(ITS#5938) tls.c does not conform to RFC 4513

[nick.hudson@isode.com]

Full_Name: nick hudson
Version: 2.3.38
OS: linux
URL: 
Submission from: (NULL) (62.3.217.250)


I am looking at the code in tls.c, function ldap_pvt_tls_check_hostname
(although the code has been refactored in recent versions, into e.g. tls_o.c,
but the same is true of the new code)

I think the code is doing something that RFC 4513 says that it should not do. 
Specifically, ref RFC 4513 section 3.1.3 says:

   The server's identity may also be verified by comparing the reference
   identity to the Common Name (CN) [RFC4519] value in the leaf Relative
   Distinguished Name (RDN) of the subjectName field of the server's
   certificate.  This comparison is performed using the rules for
   comparison of DNS names in Section 3.1.3.1, below, with the exception
   that no wildcard matching is allowed. 

In tls.c (and the refactored code), you can see it's first attempting an exact
comparison on subjectAltName, and if that fails it tries a wildcard match (which
is ok, as per section 3.1.3.1)

But if no subjectAltName match is found, there's another section which looks at
the certificate's subjectname, in which it also does a wildcard match, although
the RFC says this shouldn't be done.