Enno, As you probably know, Cisco handles PSIRT issues with care, so, I have no clue on this specific advisory. My own (educated) guess is that the packet causing a LC reload is fully RFC 2460 compliant but unusual, so, probably (a guess again) a combination of extension headers triggering a bug.
In this specific case, I would not blame IPv6 or RFC 2460 but rather my own company (even if the affected versions were quite old as new IOS-XR versions appear to be immune to this bug). And I appreciate the humor in your rhetorical question about which FW could protect a CRS... Air gap probably :-) More generally, regarding the 'parsing of the header' and performance, my understanding (and I am NOT a HW engineer) is that there are multiple ways to parse the header chain: - purely software in low-end devices, should have a marginal performance impact - specific ASIC in middle-end devices (read high end enterprise), probably some limitations and heavy performance impact (but again within one organization, so, easier to fix the root cause) - a lot of specialized network processors in high-end devices (SP gears), which is a similar case as the 'low-end device', performance impact but marginal as parsing the chain of headers is not that hard after all _when_ coded correctly As the extension headers are specific to IPv6, this is an area when we will all learn (and have learned already) a lot of things... I respectfully disagree with your last sentence. Of course, destination AS/host SHOULD only accept useful, known and legit ext headers; but, why would an ISP filter on ext headers if they do not harm their own infra or a customer infra? Do you envision an Internet where only TCP/443 and UDP/43 would be accepted? Last point, the Internet will have to use IPv6 for 10 or 20 years at least. If the IETF/ISP block all new _options_ in _existing_ extension headers, then we will be stuck in 1997 for network innovation. While I do not like taking security risks, I even fear more the lack of innovation. Let's talk on Thursday at Silvia's IPv6 Conference in Zurich ;-) -éric On 11/06/15 11:58, "Enno Rey" <[email protected]> wrote: > >the problem here is the definition of "normal IP packet" as of RFC2460. >To illustrate this I just quote from today's Cisco advisory (Cisco IOS XR >Software Crafted IPv6 Packet Denial of Service Vulnerability) on packets >potentially crashing CRS-3 line cards: > >"The vulnerability is due to incorrect processing of an IPv6 packet >carrying IPv6 extension headers that are valid but unlikely to be seen >during normal operation. An attacker could exploit this vulnerability by >sending such an IPv6 packet to an affected device that is configured to >process IPv6 traffic. An exploit could allow the attacker to cause a >reload of the line card, resulting in a DoS condition." > >two question come to mind here: > >- is a "valid but unlikely" extension header chain "normal"? >- what ("combination of FW & IPS or whatever") would you put in front of >a CRS? > >my (sad) expectation is that we'll see much more of these (types of) >issues in the future. given the current level of freedom that the RFC2460 >leaves (see also discussion/picture in >http://www.insinuator.net/2015/06/is-ipv6-more-secure-than-ipv4-or-less/) >"properly parsing an IPv6 packet, let alone in wire speed" seems a pretty >much unsolvable task to me. > >That said I still fail to see any useful extension header besides AH&ESP >(not even FH) to be transported in the Internet. > >best > >Enno > > > > > > > > If your firewall cannot implement this policy, then >> it is time to change or to use a combination of FW & IPS or whatever. >> >> - network person: as I will live with IPv6 for the rest of my life, >>then I >> want a way to extend it and I need any packet to travel to my source to >>my >> destination. Any IPv6 packet should be able to traverse the >> Internet/private network as long as its layer-3 header is valid >> (filtering/dropping can be done exceptionally for good operational >> reason). Did we remember the IPv4 teardrop attack? It is blocked by >> default by most routers for years ;-) >> >> Bugs will plague us for ever... And make our life more complex than the >> above description of course ;-) >> >> -??ric >> >> On 17/05/15 20:43, "Silvia Hagen" <[email protected]> wrote: >> >> >Hi >> > >> >I keep stumbling about that "recommendational wording" in RFC 2460 >> >everytime I teach it. >> > >> >Couldn't we update RFC2460 and make this list a strict order? >> > >> >I would want my firewall to notify me if the EHs in a packet do not >> >follow the list. >> >And limiting the number of possible EHs per packet might be a good >>idea. >> > >> >Silvia >> > >> >-----Urspr??ngliche Nachricht----- >> >Von: ipv6-wg [mailto:[email protected]] Im Auftrag von Benedikt >> >Stockebrand >> >Gesendet: Sonntag, 17. Mai 2015 18:39 >> >An: [email protected] >> >Betreff: Re: [ipv6-wg] Extension Headers / Impact on Security Devices >> > >> >Hi Enno and list, >> > >> >Enno Rey <[email protected]> writes: >> > >> >> hope everybody had a great #RIPE70 meeting. We did! >> >> Many thanks to the organizers and chairs! >> > >> >and thanks to the actual speakers as well the speakers we had to turn >> >down due to time constraints, too:-) >> > >> >> If the chairs consider this appropriate we will happily give a >> >> presentation on this stuff in Bucharest or at another occasion. >> > >> >Sounds good to me! >> > >> >> - looking at the "liberty" RFC2460 provides as for ext_hdrs (wrt to >> >> their number, order[...] >> > >> >Actually, as far as I'm concerned that's the real core of the problem. >> >Or more specifically, the first two lines of RFC 2460, section 4.1: >> > >> > When more than one extension header is used in the same packet, it >>is >> > recommended that those headers appear in the following order: >> > >> >followed on the next page by >> > >> > Each extension header should occur at most once, except for the >> > Destination Options header which should occur at most twice (once >> > before a Routing header and once before the upper-layer header). >> > >> >Note in particular that these are not even RFC 2119 "SHOULD" or >> >"RECOMMENDED" and such. >> > >> >The impact here is actually at least twofold: >> > >> >- It is impossible to implement this as a simple pipeline architecture >> > in hardware; at least for cases deviating from the "recommendations" >> > above this effectively becomes either excessively complex to >>implement >> > in hardware or an invitation to DoS when implemented in software on >>an >> > otherwise hardware router. >> > >> >- As I understand it, at least some of the issues you have found are >> > effectively based on violating the second paragraph quoted, making it >> > impossible to come up with a lower bound on how long the header chain >> > can actually get and therefore leading to the fragmentation related >> > attacks and similar you have discovered. >> > >> >The original idea was that the extension headers are processed strictly >> >in the order they occur, so one question to ask is if there is any >>valid >> >reason to violate these "recommendations" for other than malicious >> >purposes. >> > >> > >> >Cheers, >> > >> > Benedikt >> > >> >-- >> >Benedikt Stockebrand, Stepladder IT >>Training+Consulting >> >Dipl.-Inform. http://www.stepladder-it.com/ >> > >> > Business Grade IPv6 --- Consulting, Training, Projects >> > >> >BIVBlog---Benedikt's IT Video Blog: >>http://www.stepladder-it.com/bivblog/ >> > >> > >> > >-- >Enno Rey > >ERNW GmbH - Carl-Bosch-Str. 4 - 69115 Heidelberg - www.ernw.de >Tel. +49 6221 480390 - Fax 6221 419008 - Cell +49 173 6745902 > >Handelsregister Mannheim: HRB 337135 >Geschaeftsfuehrer: Enno Rey > >======================================================= >Blog: www.insinuator.net || Conference: www.troopers.de >Twitter: @Enno_Insinuator >======================================================= > >_______________________________________________ >v6ops mailing list >[email protected] >https://www.ietf.org/mailman/listinfo/v6ops
