OSPF Vulnerability - Owning the Routing Table

Saku Ytti saku at ytti.fi
Sun Aug 4 08:17:03 UTC 2013


On (2013-08-03 18:38 -0500), Jimmy Hess wrote:

> That's not news to me, but fully expected.
> Do the vendors /really/  have a code fix to  what would seem to be an
> inherent problem;  if you failed to properly secure your OSPF
> implementation (via MD5 authentication)?

It is news to me. It's design flaw in the protocol itself which has gone
unnoticed for two decades and I would have naively fully expected that this
flaw does not exist in standard.

As I've understood issue lies in the fact that 'link state id' and
'advertising router' should always be the same (so it's redundant
information in the LSA, single field should suffice?). But standard does
not enforce this at all.
Victim will omit doing corrective reflood for received bogus LSA if
'advertising router' is something else than 'router-id', even while 'link
state id' == 'router-id'

I suppose vendors implement fix where either
  a) corrective reflood occur if 'link state id' == 'router-id'
  or
  b) LSA is rejected unless 'link state id' == 'advertising router'

How serious or new this is, may be debatable, as only thing it seems
remove, is the need for attacker to inject 0.2pps worth of packets which
will suppress the corrective reflooding.

-- 
  ++ytti



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