Re: [secdir] secdir review of draft-ietf-ospf-encapsulation-cap-06

<bruno.decraene@orange.com> Tue, 19 September 2017 07:18 UTC

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From: <bruno.decraene@orange.com>
To: David Mandelberg <david@mandelberg.org>
CC: "iesg@ietf.org" <iesg@ietf.org>, "secdir@ietf.org" <secdir@ietf.org>, "draft-ietf-ospf-encapsulation-cap.all@ietf.org" <draft-ietf-ospf-encapsulation-cap.all@ietf.org>
Thread-Topic: secdir review of draft-ietf-ospf-encapsulation-cap-06
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Date: Tue, 19 Sep 2017 07:18:42 +0000
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Subject: Re: [secdir] secdir review of draft-ietf-ospf-encapsulation-cap-06
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> From: David Mandelberg [mailto:david@mandelberg.org]
 > Sent: Monday, September 18, 2017 9:30 PM
> 
 > On 09/18/2017 05:08 AM, bruno.decraene@orange.com wrote:
 > >   > (c) is the one that I think is worth looking into. E.g., does this new
 > >   > extension make it easier for an attacker to route a packet across AS
 > >   > boundaries, by setting a tunnel endpoint outside of the OSPF-routed network?
 > >
 > > No. The following text already prohibits even more than this:
 > >
 > > "  A tunnel MUST NOT be
 > >        used if there is no route toward the IP address specified in the
 > >        Endpoint Sub-TLV (See <xref target="EndpointTLV"/>) or if the route is
 > >        not advertised by the router advertising this Tunnel Sub-TLV."
 > >
 > > - By definition, this Tunnel Sub-TLV is advertised in OSPF i.e. from within the AS.
 > > - The text also prohibits setting a tunnel endpoint to another router within the AS.
 > >
 > >
 > > That being said, within the AS, the point "c" still applies.
 > > However, thinking twice, the probability is even more limited. Indeed, one can only advertise a
 > tunnel to itself. Assuming that the third party can't control the whole routing topology (i.e. routing
 > advertisement from most core routers), it cannot control the path followed by the tunnel. Hence it
 > would need to have monitoring capabilities on specific links that it cannot choose. (the link on
 > the path to itself).
 > > Plus this risk is not new, as the third party could already advertise the destination IP address of
 > the packets (or of the BGP Next-hop of the BGP route matching the packet destination), without
 > using any tunnel.
 > > In conclusion, although I could be wrong, I'm not seeing such new risk. (again, assuming that
 > a third party can modify the OSPF routing is a big assumption).
 > >
 > > But the discussion was useful, thanks for the comments.
 > 
 > That explanation is great, thank you. I hadn't realized the implications
 > of the paragraph you quoted, when I initially read it. I'm convinced
 > that there isn't a security issue here, but it would be nice to see your
 > explanation in the document itself, if it's not already obvious to
 > anybody who knows OSPF better than I do.

I've just added the following text in the security section of my local version:
"We note that the last paragraph of <xref target="Operation"/> forbid the establishment of a tunnel toward arbitrary destinations. It prohibits a destination outside of the Autonomous System and also to other routers within the AS. This avoid that a third-party gaining access to an OSPF router be able to send the traffic to other destinations, for e.g. inspection purposes. "

Feel free to comment/propose other text.

Since I've just published -08 a few hours ago, I'll probably delay the upload of this new update.

--Bruno


 > --
 > Freelance cyber security consultant, software developer, and more
 > https://david.mandelberg.org/

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