{'AES-192-GCM'}>AES-GCM (192 $Lang::tr{'bit'})</option>
> 				<option value='AES-128-GCM'		$selected{'DCIPHER'}{'AES-128-GCM'}>AES-GCM (128 $Lang::tr{'bit'})</option>
> -				<option value='CAMELLIA-256-CBC'	$selected{'DCIPHER'}{'CAMELLIA-256-CBC'}>CAMELLIA-CBC (256 $Lang::tr{'bit'})</option>
> -				<option value='CAMELLIA-192-CBC'	$selected{'DCIPHER'}{'CAMELLIA-192-CBC'}>CAMELLIA-CBC (192 $Lang::tr{'bit'})</option>
> -				<option value='CAMELLIA-128-CBC'	$selected{'DCIPHER'}{'CAMELLIA-128-CBC'}>CAMELLIA-CBC (128 $Lang::tr{'bit'})</option>
> -				<option value='AES-256-CBC' 	 	$selected{'DCIPHER'}{'AES-256-CBC'}>AES-CBC (256 $Lang::tr{'bit'}, $Lang::tr{'default'})</option>
> -				<option value='AES-192-CBC' 	 	$selected{'DCIPHER'}{'AES-192-CBC'}>AES-CBC (192 $Lang::tr{'bit'})</option>
> -				<option value='AES-128-CBC' 	 	$selected{'DCIPHER'}{'AES-128-CBC'}>AES-CBC (128 $Lang::tr{'bit'})</option>
> -				<option value='SEED-CBC' 			$selected{'DCIPHER'}{'SEED-CBC'}>SEED-CBC (128 $Lang::tr{'bit'})</option>
> +				<option value='CAMELLIA-256-CBC'	$selected{'DCIPHER'}{'CAMELLIA-256-CBC'}>CAMELLIA-CBC (256 $Lang::tr{'bit'}, $Lang::tr{'vpn weak'})</option>
> +				<option value='CAMELLIA-192-CBC'	$selected{'DCIPHER'}{'CAMELLIA-192-CBC'}>CAMELLIA-CBC (192 $Lang::tr{'bit'}, $Lang::tr{'vpn weak'})</option>
> +				<option value='CAMELLIA-128-CBC'	$selected{'DCIPHER'}{'CAMELLIA-128-CBC'}>CAMELLIA-CBC (128 $Lang::tr{'bit'}, $Lang::tr{'vpn weak'})</option>
> +				<option value='AES-256-CBC' 	 	$selected{'DCIPHER'}{'AES-256-CBC'}>AES-CBC (256 $Lang::tr{'bit'}, $Lang::tr{'default'}, $Lang::tr{'vpn weak'})</option>
> +				<option value='AES-192-CBC' 	 	$selected{'DCIPHER'}{'AES-192-CBC'}>AES-CBC (192 $Lang::tr{'bit'}, $Lang::tr{'vpn weak'})</option>
> +				<option value='AES-128-CBC' 	 	$selected{'DCIPHER'}{'AES-128-CBC'}>AES-CBC (128 $Lang::tr{'bit'}, $Lang::tr{'vpn weak'})</option>
> +				<option value='SEED-CBC' 			$selected{'DCIPHER'}{'SEED-CBC'}>SEED-CBC (128 $Lang::tr{'bit'}, $Lang::tr{'vpn weak'})</option>
> 				<option value='DES-EDE3-CBC'	 	$selected{'DCIPHER'}{'DES-EDE3-CBC'}>DES-EDE3-CBC (192 $Lang::tr{'bit'}, $Lang::tr{'vpn weak'})</option>
> 				<option value='DESX-CBC' 			$selected{'DCIPHER'}{'DESX-CBC'}>DESX-CBC (192 $Lang::tr{'bit'}, $Lang::tr{'vpn weak'})</option>
> 				<option value='DES-EDE-CBC' 		$selected{'DCIPHER'}{'DES-EDE-CBC'}>DES-EDE-CBC (128 $Lang::tr{'bit'}, $Lang::tr{'vpn weak'})</option>
> @@ -5052,7 +5052,7 @@ END
> 		}
>     }
> 
> -#default setzen
> +# set default values
>     if ($cgiparams{'DCIPHER'} eq '') {
> 		$cgiparams{'DCIPHER'} =  'AES-256-CBC';
>     }
> -- 
> 2.16.4
  

Hello Michael,

thanks for your comments.

> Hi,
> 
> I think I can ACK this although we definitely should change the default. I have raised that a couple of times before.
Yes. This is true for IPsec as well... Patch is in my pipeline...
> 
> I also do not like having a very long list of ciphers that are weak. There are not too many left which are “strong”. But yeah, what can you do?
As far as I am concerned, there is little "strong" cryptography left indeed.
It's basically only TLS >= 1.2 with AEAD (e.g. GCM) ciphers and Forward Secrecy.

Speaking about RFC 8446, this is more or less what survived discussions before
standardizing TLS 1.3 ... :-)
> 
> I will wait for Erik to ack this, too.
> 
> -Michael
Thanks, and best regards,
Peter Müller
  

Hi,

> On 10 Jun 2019, at 20:08, Peter Müller <peter.mueller@ipfire.org> wrote:
> 
> Hello Michael,
> 
> thanks for your comments.
> 
>> Hi,
>> 
>> I think I can ACK this although we definitely should change the default. I have raised that a couple of times before.
> Yes. This is true for IPsec as well... Patch is in my pipeline…

Okay. Can we try to make a patchset out of things like this in the future?

That keeps things together and we can coordinate better when we merge this.

We have closed the last Core Update technically last week. Now we have some big changes here and I would prefer to not break the update but have it rather shipped as soon as possible.

>> 
>> I also do not like having a very long list of ciphers that are weak. There are not too many left which are “strong”. But yeah, what can you do?
> As far as I am concerned, there is little "strong" cryptography left indeed.
> It's basically only TLS >= 1.2 with AEAD (e.g. GCM) ciphers and Forward Secrecy.
> 
> Speaking about RFC 8446, this is more or less what survived discussions before
> standardizing TLS 1.3 ... :-)

Yeah I picked up on that too, but we have to make sure that we ensure compatibility.

OpenVPN is hard to update. People cannot migrate from a cipher to another one and not all versions support GCM.

-Michael

>> 
>> I will wait for Erik to ack this, too.
>> 
>> -Michael
> Thanks, and best regards,
> Peter Müller
> -- 
> The road to Hades is easy to travel.
> 	-- Bion of Borysthenes
  

Hi,

On Mo, 2019-06-10 at 20:12 +0100, Michael Tremer wrote:
> Hi,
> 
> > On 10 Jun 2019, at 20:08, Peter Müller <peter.mueller@ipfire.org>
> > wrote:
> > 
> > Hello Michael,
> > 
> > thanks for your comments.
> > 
> > > Hi,
> > > 
> > > I think I can ACK this although we definitely should change the
> > > default. I have raised that a couple of times before.
> > 
> > Yes. This is true for IPsec as well... Patch is in my pipeline…
> 
> Okay. Can we try to make a patchset out of things like this in the
> future?
> 
> That keeps things together and we can coordinate better when we merge
> this.
> 
> We have closed the last Core Update technically last week. Now we
> have some big changes here and I would prefer to not break the update
> but have it rather shipped as soon as possible.
> 
> > > 
> > > I also do not like having a very long list of ciphers that are
> > > weak. There are not too many left which are “strong”. But yeah,
> > > what can you do?
> > 
> > As far as I am concerned, there is little "strong" cryptography
> > left indeed.
> > It's basically only TLS >= 1.2 with AEAD (e.g. GCM) ciphers and
> > Forward Secrecy.
> > 
> > Speaking about RFC 8446, this is more or less what survived
> > discussions before
> > standardizing TLS 1.3 ... :-)
> 
> Yeah I picked up on that too, but we have to make sure that we ensure
> compatibility.
> 
> OpenVPN is hard to update. People cannot migrate from a cipher to
> another one and not all versions support GCM.
A helpful feature for this is --ncp-ciphers where we have had also some
discussions some time ago. In principle it is only a checkbox but
choosing the ciphers is more work also if we want to have a separate
encryption section in the WUI.

Another point which matches this topic i think is the DH-parameter
which is, i think, for updated systems (OpenVPN-2.4.x) useless since
mostly key exchanges are meanwhile managed via ECDH. We tested this
with 'dh none' --> 
https://forum.ipfire.org/viewtopic.php?f=50&t=22664
. But this is again another encryption setting which is also in my
opinion an advanced one in his specifics but a good candidate for a
default. We could also spare then the DH-parameter while PKI generation
(which needs really lot´s of time and can causes also troubles for weak
machines and long paramters). An DH-upload possiblity can still be
there for example to keep the possibility for backwards compatibility).
Did also some work on this but my time is currently really really rare!

> 
> -Michael
> 
> > > 
> > > I will wait for Erik to ack this, too.
I think we have two kinds of "weak" then. The 64bit block ciphers do
have also some technical disadvantage since Sweet32 a renegotiation is
forced after 64MB which can be fast reached. So we have a kind of "very
weak" and "weak" then? 

> > > 
> > > -Michael
> > 
> > Thanks, and best regards,
> > Peter Müller
> > -- 
> > The road to Hades is easy to travel.
> > 	-- Bion of Borysthenes
> 
> 

Some thoughts from here.

Best,

Erik
  

Hi,

> On 10 Jun 2019, at 20:49, ummeegge <ummeegge@ipfire.org> wrote:
> 
> Hi,
> 
> On Mo, 2019-06-10 at 20:12 +0100, Michael Tremer wrote:
>> Hi,
>> 
>>> On 10 Jun 2019, at 20:08, Peter Müller <peter.mueller@ipfire.org>
>>> wrote:
>>> 
>>> Hello Michael,
>>> 
>>> thanks for your comments.
>>> 
>>>> Hi,
>>>> 
>>>> I think I can ACK this although we definitely should change the
>>>> default. I have raised that a couple of times before.
>>> 
>>> Yes. This is true for IPsec as well... Patch is in my pipeline…
>> 
>> Okay. Can we try to make a patchset out of things like this in the
>> future?
>> 
>> That keeps things together and we can coordinate better when we merge
>> this.
>> 
>> We have closed the last Core Update technically last week. Now we
>> have some big changes here and I would prefer to not break the update
>> but have it rather shipped as soon as possible.
>> 
>>>> 
>>>> I also do not like having a very long list of ciphers that are
>>>> weak. There are not too many left which are “strong”. But yeah,
>>>> what can you do?
>>> 
>>> As far as I am concerned, there is little "strong" cryptography
>>> left indeed.
>>> It's basically only TLS >= 1.2 with AEAD (e.g. GCM) ciphers and
>>> Forward Secrecy.
>>> 
>>> Speaking about RFC 8446, this is more or less what survived
>>> discussions before
>>> standardizing TLS 1.3 ... :-)
>> 
>> Yeah I picked up on that too, but we have to make sure that we ensure
>> compatibility.
>> 
>> OpenVPN is hard to update. People cannot migrate from a cipher to
>> another one and not all versions support GCM.
> A helpful feature for this is --ncp-ciphers where we have had also some
> discussions some time ago. In principle it is only a checkbox but
> choosing the ciphers is more work also if we want to have a separate
> encryption section in the WUI.

Do we have any implementation of this somewhere?

Right now this feature is enabled and will default to what ever the OpenVPN project thinks is right, but the option on the web UI does not really matter any more. The cipher selected here is only being used when you have an old client which does not know about ncp-ciphers, yet.

> Another point which matches this topic i think is the DH-parameter
> which is, i think, for updated systems (OpenVPN-2.4.x) useless since
> mostly key exchanges are meanwhile managed via ECDH. We tested this
> with 'dh none' --> 
> https://forum.ipfire.org/viewtopic.php?f=50&t=22664

When you say most, how many is that? One is enough to have the DH params.

> . But this is again another encryption setting which is also in my
> opinion an advanced one in his specifics but a good candidate for a
> default. We could also spare then the DH-parameter while PKI generation
> (which needs really lot´s of time and can causes also troubles for weak
> machines and long paramters). An DH-upload possiblity can still be
> there for example to keep the possibility for backwards compatibility).
> Did also some work on this but my time is currently really really rare!

Yes, I think we can safely move to EC crypto for modern clients. The question is only how we can keep to support older clients. OpenVPN makes this very very very very difficult.

> 
>> 
>> -Michael
>> 
>>>> 
>>>> I will wait for Erik to ack this, too.
> I think we have two kinds of "weak" then. The 64bit block ciphers do
> have also some technical disadvantage since Sweet32 a renegotiation is
> forced after 64MB which can be fast reached. So we have a kind of "very
> weak" and "weak" then? 

In essence you are right. But isn’t weak just another word for broken? And is something either broken or not? I think it does not matter how weak something is really. The message we want to get across to users is to not use these ciphers any more. Having something as “weak” next to “very weak” might make it sound a bit softer and that it might be a little bit acceptable to use the weak cipher.

> 
>>>> 
>>>> -Michael
>>> 
>>> Thanks, and best regards,
>>> Peter Müller
>>> -- 
>>> The road to Hades is easy to travel.
>>> 	-- Bion of Borysthenes
>> 
>> 
> 
> Some thoughts from here.
> 
> Best,
> 
> Erik