Re: [secdir] secdir Review of draft-ietf-pcp-nat64-prefix64-04

<mohamed.boucadair@orange.com> Fri, 24 January 2014 12:51 UTC

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From: <mohamed.boucadair@orange.com>
To: Stephen Hanna <shanna@juniper.net>, "secdir@ietf.org" <secdir@ietf.org>, The IESG <iesg@ietf.org>, "draft-ietf-pcp-nat64-prefix64.all@tools.ietf.org" <draft-ietf-pcp-nat64-prefix64.all@tools.ietf.org>
Date: Fri, 24 Jan 2014 13:51:00 +0100
Thread-Topic: secdir Review of draft-ietf-pcp-nat64-prefix64-04
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Subject: Re: [secdir] secdir Review of draft-ietf-pcp-nat64-prefix64-04
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Re-,

For issue#9, I didn't added any change for the moment but will reconsider it if we received a similar comment during the WGLC. 

The next revision of the draft will include what we have agreed so far.

Thank you very much for your careful review. Much appreciated !

Cheers,
Med

>-----Message d'origine-----
>De : Stephen Hanna [mailto:shanna@juniper.net]
>Envoyé : vendredi 24 janvier 2014 11:54
>À : BOUCADAIR Mohamed IMT/OLN; secdir@ietf.org; The IESG; draft-ietf-pcp-
>nat64-prefix64.all@tools.ietf.org
>Objet : RE: secdir Review of draft-ietf-pcp-nat64-prefix64-04
>
>Med,
>
>Thanks for addressing so many of my concerns. I'm happy with
>the changes that you have made.
>
>I didn't see a response to issue 9) below (about RFC 7050).
>Do you have any plans to address that?
>
>Thanks,
>
>Steve
>
>> -----Original Message-----
>> From: mohamed.boucadair@orange.com
>> [mailto:mohamed.boucadair@orange.com]
>> Sent: Friday, January 24, 2014 3:56 AM
>> To: Stephen Hanna; secdir@ietf.org; The IESG; draft-ietf-pcp-nat64-
>> prefix64.all@tools.ietf.org
>> Subject: RE: secdir Review of draft-ietf-pcp-nat64-prefix64-04
>>
>> Dear Stephen,
>>
>> Please see inline.
>>
>> Cheers,
>> Med
>>
>> >-----Message d'origine-----
>> >De : Stephen Hanna [mailto:shanna@juniper.net]
>> >Envoyé : jeudi 23 janvier 2014 16:20
>> >À : BOUCADAIR Mohamed IMT/OLN; secdir@ietf.org; The IESG; draft-ietf-
>> pcp-
>> >nat64-prefix64.all@tools.ietf.org
>> >Objet : RE: secdir Review of draft-ietf-pcp-nat64-prefix64-04
>> >
>> >Med,
>> >
>> >Thanks for your response. Coming along nicely!
>> >
>> >A few comments on your changes below, marked with [SRH].
>> >
>> >Thanks,
>> >
>> >Steve
>> >
>> >Med wrote:
>> >> Steve wrote:
>> >> >1) The second paragraph of the Security Considerations section
>> >> >   points out that if an attacker can fool a host into using
>> >> >   the wrong value for Pref64::/n, the traffic generated using
>> >> >   that value will be delivered to the wrong location. That's
>> >> >   right but not all the implications are mentioned. A MITM
>> >> >   (Man In The Middle) attack can be performed in this manner,
>> >> >   permitting alterations to the traffic (not just eavesdropping).
>> >> >   This should be mentioned.
>> >> [Med] I updated the text as follows:
>> >>
>> >> OLD:
>> >>
>> >>    As discussed in [RFC6147], if an attacker can manage to change
>> the
>> >>    Pref64::/n used by the DNS64 function, the traffic generated by
>> the
>> >>    host that receives the synthetic reply will be delivered to the
>> >>    altered Pref64.  This can result in either a denial-of-service
>> (DoS)
>> >>    attack, a flooding attack, or an eavesdropping attack.  This
>> attack
>> >>    could be achieved either by altering PCP messages issued by a
>> >>    legitimate PCP server or by using a fake PCP server.
>> >>
>> >> NEW:
>> >>
>> >>    As discussed in [RFC6147], if an attacker can manage to change
>> the
>> >>    Pref64::/n used by the DNS64 function, the traffic generated by
>> the
>> >>    host that receives the synthetic reply will be delivered to the
>> >>    altered Pref64.  This can result in either a denial-of-service
>> (DoS)
>> >>    attack, a flooding attack, or a MIM (Man In The Middle) attack.
>> >> This attack
>> >>    could be achieved either by altering PCP messages issued by a
>> >>    legitimate PCP server or by using a fake PCP server.
>> >>
>> >> Better?
>> >
>> >[SRH] Yes, but the conventional abbreviation for
>> >Man In The Middle is MITM not MIM. Who knows why?!
>> [Med] Fixed.
>>
>> >
>> >> >2) The next paragraph of the Security Considerations section
>> >> >   suggests defenses to prevent the attacker from substituting
>> >> >   the wrong value for Pref64::/n. However, the defense that
>> >> >   is suggested (IP-based ACLs on the PCP server, client, or
>> >> >   network) won't help much. Attackers can just place the
>> >> >   PCP server's IP address in the source address of the fake
>> >> >   PCP response packet sent by the attack.
>> >>
>> >> [Med] anti-spoofing filters can be used to prevent such attack.
>> Ingress
>> >> filters can be also enforced at boundaries of a domain to prevent
>> such
>> >> attack. I do think the text is still correct.
>> >
>> >[SRH] These countermeasures provide no defense against an attacker
>> >who is on the path from the PCP server to the client. This is
>> >not a theoretical attack, as described in certain news reports
>> >recently (Der Spiegel).
>> [Med] The deployment I have in mind is a pcp service offered by a
>> service provider while pcp clients are hosted in a CPE or in connected
>> devices (either behind the CPE or directly to the service provider
>> network). To achieve the attack vector you described, the mis-behaving
>> node should be in the service provider network or connected to that
>> network. If that service provider enforced anti-spoofing filters, then
>> a mis-behaving node cannot act as a fake pcp server.
>>
>> I understand this is a deployment case among others. So to be accurate,
>> I changed the text as follows:
>>
>> OLD:
>>    For example, access control lists (ACLs) can be installed on the PCP
>>    client, PCP server, and the network between them, so those ACLs
>> allow
>>    only communications from a trusted PCP server to the PCP client.
>>
>> NEW:
>>    In some deployments, access control lists (ACLs) can be installed on
>>    the PCP client, PCP server, and the network between them, so those
>>    ACLs allow only communications from a trusted PCP server to the PCP
>>    client.
>>
>>
>> >
>> >> > The nonce in the
>> >> >   MAP or PEER response means that the attacker must capture
>> >> >   or predict this value but no nonce is present in the ANNOUNCE
>> >> >   response so that would probably be the preferred attack
>> >> >   method, especially since ANNOUNCE responses can be sent
>> >> >   out via multicast at any time. I suggest that the spec
>> >> >   prohibit sending the PREFIX64 option in a multicast
>> >> >   ANNOUNCE response, unless effective countermeasures for
>> >> >   this attack are found.
>> >> [Med] Isn't this covered by this text:
>> >>
>> >> "   Means to defend against attackers who can modify packets between
>> >> the
>> >>    PCP server and the PCP client, or who can inject spoofed packets
>> >> that
>> >>    appear to come from a legitimate PCP server SHOULD be enabled."
>> >
>> >[SRH] That would be a reasonable countermeasure if such means
>> >actually existed. Could you describe what those means
>> >would be? As I mentioned above, ingress filters and
>> >anti-spoofing filters are ineffective against on-path
>> >attackers.
>> [Med] As mentioned above, ACLs are sufficient in some deployment
>> contexts.
>>
>>
>> >
>> >> >In addition to these security issues, I found some other issues
>> >> >that are not related to security:
>> >> >
>> >> >1) You should explain that RFC 6146 defines Pref64::/n.
>> >> >   Otherwise, that term is quite cryptic.
>> >> [Med] I added this new sentence:
>> >>
>> >>    According to [RFC6146], NAT64 uses Pref64::/n to construct
>> >>    IPv4-Converted IPv6 addresses as defined in [RFC6052].
>> >>
>> >> Better?
>> >
>> >[SRH] Great!
>> >
>> >[SRH] Deleted several more comments that you have addressed.
>> >
>> >> >6) Text near the top of page 8 says "The PCP server can be
>> >> >   configured with a customized IPv6 prefix list" but that
>> >> >   won't work when PREFIX64 is added to a multicast ANNOUNCE
>> >> >   response. That's another reason not to permit this, in
>> >> >   addition to security issue 2) above.
>> >> [Med] I added this sentence:
>> >>
>> >> " Note, it is NOT
>> >>       RECOMMENDED to include PREFIX64 options in ANNOUNCE messages
>> if a
>> >>       customized IPv6 prefix list is configured to the PCP server. "
>> >>
>> >> Better?
>> >
>> >[SRH] Maybe. Is there some way that including PREFIX64 options in
>> >ANNOUNCE messages will work if a customized IPv6 prefix list
>> >is configured to the PCP server? If not, this should be a
>> >MUST NOT instead of a NOT RECOMMENDED.
>>
>> [Med] An example is the use of separate zones (see for instance
>> http://tools.ietf.org/search/draft-penno-pcp-zones-01) or if several
>> logical topologies are configured.
>>
>> >
>> >> >7) When IPv4 prefix lists are configured and multiple IPv6
>> >> >   prefix lists are also configured, the first PREFIX64
>> >> >   option includes the IPv4 prefix lists. Can the later
>> >> >   PREFIX64 options also include their own IPv4 prefix
>> >> >   lists? If one or more of those later PREFIX64 options
>> >> >   does NOT have its own IPv4 prefix list, what does that
>> >> >   mean? Does it inherit the IPv4 prefix list of the
>> >> >   previous PREFIX64 option? The current text is not clear.
>> >> [Med] Only the first occurrence can carry the IPv4 prefix because
>> other
>> >> occurrences are not used by building IPv4-converted addresses, but
>> only
>> >> to distinguish these addresses if received in referrals. I can add a
>> >> sentence to indicate this explicitly in the text.
>> >
>> >[SRH] Thanks. Please do.
>> [Med] I added this sentence to Section 4.1:
>>
>> " When multiple PREFIX64 options are included in the same PCP message,
>> only the first PREFIX64 option occurrence may include the IPv4 Prefix
>> List field."
>>
>>
>> >
>> >> >8) The example in section 5.1 says that it "depicts a
>> >> >   typical usage of the PREFIX64 option when a DNS64
>> >> >   capability is embedded in the host." Did you mean
>> >> >   "is not embedded"? I don't see how DNS64 is being
>> >> >   used in this example.
>> >>
>> >> [Med] The text is correct. DNS64 is used to form locally an IPv4-
>> >> converted IPv6 address. The example assumes the address of the IPv4
>> >> server is retrieved using A records. DNS exchanges are not mentioned
>> in
>> >> the figure to avoid overloading it.
>> >
>> >[SRH] OK. You may want to explain this a bit more.
>> [Med] I made this change:
>>
>> OLD:
>> "once the IPv6-only client discovers the IPv4 address of the remote
>> IPv4-only server"
>>
>> NEW:
>> " once the IPv6-only client discovers the IPv4 address of the remote
>> IPv4-only server (e.g., using DNS)"
>>
>> and added this sentence:
>>
>> " Note: DNS exchange to retrieve the IPv4 address of
>>       the IPv4-only Server is not shown in the figure. "
>>
>> >
>> >> >9) Is this document still relevant? RFC 7051 says:
>> >> >
>> >> >   Our conclusion is to recommend publishing the Well-Known DNS
>> Name
>> >> >   heuristic discovery-based method as a Standards Track IETF
>> document
>> >> >   for applications and host implementors to implement as-is.
>> >> >
>> >> >   With that, is there still a need for this document?
>> >> [Med] Yes, this is explicitly mentioned in the shepherded text of
>> >> RFC7050. Please refer to
>> >> https://datatracker.ietf.org/doc/rfc7050/history/
>> >>
>> >> "    The document specifies a heuristic that is not perfect and so
>> some
>> >>     points were rough, but the constraint for this document was to
>> >> operate
>> >>     without changes to code (only configuration) in existing
>> networks.
>> >>     Given that constraint, there was strong consensus.  Relaxing the
>> >>     constraint would allow one to do better, and that is the focus
>> of a
>> >>     draft recently submitted to the PCP WG."
>> >
>> >[SRH] OK, fine. You might want to mention that in your draft.
>> >Otherwise, other readers may have the same confusion. They're
>> >not likely to read the shepherd text for RFC 7050!
>> >
>>
>>
>