Re: [secdir] Secdir review of draft-ietf-6man-flow-ecmp-03
Brian Weis <bew@cisco.com> Tue, 05 July 2011 19:44 UTC
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From: Brian Weis <bew@cisco.com>
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Date: Tue, 05 Jul 2011 12:44:34 -0700
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References: <571B7ACD-26B9-4A46-9791-0EA76134A585@cisco.com> <4E0EE3D8.9040500@piuha.net> <4E0F0B53.2080809@gmail.com> <7CDA80AB-6144-4449-86AB-5F659AD97243@cisco.com> <4E13653F.5090707@gmail.com>
To: Brian E Carpenter <brian.e.carpenter@gmail.com>
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Cc: draft-ietf-6man-flow-ecmp.all@tools.ietf.org, Jari Arkko <jari.arkko@piuha.net>, iesg@ietf.org, secdir@ietf.org
Subject: Re: [secdir] Secdir review of draft-ietf-6man-flow-ecmp-03
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On Jul 5, 2011, at 12:25 PM, Brian E Carpenter wrote: > On 2011-07-06 06:22, Brian Weis wrote: >> Hi Brian C, >> >> On Jul 2, 2011, at 5:13 AM, Brian E Carpenter wrote: >> >>>> If the attacker can provide all of the inputs, and it knows the tunnel >>>> endpoint flow label calculation, then there doesn't seem to be any unpredictability. >>> That's correct, and means that if you are concerned about this risk, >>> there needs to be an obfuscation step in the hash algorithm. >> >> Right, but obfuscation is kind of a loaded word. Adding an input to the hash algorithm that the attacker is unlikely to guess will mitigate the risk, and this is probably what you meant. > > Yes, I agree and that really belongs in the 3697bis draft, whose Last Call is > running a bit behind this one. I will come up with some wording before the > I-D cutoff. That's fine with me. Thanks, Brian Weis > > Brian > >> Brian Weis >> >>>> (The I-D says to see [I-D.ietf-6man-flow-3697bis] for further discussion >>>> of this threat. I can't seem to find it, but if it's there simply pointing >>>> to that discussion would be fine too.) >>> I think it would be better to include any additional wording in 3697bis >>> - can we look at this when we get the security review of that draft? >>> I think Brian W is correct that it needs to be added. >>> >>> Regards >>> Brian Carpenter >>> >>> On 2011-07-02 21:24, Jari Arkko wrote: >>>> Thanks for your review, Brian. I do agree that the issue that you >>>> mention should be explained better. Authors, please suggest some text. >>>> >>>> Jari >>>> >>>> Brian Weis kirjoitti: >>>>> I have reviewed this document as part of the security directorate's >>>>> ongoing effort to review all IETF documents being processed by the >>>>> IESG. These comments were written primarily for the benefit of the >>>>> security area directors. Document editors and WG chairs should treat >>>>> these comments just like any other last call comments. >>>>> >>>>> Intermediate systems in a routing system perform load balancing of >>>>> packets between a pair of nodes based on values in the packet. This >>>>> I-D defines a safe method by which the IPv6 flow label can be one of >>>>> those values. A necessary condition is that flow labels that have a >>>>> uniform distribution, and the method is restricting to use by IPv6 >>>>> tunnel endpoints that are more trusted to apply this method to packets >>>>> they encapsulate. >>>>> >>>>> The Security Considerations section describes a single availability >>>>> attack, which is an attacker able to "selectively overload a >>>>> particular path". I assume that this can happen if the hash >>>>> calculation of the intermediate systems will send too many packets >>>>> down one path and overload it rather than properly load balancing >>>>> across the paths. The values used by the intermediate system come from >>>>> packet headers, and the calculation is deterministic. If the flow >>>>> label computed by the tunnel endpoint is included in the calculation, >>>>> and it is also deterministic, then it seems that an attacker knowing >>>>> the method used by the tunnel endpoint to create flow labels can >>>>> engage in this attack. That is, the attacker crafting packets that >>>>> will result in the tunnel end point computing one or more flow labels >>>>> that cause the intermediate system to include in its hash calculation, >>>>> which results in it routing over the same path. This may be feasible >>>>> for an informed attacker controlling a suitable size botnet. So making >>>>> the tunnel endpoint flow label calculation unpredictable would be >>>>> important to stop this attack. >>>>> The I-D recommends computing the flow label according to >>>>> [I-D.ietf-6man-flow-3697bis], and also states in Section 3 that the >>>>> result "will be hard for a malicious third party to predict". If so, >>>>> then this attack seems mitigated when the recommendation is taken. But >>>>> it would be helpful if the Security Considerations could also mention >>>>> the need for unpredictability, and perhaps also mention how the >>>>> unpredictability is added. As far as I can tell, the recommendation in >>>>> [I-D.ietf-6man-flow-3697bis] is to build the flow label from values in >>>>> the packet being encapsulated, which the attacker itself may have >>>>> generated. If the attacker can provide all of the inputs, and it knows >>>>> the tunnel endpoint flow label calculation, then there doesn't seem to >>>>> be any unpredictability. (The I-D says to see >>>>> [I-D.ietf-6man-flow-3697bis] for further discussion of this threat. I >>>>> can't seem to find it, but if it's there simply pointing to that >>>>> discussion would be fine too.) >>>>> >>>>> Other than clarifying how that attack is mitigated I do not see the >>>>> need for any changes. >>>>> Brian >>>>> >>>> >>>> >> >> -- Brian Weis Security Standards and Technology, SRTG, Cisco Systems Telephone: +1 408 526 4796 Email: bew@cisco.com
- [secdir] Secdir review of draft-ietf-6man-flow-ec… Brian Weis
- Re: [secdir] Secdir review of draft-ietf-6man-flo… Jari Arkko
- Re: [secdir] Secdir review of draft-ietf-6man-flo… Brian E Carpenter
- Re: [secdir] Secdir review of draft-ietf-6man-flo… Brian Weis
- Re: [secdir] Secdir review of draft-ietf-6man-flo… Brian E Carpenter
- Re: [secdir] Secdir review of draft-ietf-6man-flo… Brian Weis