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Author DK26
Recipients DK26, christian.heimes
Date 2019-08-14.15:47:24
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Message-id <>
In-reply-to <>

I see your point :)

Modification of the original certificiation is legally problematic.

Much thanks for the patience and time to explain,

On Wed, Aug 14, 2019, 17:23 Christian Heimes <> wrote:

> Christian Heimes <> added the comment:
> On 14/08/2019 15.37, David K. wrote:
> >
> > David K. <> added the comment:
> >
> > Hi,
> >
> > Judging by your comment, I think there is a an unfortnate
> misunderstanding.
> >
> > If you'd be kind enough, please let me explain:
> >
> > 1. The issue I had was indeed on Python 3.7, using the highly used
> > "requests" library. Also my change was -not- applied on the deprecated
> > ssl.match_hostname()
> > but on _dnsname_match() which is a method of another inner class.
> > My point is that it's still releveant.
> Except it's not revelant any more because that function is no longer
> used by CPython's ssl module. Neither match_hostname nor any of its
> helper functions are called by code in the ssl module. Since 3.7 all
> hostname verification is now performed by OpenSSL code directly.
> ssl.match_hostname will be removed in 3.9 or 3.10.
> Latest urllib3 and requests don't use ssl.match_hostname() either. The
> urllib3 package has an older copy of the hostname matching algorithm in
> urllib3.packages.ssl_match_hostname. It should not be used with modern
> Python.
> > 2. Although there is a thin line here, it is not a configuration issue by
> > its classic meaning. It's an outside condition in a production
> environment
> > that unpatches Python code cannot handle and thus implicating that Python
> > is less stable and mistake tolerant than C# and Java (those are the other
> > more used languages in the company which weren't effected by this problem
> > -- for some who wouldn't bother like me to patch python source code, this
> > could be a deal breaker to move to another language).
> Your setup has a misconfigured X.509 certificate with a SAN entry that
> violates standards for certificates. You are asking me to introduce a
> security into Python as a workaround for the misconfiguration.
> The algorithm in match_hostname() and _dnsname_match() implements RFC
> 6125, section 6.4.3, in a strict way. Python not only refuses to match
> invalid wildcard entries, it also fails hard on RFC 6125 violations.
> > 3. It's a very simple fix that only removes white spaces (empty chars)
> from
> > start and end of the DNS before applying all the other tests on it. In
> fact
> > by assuring the input of the DNS name, our code becomes -more- secure. In
> > current state, a missed type DNS name encoded in the certifications could
> > cause unknowingly Python deamons to stop transmiting data. Also as humans
> > tend to make such naive errors, a mallicious party could make an attack
> be
> > seemless and  be discarded as human error. And if that doesn't convince
> > you, we can say at the very least the service we provide with our App
> > becomes unusable and unavailable to clients and for some that could cost
> > time and money and Python may take the blame as unreliable as compared to
> > other languages.
> You view the fix as simple and harmless. I see it as a violation of
> standards and a security bug. X.509 certs are complex and fragile
> beasts. Python have had several CVEs in the hostname matching code
> because we didn't implement it correctly. Certificates are also used in
> legal contracts, e.g. to legally sign documents or establish mutual
> trust. You cannot just modify the content of a certificate.
> Since you are worried about the reliability of Python and started
> talking about money, have you considered to donate money to the PSF?
> Python is maintained by unpaid volunteers. Donations to the Python
> Software Foundation help. (Disclaimer: No money in the world will change
> my opinion about "dn.strip()".)
> > 4. The thrown exception can be misleading: The exception says that the
> > problem is a partial wildcard. However the problem is white spaces which
> > can be difficult to spot. White spaces cannot be part of DNS names thus
> it
> > makes no sense to ackonwledge them or refer to them or event test them as
> > any other legit legal char. Also this is unpredictible to the programmer
> as
> > he wouldn't think such a basic trim/strip of white spaces wouldn't happen
> > in the core of the SSL code what's worse, it can't be handled conventialy
> > with catching the exception. While a programmer can edit Python source
> code
> > to it's needs,  they really shouldn't mess with it for more than a short
> > term use. Declining the change dooms me for example to always add this
> > change to projects using SSL.
> The problem is not the code but the certificate. If you don't care about
> valid certificate, then maybe disable hostname / certificate
> verification. Or role your own verification. There is no need to modify
> any source code for that.
> ----------
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Date User Action Args
2019-08-14 15:47:25DK26setrecipients: + DK26, christian.heimes
2019-08-14 15:47:25DK26linkissue37845 messages
2019-08-14 15:47:24DK26create