Re: [secdir] Secdir review of draft-ietf-6man-flow-ecmp-03
Brian Weis <bew@cisco.com> Tue, 05 July 2011 18:22 UTC
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From: Brian Weis <bew@cisco.com>
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Date: Tue, 05 Jul 2011 11:22:27 -0700
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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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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. 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