[Pkg-openssl-devel] Bug#924621: Bug#924621: openssl 1.1.1b-1 make fetchmail unusable

[Sebastian Andrzej Siewior]

I suggest to close this bug becuase I don't think it is an openssl bug
nor dovecot. The part about minimal key/cipher requirement is already
documented since 1.1.1-2 in NEWS.Debian.gz. The difference between a and
b release is simply that it now the return code is now set properly in
the error case (which cause dovecot to fail).

On 2019-03-18 12:06:59 [+0100], Kurt Roeckx wrote:
> On Mon, Mar 18, 2019 at 01:55:50PM +0900, Atsuhito Kohda wrote:
> > Hi Kurt,
> > 
> > > So from what I understand, the problem is really on the dovecot
> > > side. What does dovecot's log show?
> > > 
> > > Dovecot can configure DH, which seems to default to:
> > > ssl_dh = </usr/share/dovecot/dh.pem
> > > 
> > > That file should be fine, it's 4096 bit.
> > 
> > I generated 4096 bit dh_key:
> > openssl dhparam -out /path/to/dh.pem 4096
> > 
> > then I modified a configuration file of dovecot as follows:
> > ssl_dh=</path/to/dh.pem
> 
> So I assume that somewhere in the past you also did something like
> that, and that the old file was still a 1024 bit file? Or did you
> just not have an ssl_dh line in your config because the old config
> files didn't have it and it wasn't added as part of the upgrade?
> 
> > then I restarted dovecot. Now fetch mail works fine
> > after I upgraded openssl 1.1.1b-1 .
> 
> I have no idea which part of dovecot failed, but I think there
> might still be some other issue.

I think that was related to the part that setting a lower DH key did
fail (like it should) and was just fixed in 1.1.1b.
 
> Do you have any idea which version of TLS is being negotiated?
> Since both use the same version of openssl, it should be able to
> do TLS 1.3 and have used X25519 instead of DHE. It could be that
> some side of the connection for some reasons blocks TLS 1.3.

what happens if you specify allowed ciphers and you don't add the 1.3
ciphers? Then you would fallback to 1.2 because you don't have the 1.3
ciphers or is this case handled different?

> The other reason it can fail is that the change between 1.1.1a and
> 1.1.1b now just caused dovecot to not properly set up TLS. That
> you are in fact not using DHE, but that setting up DHE now failed,
> causing the connection issue.
> 
> 
> Kurt

Sebastian