Re: [tcpm] Last Call: draft-ietf-tcpm-tcpsecure (Improving TCP's Robustness to Blind In-Window Attacks) to Proposed Standard

["Anantha Ramaiah (ananth)" <[e-mail]>]

Fernando,
    Thanks for you comments. Pl see responses inline :- 

> -----Original Message-----
> From: [e-mail] [mailto:[e-mail]] On 
> Behalf Of Fernando Gont
> Sent: Monday, April 13, 2009 2:25 PM
> To: [e-mail]
> Cc: [e-mail]
> Subject: Re: [tcpm] Last Call: draft-ietf-tcpm-tcpsecure 
> (Improving TCP's Robustness to Blind In-Window Attacks) to 
> Proposed Standard
> 
> Folks,
> 
> Some last call comments:
> 
> * The document never mentions the fact that this document is 
> IPR-encumbered. As far as I recall, much of the dicussion 
> within tcpm with respect to the level of requirements of this 
> document (MAY/SHOULD/MUST, etc.) had to do with this fact. I 
> believe the document should include a warning mentioning that 
> there's an IPR on the document, so that implementers can 
> consider this point in their decision of whether to implement 
> the described mechanisms or not.

I am confused what to do since this is being brought up very late in the
game. That said, there are *many* drafts/RFC's that have IPR on them in
the whole of ietf. Do all them explicitly state the IPR link ? I'll
leave it to the collective wisdom of the group and the chairs to offer
guidance on this matter.

> 
> * The document discusses blind attacks, and to some extent 
> assesses the difficulty in guessing the four-tuple that 
> identifies a TCP connection.
> However, it does not even mention port randomization, which 
> is probably the most simple and straightforward approach for 
> mitigating blind attacks against TCP. This was raised by me 

Well, the point is that source port randomization is something external
like Ipsec and nothing specfic to TCP. TCP will work with or without src
port randomization. Now the scope of this document is to improve
robustness to TCP esp. in cases where the TCP connection is not
protected by other means like TCP MD5 or TCP AO etc., Now this point is
very clear in the document. That said I have no issues putting a
reference to the port randomization in the document.  


> and other quite a few times in the tcpm wg list, pre and post 
> wglc, but this comment was never addressed. It's particularly 
> curious that port randomization is not mentioned when tsvwg 
> is working on it (draft-ietf-tsvwg-port-randomization).

Yes, you did raise this issue last time, but I did defer it to the WG
and did not receive any response, so I simply left it at that.

> 
> * Among the factors that determine how easy these attacks be 
> exploited is the window size. This document should provide, 
> at the very least, pointers with advice on what to do with 
> the tcp window. While quickly skimming through RFC 4953, it 

It does mentions about the window size relationship, For example in the
beginning sections of the document we briefly mention the window size
and the # of packets that is required to generate a successful attack. 

> seems it has some advice on the TCP window. We do offer a 
> lengthy discussion of this and other issues in 
> draft-gont-tcp-security and 
> http://www.cpni.gov.uk/Docs/tn-03-09-security-assessment-TCP.pdf
> 
> * Yet another factor is TCP ISN randomization. At the very 
> least, this document could/should a pointer to RFC 1948. We 
> do offer a lengthy discussion of this and other issues in 
> draft-gont-tcp-security and 
> http://www.cpni.gov.uk/Docs/tn-03-09-security-assessment-TCP.pdf

Why should it talk about ISN randomization since ISN randomization, is
somewhat orthogonal to the type of attack here, it is not even one of
the attack vector.

We could refer this, but the scope of the current document is about the
RST/SYN and Data attacks and mitigations, Since this document generally
refers RFC 4953 (which came after this document was written. BTW) I
think this should suffice, IMO.

> 
> * Just of the top of my head: Hadn't the BGP spec been 
> updated so that a well-known port was not required as the 
> *source* port?

Not that I am aware of, I can look it up.

> 
> * The counter-measure of for the SYN-based reset attack may 
> have missed a common heuristics for the handling of SYN 
> segments. See pages 86 and
> 87 of the UK CPNI paper on TCP security. FWIW, we argue that 
> the processing of SYN segments proposed in [Ramaiah et al, 
> 2008] should apply only for connections in any of the 
> synchronized states other than the TIME-WAIT state.

We just followed RFC 793 as the base and the changes are made w.r.t
that. TIME-WAIT may be an exception but doesn't RFC 793 already has that
language correct?

> 
> * When it comes to TCP-based blind-connection reset attacks, 
> there's a much more trivial -- yet not discussed before? -- 
> alternative. See Section 11.1.3 and Section 11.1.4 in 
> draft-gont-tcp-security and the CPNI paper 
> (http://www.cpni.gov.uk/Docs/tn-03-09-security-assessment-TCP.pdf).
> These variants should, at the very least, be mentioned and a 
> pointer provided to them as, at least in theory, are much 
> easier to exploit.

Those sounds like some new proposals (security and precedence) different
stacks would have taken different measures to address this issue.
Anyways this is something new and hence needs more discussion and
evaluation. Has these ideas been submitted in a draft to TCPM? (your
recent BCP document tcp-security, covers it ?)

> 
> * When it comes to the data injection attack, Michael 
> Zalewski sketched another attack vector which may be easier 
> to exploit. We discuss it in Section 16.2 of 
> draft-gont-tcp-security and the CPNI doc, along with advice. 
> IMO, this vector should be mentioned, too.

This again is an attack which relies on the IP functionality and not
TCP.  For example the DF bit can be turned on then there is no
fragmentation involved, in any case the current document is not intended
as a protection for on-path attackers and not a complete solution for
all kinds of off-path attacks (pl note the security considerations
section). Also FWIW, our stacks already randomize IPID. Anyways these
are clearly outside the scope of the current document, IMO.

> 
> Needless to say, I'm in favor of improving the robustness of 
> TCP and, IPRs-aside, I'm happy with the implementation of the 
> counter-measures described in the tcpsecure I-D (all three).

Thanks.

> 
> I'm also glad that this doc is getting close to publication. 
> Five years working on a document is quite a lot of time! 

Agreed. Esp when it has been running in the internet with multiple
vendors supporting these mitigations.


-Anantha
> (yes, it could have been worse, some might argue).

> 
> Thanks!
> 
> Kind regards,
> Fernando Gont
> 
> 
> 
> 
> The IESG wrote:
> > The IESG has received a request from the TCP Maintenance and Minor 
> > Extensions WG (tcpm) to consider the following document:
> > 
> > - 'Improving TCP's Robustness to Blind In-Window Attacks '
> >    <draft-ietf-tcpm-tcpsecure-11.txt> as a Proposed Standard
> > 
> > The IESG plans to make a decision in the next few weeks, 
> and solicits 
> > final comments on this action.  Please send substantive comments to 
> > the [e-mail] mailing lists by 2009-04-16. 
> Exceptionally, comments 
> > may be sent to [e-mail] instead. In either case, please retain 
> > the beginning of the Subject line to allow automated sorting.
> > 
> > The file can be obtained via
> > http://www.ietf.org/internet-drafts/draft-ietf-tcpm-tcpsecure-11.txt
> > 
> > 
> > IESG discussion can be tracked via
> > 
> https://datatracker.ietf.org/public/pidtracker.cgi?command=view_id&dTa
> > g=11735&rfc_flag=0
> > 
> > The following IPR Declarations may be related to this I-D:
> > 
> > https://datatracker.ietf.org/ipr/421/
> > 
> > 
> > _______________________________________________
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> > [e-mail]
> > https://www.ietf.org/mailman/listinfo/ietf-announce
> > 
> 
> --
> Fernando Gont
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> 
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