Re: [OSPF] Fw: New Version Notification for draft-manjuldtv-ospf-sequence-number-00.txt

Hi DTV,

I dont agree to your assessment of how the attack evades the "natural
fight-back mechanism" in OSPF.

Its got *nothing* to do with the sequence numbers being predictable, etc. I
have explained in depth how the Gaby attack works here:

https://routingfreak.wordpress.com/2013/09/09/how-bad-is-the-ospf-vulnerability-exposed-by-black-hat/

Clipped from the blog:

"This attack exploits a potential omission (or a bug if you will) in the
standard where it does not mandate that the receiving router verifies that
the Link State ID and the Advertising Router fields in the Router LSA are
the exact same value.

This attack sends malacious Router LSAs with two different values in the LS
header. The Link State ID carries the Router ID of the router that is being
attacked (the victim) and the Advertising Router is set to some different
(any) value.

When the victim receives the malacious Router LSA, it does not refresh this
LSA as it doesnt recognize this as its own self generated LSA. This is
because the OSPF spec clearly says in Sec 13.4 that “A self-originated LSA
is detected when either 1) The LSA’s Advertising Router is equal to the
router’s own Router ID or 2) the LSA is a network LSA .. “.

This means that OSPF’s natural fight back mechanism is NOT triggered by the
victim router as long as the field ‘Advertising Router’ of a LSA is NOT
equal to the victim’s Router ID. This is true even if the ‘Link State ID’
of that LSA is equal to the victim’s Router ID. Going further it means no
LSA refresh is triggered even if the malacious LSA claims to describe the
links of the victim router!"

I describe further in the blog that not all router implementations are
susceptible to the attack. Its dependent on how the LSA is picked up from
the LSDB.

Cheers, Manav

On Thu, May 12, 2016 at 7:59 AM, Ramakrishna DTV <
ramakrishnadtv@nivettisystems.com> wrote:

> Hi Acee,
>
> We currently provided the following description of this attack in the
> draft:
>
>  "The paper refers to the attack as "Disguised LSA" and is of
>    persistent nature.  This attack is launched from a compromised router
>    inside a routing domain.  In this attack, the compromised router
>    alters the LSA of an uncompromised router (victim).  Normally, such
>    an attempt does not have persistence because the victim generates a
>    new LSA when it sees such self-originated LSAs (referred to as
>    "fight-back" mechanism in the paper).  But the paper makes disguised
>    LSA persistent because all the fields { LS sequence number, checksum}
>    are predictable.  It alters the existing LSA of victim to suit its
>    needs but sets the sequence number to +1 of the existing LSA and
>    alters the LSA so that checksum matches with checksum that would be
>    generated by the victim when it generates the new LSA.  When this
>    disguised LSA reaches the victim, it does not fight back because it
>    compares only the fields { LS sequence number, checksum, age} to
>    check for duplicates and not the actual content of LSA.
>
>    This attack enables an insider attacker to fully control the entire
>    content of an LSA.  We think this attack is powerful."
>
> These details are currently present in Section 4, which is titled
> "Implementation advice".
> We can probably move it to a different section (e.g., "Introduction") to
> make it clear.
>
> If you think even more additional details about the attack are useful to
> the working group,
> please let us know. We will add.
>
> Thank you.
>
> Regards,
> Ramakrishna DTV.
>
>
> ________________________________________
> From: Acee Lindem (acee) <acee@cisco.com>
> Sent: Wednesday, May 11, 2016 8:49 PM
> To: Manjul Khandelwal; ospf@ietf.org
> Cc: Ramakrishna DTV
> Subject: Re: [OSPF] Fw: New Version Notification for
> draft-manjuldtv-ospf-sequence-number-00.txt
>
> Hi Manjul,
>
> Would it be possible to succinctly describe these “certain security
> attacks” in the draft rather than expecting everyone to read the
> referenced paper?
>
> Thanks,
> Acee
>
> On 5/11/16, 10:19 AM, "OSPF on behalf of Manjul Khandelwal"
> <ospf-bounces@ietf.org on behalf of manjul@nivettisystems.com> wrote:
>
> >Hi,
> >
> >We have recently submitted a draft which deals with OSPF LS sequence
> >number
> >generation mechanism.
> >
> >Abstract of the draft:
> >   The mechanism for LS sequence number generation as specified in RFC
> >   2328 and RFC 5340 is completely predictable.  This makes it prone to
> >   certain security attacks which exploit the predictable nature of LS
> >   sequence numbers.  This draft updates the RFC 2328 to make LS
> >   sequence number generation an implementation choice rather than a
> >   fixed increment by 1 for successive LSAs.
> >
> >https://datatracker.ietf.org/doc/draft-manjuldtv-ospf-sequence-number/
> >
> >We solicit feedback/comments on the draft and request for adoption by the
> >OSPF working group.
> >
> >Regards,
> >Manjul Khandelwal
> >DTV Ramakrishna Rao
> >________________________________________
> >From: internet-drafts@ietf.org <internet-drafts@ietf.org>
> >Sent: Monday, May 9, 2016 7:22 PM
> >To: Manjul Khandelwal; Ramakrishna DTV
> >Subject: New Version Notification for
> >draft-manjuldtv-ospf-sequence-number-00.txt
> >
> >A new version of I-D, draft-manjuldtv-ospf-sequence-number-00.txt
> >has been successfully submitted by Manjul Khandelwal and posted to the
> >IETF repository.
> >
> >Name:           draft-manjuldtv-ospf-sequence-number
> >Revision:       00
> >Title:          OSPF LSA sequence number generation
> >Document date:  2016-05-09
> >Group:          Individual Submission
> >Pages:          10
> >URL:
> >
> https://www.ietf.org/internet-drafts/draft-manjuldtv-ospf-sequence-number-
> >00.txt
> >Status:
> >https://datatracker.ietf.org/doc/draft-manjuldtv-ospf-sequence-number/
> >Htmlized:
> >https://tools.ietf.org/html/draft-manjuldtv-ospf-sequence-number-00
> >
> >
> >Abstract:
> >   The mechanism for LS sequence number generation as specified in RFC
> >   2328 and RFC 5340 is completely predictable.  This makes it prone to
> >   certain security attacks which exploit the predictable nature of LS
> >   sequence numbers.  This draft updates the RFC 2328 to make LS
> >   sequence number generation an implementation choice rather than a
> >   fixed increment by 1 for successive LSAs.
> >
> >
> >
> >
> >Please note that it may take a couple of minutes from the time of
> >submission
> >until the htmlized version and diff are available at tools.ietf.org.
> >
> >The IETF Secretariat
> >
> >_______________________________________________
> >OSPF mailing list
> >OSPF@ietf.org
> >https://www.ietf.org/mailman/listinfo/ospf
>
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