[erlang-questions] Wildcard certificate rejected with hostname_check_failed

Ingela Andin ingela.andin@REDACTED
Tue Oct 8 18:53:28 CEST 2019

You need to use the ssl option:


to allow wildcard certs!

Regards Ingela Erlang/OTP team - Ericsson AB

Den tors 3 okt. 2019 kl 00:22 skrev Dániel Szoboszlay <dszoboszlay@REDACTED

> Hi,
> I'm trying to connect to the server foobar.example.com with ss from an
> Erlang node. The server presents a wildcard certificate with an
> ?'id-ce-subjectAltName' extension that looks like this:
> {'Extension', {2,5,29,17}, false,
>  [{dNSName, "*.example.com"},
>   {dNSName, "example.com"}
>  ]}
> The peer verification (default one) fails with hostname_check_failed. I
> traced the problem back to public_key:verify_hostname_match_default0/2
> which gets called like this:
> public_key:verify_hostname_match_default0(
>   {dns_id, "foobar.example.com"},
>   {dNSName, "*.example.com"})
> This check fails. The function has one clause for matching a dns_id
> against a dNSName, and it requires an exact match. It also has a clause
> that allows wildcards, but that's only for matching a (non-wrapped) fqdn
> against a cn tuple:
> https://github.com/erlang/otp/blob/5bf0a8a2a18a8e883792692bdc060e37552b0d08/lib/public_key/src/public_key.erl#L1672-L1675
> Why isn't the wildcard matching enabled for the dns_id against dNSName case
> too? The fqdn against cn scenario is only used as a fallback when the
> certificate doesn't contain an ?'id-ce-subjectAltName' extension. But as
> far as I can tell wildcard certificates typically have the extension,
> instead of (or besides) using a wildcard in the CN (see for example the
> certificate presented by https://blog.hu/).
> The public_key User's Guide
> <http://erlang.org/doc/apps/public_key/using_public_key.html#the-verification-process>
>  says:
> In case where the Presented IDs are fetched from the Subject certificate
>> field, the names may contain wildcard characters. The function handles this
>> as defined in chapter 6.4.3 in RFC 6125
>> <https://tools.ietf.org/html/rfc6125#section-6.4.3>.
> But as I understand, chapter 6.4.3 speaks about presented ids *in general*.
> Where does this restriction to the subject field come from?
> Thanks,
> Daniel
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