Re: [alto] Eric Rescorla's Discuss on draft-ietf-alto-xdom-disc-04: (with DISCUSS and COMMENT)

["Mirja Kuehlewind (IETF)" <[e-mail]>]

Hi Sebastian,

thanks! I think that’s the right thing to do. Can you check with Benjamin and Ekr if that is a way forward (eventually starting a new thread with both of them). If we can’t come to a conclusion (soonish), I can schedule that as a discussion on an informal telechat.

Mirja

 

> Am 28.01.2019 um 00:09 schrieb Sebastian Kiesel <[e-mail]>:
> 
> Hi Mirja, all,
> 
> On Fri, Jan 18, 2019 at 11:12:32AM +0100, Mirja Kuehlewind (IETF) wrote:
>> Hi Sebastian,
>> 
>> so to summarize I think what’s needed is some discussion about what
>> can happen if DNSSEC is not used and maybe even a requirement that
>> certain data MUST be integrity protected.
>> 
>> I think that could also address Benjamin’s discuss. Can you maybe
>> propose some new/additional text for the security consideration
>> section and see if we can first address Ekr discuss and then start a
>> conversation with Benjamin?
> 
> I think the discussion about what could happen without DNSSEC was
> already pretty accurate, but I've reworked it a bit, see below.
> 
> The authenticity of the whole scheme indeed relies completely on DNSSEC.
> So the real question is, which level of requiring DNSSEC is apropriate
> and will address both Discusses.  My proposal is:
> 
>    All implementations of the cross-
>    domain ALTO server discovery procedure MUST support DNSSEC or be
>    able to use of such functionality in the underlying operating
>    system.  Network operators that publish U-NAPTR resource records
>    to be used for the cross-domain ALTO server discovery procedure
>    SHOULD use DNSSEC to protect their subdomains of in-addr.arpa.
>    and/or ip6.arpa., respectively.
> 
> 
> What do you think?
> 
> Thanks
> Sebastian
> 
> 
> ----- Begin proposal for new section 6.1 -----
> 
> 6.1.  Integrity of the ALTO Server's URI
> 
>   Scenario Description
>      An attacker could compromise the ALTO server discovery procedure
>      or the underlying infrastructure in a way that ALTO clients would
>      discover a "wrong" ALTO server URI.
> 
>   Threat Discussion
>      The cross-domain ALTO server discovery procedure relies on a
>      series of DNS lookups, in order to produce one or more URI(s).  If
>      an attacker was able to modify or spoof any of the DNS records,
>      the resulting URI(s) could be replaced by forged URI(s).  This is
>      probably the most serious security concern related to ALTO server
>      discovery.  The discovered "wrong" ALTO server might not be able
>      to give guidance to a given ALTO client at all, or it might give
>      suboptimal or forged information.  In the latter case, an attacker
>      could try to use ALTO to affect the traffic distribution in the
>      network or the performance of applications (see also Section 15.1.
>      of [RFC7285]).  Furthermore, a hostile ALTO server could threaten
>      user privacy (see also Section 5.2.1, case (5a) in [RFC6708]).
> 
>   Protection Strategies and Mechanisms
>      The application of DNS security (DNSSEC) [RFC4033] provides a
>      means to detect and avert attacks that rely on modification of the
>      DNS records while in transit.  All implementations of the cross-
>      domain ALTO server discovery procedure MUST support DNSSEC or be
>      able to use of such functionality in the underlying operating
>      system.  Network operators that publish U-NAPTR resource records
>      to be used for the cross-domain ALTO server discovery procedure
>      SHOULD use DNSSEC to protect their subdomains of in-addr.arpa.
>      and/or ip6.arpa., respectively.  Additional operational
>      precautions for safely operating the DNS infrastructure are
>      required in order to ensure that name servers do not sign forged
>      (or otherwise "wrong") resource records.  Security considerations
>      specific to U-NAPTR are described in more detail in [RFC4848].
> 
>      In addition to active protection mechanisms, users and network
>      operators can monitor application performance and network traffic
>      patterns for poor performance or abnormalities.  If it turns out
>      that relying on the guidance of a specific ALTO server does not
>      result in better-than-random results, the usage of the ALTO server
>      may be discontinued (see also Section 15.2 of [RFC7285]).
> 
>   Note
>      The cross-domain ALTO server discovery procedure finishes
>      successfully when it has discovered one or more URI(s).  Once an
>      ALTO server's URI has been discovered and the communication
>      between the ALTO client and the ALTO server starts, the security
>      threats and protection mechanisms discussed in the ALTO protocol
>      specification [RFC7285] apply.
> 
>      A threat related to the one considered above is the impersonation
>      of an ALTO server after its correct URI has been discovered.  This
>      threat and protection strategies are discussed in Section 15.1 of
>      [RFC7285].  The ALTO protocol's primary mechanism for protecting
>      integrity (and confidentiality) is the use of HTTPS-based
>      transport, i.e., HTTP over TLS [RFC2818].  Typically, when the
>      URI's host component is a host name, a further DNS lookup is
>      needed to map it to an IP address, before the communication with
>      the server can begin.  This last DNS lookup (for A or AAAA
>      resource records) does not necessarily have to be protected by
>      DNSSEC, as the server identity checks specified in [RFC2818] are
>      able to detect DNS spoofing or similar attacks, after the
>      connection to the (possibly wrong) host has been established.
>      However, this validation based on the server certificate can only
>      protect the steps that occur after the server URI has been
>      discovered.  It cannot detect attacks against the authenticity of
>      the U-NAPTR lookups needed for the cross-domain ALTO server
>      discovery procedure, and therefore, these resource records have to
>      be secured using DNSSEC.
> 
> ----- End proposal for new section 6.1 -----
> 
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