Re: [gentoo-user] openssh-7.1_p1-r2 won't allow "nxserver" to connect

[Mick <michaelkintzios@gmail.com>]

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On Saturday 14 Nov 2015 06:49:22 thelma@sys-concept.com wrote:
> Thelma
> 
> On 11/13/2015 11:08 PM, thelma@sys-concept.com wrote:
> > I'm running: nxserver-freenx-0.7.3_p104-r7
> > After recent upgrade, system installed new stable openssh-7.1_p1-r2
> > 
> > The problem is the new openssh-7.1_p1-r2 will not allow my my "nxserver"
> > to connect, I get an error: Permission denied
> > (publickey,keyboard-interactive) see below:
> > 
> > nxsetup --test
> > ...
> > <---- done
> > 
> > ----> Testing your nxserver connection ...
> > Permission denied (publickey,keyboard-interactive).
> > Fatal error: Could not connect to NX Server.
> > 
> > Please check your ssh setup:
> > 
> > The following are _examples_ of what you might need to check.
> > 
> > 	- Make sure "nx" is one of the AllowUsers in sshd_config.
> > 	
> >     (or that the line is outcommented/not there)
> > 	
> > 	- Make sure "nx" is one of the AllowGroups in sshd_config.
> > 	
> >     (or that the line is outcommented/not there)
> > 	
> > 	- Make sure your sshd allows public key authentication.
> > 	- Make sure your sshd is really running on port 22.
> > 	- Make sure your sshd_config AuthorizedKeysFile in sshd_config is set 
to
> > 	authorized_keys2.
> > 	
> >     (this should be a filename not a pathname+filename)
> >   
> >   - Make sure you allow ssh on localhost, this could come from some
> >   
> >     restriction of:
> >       -the tcp wrapper. Then add in /etc/hosts.allow: ALL:localhost
> >       
> >       -the iptables. add to it:
> >          $ iptables -A INPUT  -i lo -j ACCEPT
> >          $ iptables -A OUTPUT -o lo -j ACCEPT
> > 
> > What I should be getting is this:
> > ----> Testing your nxserver connection ...
> > HELLO NXSERVER - Version 3.2.0-74-TEAMBZR104 OS (GPL, using backend:
> > 3.5.0) NX> 105 quit
> > Quit
> > NX> 999 Bye
> > <--- done
> > 
> > I did not change anything in sshd_config.
> > But I downgraded to: openssh-6.9_p1-r2 and nxserver connects OK.
> > 
> > What could be the problem with new: openssh-7.1_p1-r2
> 
> I think the reason is that OpenSSH 7.0 disables ssh-dss keys by default
> https://www.gentoo.org/support/news-items/2015-08-13-openssh-weak-keys.html
> 
> And and nxserver is using ssh-dss keys by default.
> 
> I have to find a way a way to replace the ssh-dss key in: /etc/nxserver/
> with RSA one.
> 
> Do I just run: ssh-keygen -t rsa
> and copy the key pair to /etc/nxserver/ directory?
> 
> --
> Thelma

Since openssh-7.0 DSS keys are disabled and about time too!

==========================================================
if has_version "<${CATEGORY}/${PN}-7.1_p1" ; then #557388
        elog "Starting with openssh-7.0, support for ssh-dss keys were 
disabled due to their"
        elog "weak sizes.  If you rely on these key types, you can re-enable 
the key types by"
        elog "adding to your sshd_config:"
        elog "  PubkeyAcceptedKeyTypes=+ssh-dss"
        elog "You should however generate new keys using rsa or ed25519."
fi
==========================================================


Also SHA1 hashes are disabled and you will get errors like these when you try 
to login to a server which is still using deprecated ciphers:

Unable to negotiate with XXX.XX.XXX.X: no matching host key type found. Their 
offer: ssh-dss

Unable to negotiate with XXX.XX.XXX.X: no matching key exchange method found. 
Their offer: diffie-hellman-group1-sha1

If this is within your LAN and therefore relatively protected, you could 
specify deprecated ciphers and hashes like so:

ssh -o KexAlgorithms=+diffie-hellman-group1-sha1 -o HostKeyAlgorithms=+ssh-dss 
my_user@XXX.XX.XXX.X


Alternatively, after you create a strong prime:

ssh-keygen -t rsa -b 4096


or probably better to use ed25519:

ssh-keygen -t ed25519

HTH.
-- 
Regards,
Mick

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