Re: SSL support in Ncat - client version issue: what do other apps do?

[David Fifield <david () bamsoftware com>]

On Wed, Feb 18, 2009 at 08:41:55AM +0100, Kristof Boeynaems wrote:
> On Wed, Feb 18, 2009 at 6:37 AM, David Fifield <david () bamsoftware com> wrote:
> > I looked at the source code of some other applications to see how they
> > handle SSL client connections. None that I found use the fallback/retry
> > technique that has been discussed (and implemented at
> > http://seclists.org/nmap-dev/2009/q1/0430.html).
> >
> > Wget only supports one client method at a time, but it provides
> > command-line options to choose which method to use. If you say
> > --secure-protocol=auto, it uses SSLv23_client_method, if you say
> > --secure-protocol=TLSv1, it uses TLSv1_client_method, etc. See
> > src/openssl.c.
> > http://www.gnu.org/software/wget/manual/html_node/HTTPS-_0028SSL_002fTLS_0029-Options.html
> >
> > cURL is the same, only supporting one method at a time but providing
> > options --tlsv1, --sslv2, --sslv3. If none of those are given the
> > SSLv23_client_method method is used. See lib/ssluse.c.
> >
> > socat again only supports one method per connection. It has a method
> > option to choose which one is used: method=SSLv2, method=SSLv23, etc.
> > See xio-openssl.c.
> > http://www.dest-unreach.org/socat/doc/socat.html#GROUP_OPENSSL
> >
> > That seems to be a common solution: provide SSL version selection for
> > use against those servers that require it, and use SSLv23_client_method
> > by default.
>
> Thanks for this list, very interesting!
>
> Accidentally I bumped into a post where Nessus discusses the exact
> same problem: http://list.nessus.org/pipermail/nessus-devel/2002-February/msg00002.html.
> Not sure how they currently implement it, but apparently in 2002, the
> plan was to try 4 different connections.

I looked at the source of libnessus 2.2.8 (downloaded with "apt-get
source libnessus-dev" as the Nessus site wanted me to click through some
agreement). I can't find where they try multiple connection. The only
file that mentions client methods is libnessus/network.c, and it appears
to use the same pattern of allowing one configurable method per
connection. I could be reading the code wrong, or maybe that code itself
is called multiple times. Here's an online copy of the file:
http://nessus-libraries.sourcearchive.com/documentation/2.2.10-3/network_8c-source.html
I was looking in the function open_SSL_connection.

I looked at OpenVAS but they have migrated everything over to GnuTLS.

The Debian changelog suggests that 1.0.10 would have been current at the
beginning of 2002. I found an SRPM for 1.0.9, but it contains no mention
of OpenSSL at all.

David Fifield

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