Re: Bug#499774: starttls is a joke

[Matthias Andree <matthias.andree@gmx.de>]

Reiner Steib <reinersteib+gmane@imap.cc> writes:

>> Then, someone should correct the code to support passing trust anchors,
>> allow passing the verify value, and document capabilities and
>> limitations. 
>
> Gnus currently uses starttls if starttls and gnutls-cli are available
> for backward compatibility.  
>
> Would it make sense to prefer gnutls-cli and warn when using starttls
> (if gnutls-cli is not installed)?

It would make sense to fix the tools first, and stop using them in
unsafe ways.

I recently found on Cygwin, when setting up Emacs+Gnus, that gnutls-cli
(2.4.2 IIRC) has some subtle "accept b0rked cert chain" behaviour: it
would happily accept any garbage^Wuntrusted certificate chain without
notice -- when I'm not using "--x509cafile FOO" on the command line.
This isn't documented anywhere (manual, manpage, --help), I found this
out through systematic testing.

I find this most disturbing, since if I don't provide a set of trusted
X.509 CA certs, I trust nobody (rather than everybody as gnutls-cli
does)... gnutls-cli should bail out if it has no trusted root
certificates, rather than silently trust everyone. Go figure - there's a
difference between giving "--x509cafile /dev/null" and not giving this
option at all. :-(

While I'm at it, from the end user's perspective, I find it very hard to
figure what options I need for a proper configuration that doesn't use
b0rked protocols such as SSLv2, that uses proper X.509 certificate
validation to detect MITM attacks. Few applications except Firefox 3 get
that right, and I couldn't tell one off-hand.

I think that EVERY tool that has a remotely security-related context
should default to bulletproof mode and require that the user relaxes
every test explicitly.

Yes, I need to do homework here, fetchmail doesn't get this right
either... compatibility and all that.

So I'd say make Gnus default to gnutls-cli and change the sample
configuration to include --x509cafile and add instructions to the
defcustom blah self-documentation telling the user to cat(1) his trusted
ROOT certificates (in PEM format) together to form this file.

-- 
Matthias Andree