The mailing list for users of the eduroam Configuration Assistant Tool (CAT)

[Stefan Winter <stefan.winter AT restena.lu>]

Hello,

> I would like to report a problem with the installer for Ubuntu.
> 
> Ubuntu Linux fails to verify the authentication server's certificate.
> Because it is altsubject, not CN that is validated.

Yes, it validates the subjectAltName:DNS, not the CN. That is intentional.

> This not only an issue if the certificate does not have altsubject.

You meant to write "This *is* only an issue ..."?

That would be true.

> The problem is that when /etc/NetworkManager/system-connections/eduroam
> is generated this line is added:
> 
> altsubject-matches=DNS:wifi.aau.dk;
> 
> It should have been:
> 
> domain_match=wifi.aau.dk
> 
> However the version of wpa_supplicant that comes with Ubuntu does not
> support that, and will ignore the line.

Well if your Linux distribution does not support that parameter, then it
is actually good that our installers don't try to set it, right?

You may want to file a bug report to Ubuntu to include a new version of
wpa_supplicant this new parameter recognised (at least
wpa_supplicant-2.8 supports it). You would also need to lobby
NetworkManager folks to create a new API method for it. The most recent
version supports domain-suffix-match but not domain-match
(https://developer.gnome.org/NetworkManager/stable/settings-802-1x.html)
[alternatively, one could settle for using domain-suffix-match]

Only when that supporting lower-layer infrastructure is available, our
installers can make use of that.

There is a reason why eduroam has a page with EAP server certificate
recommendations. They state that for maxmimum compatibility,
certificates should have CN and at least one sAN:DNS and that the value
in CN should also also be one of those sAN:DNS values.

We don't recommend this only for Linux reasons. The EAP method
specifications are not at all clear which field has precedence over
which other, and which need to be present. So the safest thing to do is
to make sure that the correct string is present in both variants.

Don't get me wrong: I do see that domain_match is superior to
altsubject_match because it provides a fallback. And both of these two
are superior to the subject_match we were forced to use years ago when
nothing else was available.

But we can't move on to this newest and more compatible way of
configuring unless all the distributions we care about actually ship
with code supporting it.

And until then I'm afraid the solution is to have a certificate with a
CN=subjectAltName.DNS .

Greetings,

Stefan Winter

> You can see below why I came to this conclusion:
> 
> 
> Ubuntu 19.04
> ------------
> When I fist run the installation I get this error in my FreeRadius log:
> 
> Login incorrect (eap_peap: TLS Alert read:fatal:internal error)
> 
> It then works if I in Ubuntu go to "Wi-Fi > Visible networks > eduroam",
> change nothing, and click apply.
> 
> After further investigation I found that 4 lines get removed from
> /etc/NetworkManager/system-connections/eduroam.nmconnection when I click
> apply.
> 
> The line that caused the problem was altsubject-matches=DNS:wifi.aau.dk;
> 
> The CN of the radius server certificate is wifi.aau.dk. Both iOS, MacOS
> and Windows performs this check without problems.
> 
> 
> Ubuntu 18.04
> ------------
> Radius log is slightly different:
> 
> Login incorrect (eap_peap: TLS Alert read:fatal:certificate unknown)
> 
> Context of syslog
> TLS: altSubjectName match 'DNS:wifi.aau.dk' not found
> wlp2s0: CTRL-EVENT-EAP-TLS-CERT-ERROR reason=6 depth=0
> subject='/C=DK/ST=Denmark/O=Aalborg Universitet/OU=IT
> Services/CN=wifi.aau.dk' err='AltSubject mismatch'
> 


-- 
Stefan WINTER
Ingenieur de Recherche
Fondation RESTENA - Réseau Téléinformatique de l'Education Nationale et
de la Recherche
2, avenue de l'Université
L-4365 Esch-sur-Alzette

Tel: +352 424409 1
Fax: +352 422473

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