RE: Sensationalism? [was Re: FW: Man in the middle attack against RFC3456.]

[Van Aken Dirk <VanAkenD@thmulti.com>]

I agree with Scott, IPSec is not going to solve this kind of security
issues.
i.e. IPSec was not conceived to cope with the situation where the frontdoor
is open and where there is no backdoor.
People having access to a central offices are assumed to be trusted !

I would agree with you Darren, if this same scenario would work form the VPN
client side because there is far less control on who is sitting behind the
VPN client.

If you can convice me that ModeCfg has no inherent limitations or that the
DHCP based method has serious flaws, please tell me. If so, I'm willing to
change my religion.


BTW If IPSec must also cope with malicous insiders, then I know a very
simple but effective attack on the security solution provided by a certain
company ...


> -----Original Message-----
> From: Scott G. Kelly [mailto:scott@bstormnetworks.com]
> Sent: woensdag 5 februari 2003 20:52
> To: ddukes@cisco.com
> Cc: ipsec@lists.tislabs.com
> Subject: Sensationalism? [was Re: FW: Man in the middle attack against
> RFC3456.]
> 
> 
> Come on, Darren - you must be joking. What you describe is 
> not an attack
> against RFC3456 - it's an attack against DHCP/BOOTP, and this 
> is nothing
> new. If you run DHCP on your network and you have malicious insiders,
> they can do all sorts of things. The same applies for most other
> commonly run lan protocols. And since you've already conceded that a
> scalable modecfg implementation will be running dhcp on the backend,
> what is the point of this post? 
> 
> Let's stick with arguments with technical merit.
> 
> Scott
> 
> Darren Dukes wrote:
> > 
> > Amendment:
> > Eve sends the DHCPACK to the DHCP-relay (not the IRAC) with 
> a manufactured
> > DHCP Relay Agent Information Option or one copied from a 
> previous DHCP
> > message.
> > 
> > > -----Original Message-----
> > > From: Darren Dukes [mailto:ddukes@cisco.com]
> > > Sent: Wednesday, February 05, 2003 12:10 PM
> > > To: ipsec@lists.tislabs.com
> > > Subject: Man in the middle attack against RFC3456.
> > >
> > >
> > > There is a man in the middle attack on the DHCP-relay in RFC3456.
> > > This attack is based on the thread defined in RFC3118
> > > (DHCP-AUTH).  In this case Eve is inside the LAN and able to
> > > source DHCPACK packets, if Eve sends a DHCPACK to a an IRAC via a
> > > SGW implementing RFC3456 the DHCP-relay on the SGW will plumb a
> > > new route for whatever address Eve puts in yiaddr.
> > >
> > >                |-Eve
> > > IRAC ---- SGW -|
> > >                |-DHCP Server
> > >
> > > excerpt from RFC3456:
> > >    To learn the internal IP address of the client in 
> order to route
> > >    packets to it, the security gateway will typically 
> snoop the yiaddr
> > >    field within the DHCPACK and plumb a corresponding 
> route as part of
> > >    DHCP Relay processing.
> > >
> > > This attack is not resolved by the implementation of RFC3118
> > > unless the following changes are made to the DHCP-relay.
> > > 1 - It stored a copy of all secret keys contained on the
> > > DHCP-server and used them to authenticate DHCPACKs or it stored a
> > > copy of the master key and used that to generate the client keys
> > > as described in RFC3118 Appendix A.
> > > 2 - DHCP-relay implements the DHCP-server replay protection.
> > >
> > >
> > > Darren
> > >
>