On Saturday, 17 September 2016 20:09:40 CEST David Benjamin wrote: > Hi folks, > > We've run into some problems with client certificate alerts in Chrome that > I'd like to fix going forward. > > The first is easy. handshake_failure is an unhelpful alert for server which > required client certs. This confuses users, so we're planning to > heuristically map it to a client certificate error if it's received after > declining to send certs. This seems poor, so I've uploaded this PR which > adds a certificate_required alert: > https://github.com/tlswg/tls13-spec/pull/640
+1 > Second, there is the access_denied alert. This alert has an unfortunate > name. Per spec, it is for: > > access_denied > A valid certificate [TLS1.3: or PSK] was received, but when access > control was > applied, the sender decided not to proceed with negotiation. This > message is always fatal. > > Accordingly, Chrome maps it to a client certificate error. But, by the name > alone, it sounds much more general. We're seeing evidence of some kind of > network filtering software mistakenly sending it to block a connection. (I > can't blame them too much, since we ourselves mistook it for an alert to > send in a server-side DoS handler! This has since been fixed.) > > From an unscientific survey of recent Chrome user complaints about this > error, this is twice as prominent as actual client cert errors! So we'll > want to add another heuristic: if we see access_denied without a > CertificateRequest, map it to a more generic TLS error. This also seems > worth fixing going forward. > > Does anyone actually send this alert? OpenSSL does not appear to. I've done a quick survey of about 60 servers, given the different intolerancies and limits they appear to have. Just that 60 servers were handled by at least a dozen different implementations, 2 of which were unique and unless people already deployed 1.1.0 in droves, the dominant implementation didn't look like OpenSSL. So I don't think we should guide ourselves with what OpenSSL does or doesn't do. > My best > rename is certificate_denied if we drop 1.3's "or PSK", but perhaps we can > remove the alert completely? You haven't gotten application data yet, so > you don't really have anything to apply access control on, particularly for > PSK. (For certs, there's post-handshake auth, but I would think you'd send > an application-level error there?) if it was already misused by multiple people, deprecating it and creating a new one probably is a good idea to make it unambiguous. -- Regards, Hubert Kario Senior Quality Engineer, QE BaseOS Security team Web: www.cz.redhat.com Red Hat Czech s.r.o., Purkyňova 99/71, 612 45, Brno, Czech Republic
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