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Re: python-urllib3 1.25.6 uploaded to experimental (closes CVE-2019-11236) but fails build tests

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On Sun, Oct 13, 2019 at 10:31:31PM +0800, Drew Parsons wrote:
> It conditionally works.  Using curl, I found that TLSv1_0 or TLSv1_1 will
> support a successful connection, but only if the maximum SSL_VERSION is
> constrained to TLSv1_0 or TLSv1_1 (e.g. curl -v --tlsv1.1 --tls-max 1.1
> https://pub.orcid.org). Without the max, the connection fails:
> $ curl --tlsv1.1  https://pub.orcid.org
> curl: (35) error:14094410:SSL routines:ssl3_read_bytes:sslv3 alert handshake
> failure
> 
> The urllib3 failure was similar, but I do not know how to set tls-max with
> urllib3. I could only find the option with curl.  I could set up a custom
> HTTPAdapter as suggested at https://requests.readthedocs.io/en/master/user/advanced/#example-specific-ssl-version
> to set ssl_version=ssl.PROTOCOL_TLSv1_1 but the ssl module doesn't have the
> SSLVERSION_MAX_TLSv1_1 value that curl has. I could solve it with pycurl
> using c.setopt(pycurl.SSLVERSION, pycurl.SSLVERSION_TLSv1_1 |
> pycurl.SSLVERSION_MAX_TLSv1_1)

For sure I'm missing something, but why not just set TLS version?
I tried the following on both Python2 and Python3:

    >>> import ssl
    >>> from urllib3.poolmanager import PoolManager
    >>> http = PoolManager(ssl_version=ssl.PROTOCOL_TLSv1)
    >>> r = http.request('GET', 'https://pub.orcid.org')
    >>> r.status
    200


> Evidently the orcid server only supports TLSv1.0 and TLSv1.1 and no higher
> (why haven't they activated TLSv1.3 yet?!), while curl and urllib3 without
> tls-max first test TLSv1.3 and then quit without cascading downwards once
> they receive the TLSv1.3 handshake failure.  Which is rather odd behaviour
> when I think about it.  The whole point of supporting multiple protocol
> versions is to try the next available version if the first one doesn't work.

Not an expert here, but I think fallback is not done on purpose due downgrade
attacks: https://en.wikipedia.org/wiki/Downgrade_attack

> I had a closer look.  The failing tests were in python2 only, coming from
> the non-ascii (Gërman http://Königsgäßchen.de/straße and Japanese
> http://ヒ:キ@ヒ.abc.ニ/ヒ?キ#ワ) unicode url tests. So from one perspective
> we don't need to worry so much about them, we could just disable them (e.g.
> prepend @onlyPy3 to test_parse_url and test_url_vulnerabilities in
> test_util.py). We'll be dropping python2 any way in the near future.
> 
> On the other hand, given the nature of the vulnerabilities and the possible
> uses of urllib3, it's probably best not to leave python2 untested,
> especially since they are known to pass on python2 anyway in the right
> conditions.  Probably there is some package that should be added to
> Build-Depends to enable python2 tests to pass, though I have no idea which
> that package might be.

Fixed adding python{,3}-idna on B-D. I had to add python3-idna
because the same tests were failing also on Python3 when I tested
them buinding on DoM.

Kind regards,

-- 
  Daniele Tricoli 'eriol'
  https://mornie.org

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Re: python-urllib3 1.25.6 uploaded to experimental (closes  CVE-2019-11236) but fails build tests Drew Parsons <dparsons@debian.org> - 2019-10-13 16:40 +0200
  Re: python-urllib3 1.25.6 uploaded to experimental (closes  CVE-2019-11236) but fails build tests Daniele Tricoli <eriol@debian.org> - 2019-10-27 16:30 +0100
    Re: python-urllib3 1.25.6 uploaded to experimental (closes  CVE-2019-11236) but fails build tests Drew Parsons <dparsons@debian.org> - 2019-10-27 17:30 +0100
      Re: python-urllib3 1.25.6 uploaded to experimental (closes  CVE-2019-11236) but fails build tests Michael Kesper <mkesper@schokokeks.org> - 2019-10-29 13:30 +0100
        Re: python-urllib3 1.25.6 uploaded to experimental (closes  CVE-2019-11236) but fails build tests Ondrej Novy <novy@ondrej.org> - 2019-10-29 14:20 +0100
        Re: python-urllib3 1.25.6 uploaded to experimental (closes  CVE-2019-11236) but fails build tests Jeremy Stanley <fungi@yuggoth.org> - 2019-10-29 14:40 +0100
          Re: python-urllib3 1.25.6 uploaded to experimental (closes  CVE-2019-11236) but fails build tests Michael Kesper <mkesper@schokokeks.org> - 2019-10-29 15:40 +0100

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