To avoid having to authenticate the LIS with a domain name that is different to"
the one used to identify it, a client MAY choose to reject URIs that
contain a domain name that is different to the U-NAPTR input. To
support endpoints that enforce the above restriction on URIs, network
administrators SHOULD ensure that the domain name in the DHCP option is
the same as the one contained in the resulting URI.
Isn't this overly restrictive? If this constraint were always to be enforced, why would we need U-NAPTR in the first place?
> From: acooper@cdt.org
> To: geopriv@ietf.org
> Date: Mon, 24 May 2010 18:24:33 +0100
> Subject: [Geopriv] Security considerations for LIS discovery
>
> [Sending on behalf of Richard whose email is down.]
>
> Hi all,
>
> In response to some feedback from the Security area during IESG
> review, the
> authors of draft-ietf-geopriv-lis-discovery have proposed a
> modification to
> the recommended authentication techniques. This email is soliciting
> feedback from the working group on whether there are any objections to
> the
> proposed change.
>
> Recall that a client discovers a LIS by getting a domain name from
> DHCP and
> finding a URI via a U-NAPTR lookup for that name. The question is: If
> that
> URI is HTTPS, what name should be checked against the name in the
> certificate, the name from DHCP or the domain name in the URI? Prior
> versions had recommended checking the name in the certificate against
> the
> name in the URI, i.e., the *output* of the U-NAPTR process. This
> recommendation is counter to the advice in RFC 3958.
>
> The authors' proposal is to change the document so that the
> recommendation
> is to check the authenticated name against the DHCP name (in accordance
> with RFC 3958), and to provide some guidance for clients and networks in
> how to make this process implementable with current libraries (many of
> which only check the name in the URI). Detailed text is below.
> If you have any comments on this proposal, please send them to the
> list no
> later than 09:00 US EST (GMT-4) on Thursday, 27 May 2010.
>
> Thanks,
> --Richard
>
> OLD:
> U-NAPTR is entirely dependent on its inputs. In falsifying a domain
> name, an attacker avoids any later protections, bypassing them entirely.
> To ensure that the access network domain name DHCP option can be relied
> upon, preventing DHCP messages from being modified or spoofed by
> attackers is necessary. Physical or link layer security are commonplace
> methods that can reduce the possibility of such an attack within an
> access network; alternatively, DHCP authentication [RFC3118] can provide
> a degree of protection against modification or spoofing.
>
> The domain name that is used to authenticated the LIS is the domain name
> in the URI that is the result of the U-NAPTR resolution. Therefore, if
> an attacker were able to modify or spoof any of the DNS records used in
> the DDDS resolution, this URI could be replaced by an invalid URI. The
> application of DNS security (DNSSEC) [RFC4033] provides a means to limit
> attacks that rely on modification of the DNS records used in U-NAPTR
> resolution. Security considerations specific to U-NAPTR are described
> in more detail in [RFC4848].
>
> An "https:" URI is authenticated using the method described in Section
> 3.1 of [RFC2818]. The domain name used for this authentication is the
> domain name in the URI resulting from U-NAPTR resolution, not the input
> domain name as in [RFC3958]. Using the domain name in the URI is more
> compatible with existing HTTP client software, which authenticate
> servers based on the domain name in the URI.
>
> NEW:
> The domain name that used to authenticate the LIS is the domain name
> input to the U-NAPTR process, not the output of that process [RFC3958],
> [RFC4848]. As a result, the results of DNS queries do not need
> integrity protection.
>
> An "https:" URI is authenticated using the method described in Section
> 3.1 of [RFC2818]. HTTP client implementations frequently do not provide
> a means to authenticate a based on a domain name other than the one
> indicated in the request URI, namely the U-NAPTR output. To avoid
> having to authenticate the LIS with a domain name that is different to
> the one used to identify it, a client MAY choose to reject URIs that
> contain a domain name that is different to the U-NAPTR input. To
> support endpoints that enforce the above restriction on URIs, network
> administrators SHOULD ensure that the domain name in the DHCP option is
> the same as the one contained in the resulting URI.
>
> Authentication of a LIS relies on the integrity of the domain name
> acquired from DHCP. An attacker that is able to falsify a domain name
> circumvents the protections provided. To ensure that the access network
> domain name DHCP option can be relied upon, preventing DHCP messages
> from being modified or spoofed by attackers is necessary. Physical or
> link layer security are commonplace methods that can reduce the
> possibility of such an attack within an access network. DHCP
> authentication [RFC3118] might also provide a degree of protection
> against modification or spoofing.
>
>
>
>
>
>
>
>
>
>
>
>
>
>
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