hostname matching

Posted Jun 8, 2017 7:33 UTC (Thu) by njs (subscriber, #40338)
In reply to: hostname matching by tialaramex
Parent article: Python ssl module update

I was going to say oh it's not that bad, but it turns out that was based on a misreading of the source... it's not just that they have the wrong IDNA standard implemented :-(. In fact Python's SSL module's hostname verification will encode whatever hostname you gave it to a U-label (even if you forcibly pass in an A-label yourself), and then it will compare that against the raw subjectAltNames and CN. So currently the *only* situation in which the stdlib ssl module will successfully connect to a IDN over TLS is when the CN has the U-label in it.

In conclusion, TLS is hard and software is hard and everything is terrible.

hostname matching

Posted Jun 8, 2017 22:32 UTC (Thu) by tialaramex (subscriber, #21167) [Link] (1 responses)

While I appreciate that the "and everything is terrible" line seems appropriate here, might we at least raise this as a clear bug? Can I do that somewhere? Or if it already exists, can I be told where the bug report is so I can ensure it gets tended to by others who grok this stuff and will try to "gently" direct people towards actually doing what the spec. says ?

From the Web PKI side, bugs like this mean when we say to CAs "Don't do X" they point at the bug and say "We have to because of this bug". And so another year or six goes by without the problem fixed. Python being part of the problem not the solution is disappointing.

hostname matching

Posted Jun 11, 2017 8:26 UTC (Sun) by njs (subscriber, #40338) [Link]

The determinedly broken hostname matching is: https://bugs.python.org/issue28414
The lack of IDNA 2008 is: https://bugs.python.org/issue17305

I also just alerted Cory to the issue in the hopes that his new TLS library will hopefully avoid this problem... the Python ssl maintainer(s) is (are) certainly aware of it, but the stdlib ssl module is (like everything) pretty under-resourced, and with the Python release cycle and the py2/py3 split getting this kind of complex change done can be really slow :-/