Re: [rtcweb] Consent alternative
"Muthu Arul Mozhi Perumal (mperumal)" <mperumal@cisco.com> Tue, 03 December 2013 04:30 UTC
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From: "Muthu Arul Mozhi Perumal (mperumal)" <mperumal@cisco.com>
To: Martin Thomson <martin.thomson@gmail.com>, Magnus Westerlund <magnus.westerlund@ericsson.com>
Thread-Topic: [rtcweb] Consent alternative
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Date: Tue, 03 Dec 2013 04:30:13 +0000
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Cc: "Cullen Jennings (fluffy)" <fluffy@cisco.com>, "rtcweb@ietf.org" <rtcweb@ietf.org>
Subject: Re: [rtcweb] Consent alternative
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|2. B (the attacker) triggers an "ICE restart" with A, though really |this generates a new ICE negotiation with a victim, C. C consents to |talk to B, but not necessarily with A. This arrangement is easy to |achieve on the drive-by web. | |3. A completes ICE with C and expects to continue the DTLS connection |over the newly discovered 5-tuple. Assuming this is a regular ICE restart, the STUN binding requests sent as part of the ICE connectivity checks from A to C would have randomly generated transaction IDs. Unless B is on the A-C path or can guess those transaction IDs, it wouldn't be able to generate legitimate binding responses to cause ICE to conclude b/w A and C. Muthu |-----Original Message----- |From: rtcweb [mailto:rtcweb-bounces@ietf.org] On Behalf Of Martin Thomson |Sent: Tuesday, December 03, 2013 4:14 AM |To: Magnus Westerlund |Cc: Cullen Jennings (fluffy); rtcweb@ietf.org |Subject: Re: [rtcweb] Consent alternative | |On 29 November 2013 05:40, Magnus Westerlund |<magnus.westerlund@ericsson.com> wrote: |> I have looked briefly on this and wonder if this isn't vulnerable to |> active attacks from a attacker (Alice) that likes to use a set of WebRTC |> browsers, including (Bob) to generate DDOS traffic towards the target |> (Charlie). | |Hi Magnus, | |I think that you did manage to hit on something critical here. | |The basic security primitive in play with ICE consent is proof of |receipt. That is the key piece at play here as well. We require |proof of receipt simply because that elevates the requirements for an |attacker to the point that they have to basically be on-path. At that |point, they (likely) already have the ability to generate traffic |toward a victim of an equal (or maybe greater) volume to the sender |and gain little by mounting the attack. | |That's why I'm not particularly interested in the part where you talk |about attackers intercepting binding requests. | |The actual attack that you have hit upon (or caused me to think about) |is not quite as you described, but it does rely on the fact that the |proposed change to the consent mechanism no longer actively depends on |proof of receipt. | |It also relies on the possibility that a DTLS connection can be moved |without requiring proof of receipt on the new path. That, to me, is |the fundamental problem to be solved. From my reread of RFC 6347, it |appears as though the only consideration given to DoS was at the |handshake. Once something like ICE is in play (and MICE makes this |worse), the ability to "move" the connection presents an attacker with |an opportunity. (I have to point out that this also confirms my fears |about the mechanism used to signal ICE restarts, but I'll get back to |that.) | |Here is the attack as I understand it: | |1. A talks to B, establishing a DTLS connection using ICE. There is |no need for lots of data to flow at this point, this is the "warm-up" |phase of the attack. | |2. B (the attacker) triggers an "ICE restart" with A, though really |this generates a new ICE negotiation with a victim, C. C consents to |talk to B, but not necessarily with A. This arrangement is easy to |achieve on the drive-by web. | |3. A completes ICE with C and expects to continue the DTLS connection |over the newly discovered 5-tuple. C is confused, but really has no |recourse at this point. Even if the DTLS connection fails, C is now |the victim on the other end of an unending stream of bits. B spoofs |the source address of the necessary packets to continue consent, A |continues to send to C, and nothing that C does can stop the flood |because they don't have access to the master secret and cannot |therefore produce an authenticated packet that terminates the |connection. B can continue the attack as long as A is willing, at the |bargain-basement price of a (spoofed) DTLS heartbeat response every |10-20 seconds. | |The key here is the lack of a proof of receipt from A toward C for the |DTLS connection that is moved. There is nothing inherent to DTLS that |provides proof that C received data from A and is also willing to |continue to communicate... Almost. | |The DTLS heartbeat extension does provide such a thing: |http://tools.ietf.org/html/rfc6520#page-6 | |All we need to do to close this little loophole is to require that a |DTLS heartbeat request be sent after any change in underlying 5-tuple. | That request MUST contain sufficient entropy that guessing would be |difficult for an off-path attacker; noting that this is also covered |by TLS record layer encryption and authentication, limiting the number |of parties that are even allowed to make a guess. I'm a big fan of |128 bits, but less is almost certainly OK. If no response is received |within N seconds, consent is expired. The basic consent timer seems |appropriate here, i.e., N=30. | |DTLS renegotiation would also work, but I consider that to be a little |heavyweight. I'm not sure that it's that widely implemented either. |_______________________________________________ |rtcweb mailing list |rtcweb@ietf.org |https://www.ietf.org/mailman/listinfo/rtcweb
- [rtcweb] Consent alternative Martin Thomson
- Re: [rtcweb] Consent alternative tim panton
- Re: [rtcweb] Consent alternative Bernard Aboba
- Re: [rtcweb] Consent alternative Martin Thomson
- Re: [rtcweb] Consent alternative tim panton
- Re: [rtcweb] Consent alternative Martin Thomson
- Re: [rtcweb] Consent alternative Lorenzo Miniero
- Re: [rtcweb] Consent alternative Martin Thomson
- Re: [rtcweb] Consent alternative Magnus Westerlund
- Re: [rtcweb] Consent alternative Martin Thomson
- Re: [rtcweb] Consent alternative Muthu Arul Mozhi Perumal (mperumal)
- Re: [rtcweb] Consent alternative Martin Thomson
- Re: [rtcweb] Consent alternative Muthu Arul Mozhi Perumal (mperumal)
- Re: [rtcweb] Consent alternative Martin Thomson
- Re: [rtcweb] Consent alternative Dan Wing
- Re: [rtcweb] Consent alternative Muthu Arul Mozhi Perumal (mperumal)
- Re: [rtcweb] Consent alternative Martin Thomson
- Re: [rtcweb] Consent alternative Martin Thomson
- Re: [rtcweb] Consent alternative Dan Wing
- Re: [rtcweb] Consent alternative Martin Thomson
- Re: [rtcweb] Consent alternative Muthu Arul Mozhi Perumal (mperumal)
- Re: [rtcweb] Consent alternative Muthu Arul Mozhi Perumal (mperumal)
- Re: [rtcweb] Consent alternative Martin Thomson
- Re: [rtcweb] Consent alternative Martin Thomson
- Re: [rtcweb] Consent alternative Tirumaleswar Reddy (tireddy)
- Re: [rtcweb] Consent alternative Harald Alvestrand
- Re: [rtcweb] Consent alternative Tirumaleswar Reddy (tireddy)
- Re: [rtcweb] Consent alternative Martin Thomson
- Re: [rtcweb] Consent alternative Tirumaleswar Reddy (tireddy)