OpenSSL::SSL ignores DN if subjectAltName is specified
In ext/openssl/lib/openssl/ssl.rb, verify_certificate_identity seems to intentionally not check the DN if any subjectAltName extensions are found.
The subject alternative names extension allows additional identities
to be bound to the subject of the certificate. ...
which suggests that it contains additional identities, and thus does not exclude the subject.
This functionality was added way back in 2005, r7970:
* ext/openssl/lib/openssl/ssl.rb (OpenSSL::SSL::SSLSocket#post_connection_check): new method.
and moved around several times since then.
#2 [ruby-core:45228] Updated by MartinBosslet (Martin Bosslet) over 5 years ago
- Status changed from Assigned to Feedback
- Priority changed from Normal to 3
RFC 3280 was obsoleted by 5280 and there, the wording is slightly different:
188.8.131.52. Subject Alternative Name
The subject alternative name extension allows identities to be bound
to the subject of the certificate. These identities may be included
in addition to or in place of the identity in the subject field of
But I think we should orient ourselves at RFC 6125 , which
explicitly addresses how to do hostname verification for TLS services.
There, it says:
6.4.4. Checking of Common Names
As noted, a client MUST NOT seek a match for a reference identifier
of CN-ID if the presented identifiers include a DNS-ID, SRV-ID,
URI-ID, or any application-specific identifier types supported by the
Therefore current behavior is in line with this and correct in doing so.
But what's missing is verification of the service type parts and
interpretation of the otherName attributes of type srvName (RFC4985), I
could imagine adding support in the future, especially if CAs start to
follow these recommendations.
But I'll mark this as low prio for now if nobody objects.