RE: Port-Knocking vulnerabilities?

[<whip () netspace net au>]

> A server that is behind a default-drop packet filter is not
> _practically_ detectable (say, with an nmap scan).  Can you point to a
> piece of software that can reliably perform the timing differences you
> are referring to in order to infer that a server is really listening
> behind such a packet filter?  Do you have to invoke an additional server
> (say, a webserver in addition to an SSH server) that is on the same
> system that is accessible and then making a statistical argument around
> latencies caused by such a server or something like that?

I believe Craig is referring to a Timing Attack.
http://en.wikipedia.org/wiki/Timing_attack

Not really something that you can script for all purposes, but I'm sure
someone with a decent maths grounding could do so for individual attacks,
like this one.


Cheers,
Scott

--
Michael Rash
http://www.cipherdyne.org/
Key fingerprint = 53EA 13EA 472E 3771 894F  AC69 95D8 5D6B A742 839F



> I will get back when I have had a chance to trial it fully.
>
> Regards,
> Dr Craig Wright (GSE-Compliance)
>
> ________________________________________
> From: Michael Rash [mbr () cipherdyne org]
> Sent: Sunday, 6 January 2008 3:12 PM
> To: Craig Wright
> Cc: Goldstein101; Robert Inder; Ansgar -59cobalt- Wiechers;
security-basics () securityfocus com; dave () davekleiman com
> Subject: Re: Port-Knocking vulnerabilities?
>
> On Jan 01, 2008, Craig Wright wrote:
>
> > First, you have mentioned SPA, and true this offers more then port
knocking, you have also mixed port knocking and SPA up in a couple of your
comments.
> > Now you make the comment that SPA can "encrypt" and store in the IP ID.
IP ID is a 16 bit flag. That is there are a max of 65535 values. Even with 4
IP packets it is functionally equivilant to a 3 character password. Given a
standard ADSL line and 68 byte packets I can send all combinations in just
under 7.5 seconds (and this is not doing any analysis on the IPID).
> > That is SPA and not port knocking. That is the MORE secure of the two
options.
> Agreed.
>
> > Yes this way will make a log entry, but are you sitting at the server
24x7 and monitoring ALL scans. Will you stop me in less then 8 seconds?
> > When did people consider a 3 character password safe?
>
> That is why any implementation of SPA that just uses network or
> transport layer headers to communicate information instead of
> application layer data is inherently deficient and not worthy of the
> SPA designation IMHO (even though technically, yes, it is just a single
> packet).
>
> In addition to the small key space that just using the 16 bit IP ID field
> limits any such implementation to, there are additional limitations
> including*:
>
> - Such "SPA" packets are replayable against the target (unless some horrid
>   S/KEY style iteration of a hash function is used or someone manually
>   changes around the key for each SPA packet).  If the application layer
>   were used (such as in fwknop: http://www.cipherdyne.org/fwknop) the
>   replay problem is trivially solved by prepending every SPA packet with
>   16 bytes of random data before it is encrypted.  This is possible
>   because of the relatively large amount of data that can be transfered
>   within the application layer payload of a single UDP packet.
>
> - It is difficult to protect against MITM attacks because the source IP
>   itself in the actual network layer header is allowed through the
>   firewall policy on the server side.  Fwknop allows the source IP to be
>   placed within the encrypted SPA payload, and is therefore not subject to
>   alteration by an attacker that possesses an inline device that can stop
>   an SPA packet and retransmit it with a different source IP.
>
> - It is impossible to communicate client-side information that the
>   server might find useful because the usage of packet headers is too
>   restrictive.  A true SPA implementation can use 2048-bit GnuPG keys
>   and do things like communicate crypt() passwords so the server can
>   interface with additional authentication mechanisms.  Fwknop supports
>   both Rijndael and GnuPG keys, crypt() passwords, and even the
>   transmission of full shell commands.
>
> Here is a list of features supported by fwknop - all of these are
> possible because of the usage of payload data instead of just packet
> headers for SPA communications:
>
> http://www.cipherdyne.org/fwknop/docs/features.html
>
> *Disclaimer: I developed fwknop so obviously I'm biased.  However, I
> welcome any critique that can point out a non-obvious limitation in the
> fwknop architecture or implementation.
>
> --
> Michael Rash
> http://www.cipherdyne.org/
> Key fingerprint = 53EA 13EA 472E 3771 894F  AC69 95D8 5D6B A742 839F
>
>
>
> > Rgards,
> > Dr Craig Wright (GSE-Compliance)
> >
> >
> >
> > Craig Wright
> > Manager of Information Systems
> >
> > Direct : +61 2 9286 5497
> > Craig.Wright () bdo com au
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> >
> > From: listbounce () securityfocus com [listbounce () securityfocus com] On
Behalf Of Goldstein101 [goldstein101 () gmail com]
> > Sent: Tuesday, 1 January 2008 6:40 AM
> > To: Robert Inder
> > Cc: Ansgar -59cobalt- Wiechers; security-basics () securityfocus com
> > Subject: Re: Port-Knocking vulnerabilities?
> >
> > I guess most of you haven't bothered to check what port knocking
> > really is capable of 'cause I'm reading a lot of things that are not
> > true.
> >
> > First of all, Port Knocking is just another layer of security. Think
> > of it as the door of a room that contains a safe. You first have to
> > break the port knocking daemon and then the safe. Not that easy,
> > believe me.
> >
> > Second, Who said port knocking is like transmitting a password in
> > cleartext? Most modern PK systems are encryption based. An attacker
> > can sniff port numbers but packets usually contain other information
> > that is used for authentication.
> >
> > For example I use Aldaba Knocking Suite (aldabaknocking.com) which
> > provides Port Knocking and Single Packet Authorization.
> >
> > In Port knocking mode, basically the client sends this: [IP
> > Address][Port Number][Open/Close Flag][Checksum].
> >
> > That information is encrypted and sent encoded in the IP-Id field of 4
> > TCP-SYN packets. This way you have 2 forms of authentication: The
> > first is simple: you need to know the exact port numbers to use when
> > sending those TCP-Syn Packets. Second: you need to know a secret (the
> > encryption key) used to encrypt the information. If you don't have it,
> > you can send random data but when decrypted, it won't verify the
> > checksum.
> >
> > However, Port Knocking has some disadvantages and vulnerabilities. A
> > better and more elegant approach is SPA. Check it out. There are some
> > papers out there.
> >
> >
> > ..
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> > On Dec 31, 2007 7:27 PM, Robert Inder <robertinder () googlemail com>
wrote:
> > > On 29/12/2007, Ansgar -59cobalt- Wiechers <bugtraq () planetcobalt net>
wrote:
> > > > On 2007-12-28 Jay wrote:
> > > > > Portknocking is a security mechanism as it is a type of
> > > > > authentication. "Something you know" in this case the sequence of
> > > > > ports to knock before a unstarted service or daemon begins
listening
> > > > > for connections.
> > > >
> > > > Since everything is transmitted in the clear port-knocking is as
much of
> > > > a security mechanism as cleartext passwords. Technically: maybe
> > > > (depending on your definition). Realistically: no.
> > >
> > > I think your dismissal of port knocking (and, indeed, plain text
> > > passwords) is unrealistic.
> > >
> > > If you can intercept my interaction with some remote server, you can
> > > steal the relevant secrets (the password or the sequence of ports).
> > >
> > > But isn't that quite a substantial "if"?
> > >
> > > How are you going to do it?  Aren't you going to have to compromise
> > > some other machine, either where I am, or where the server is (or, I
> > > guess, where the relevant DNS records are), and then plant software to
> > > deliberately wait and watch until a relevant interaction takes place?
> > >
> > > I'm not saying that's impossible.  But it would take considerable
> > > knowledge, planning and effort.
> > >
> > > Why doesn't that make it a substantial defence against most kinds of
> > > casual attack?
> > >
> > > Robert.
> > >
> > > --
> > > Robert Inder        Interactive Information Ltd,            Registered
> > > in Scotland
> > > 07808 492 213     3, Lauriston Gardens,                  Company no.
SC 150689
> > > 0131 229 1052     Edinburgh EH3 9HH
> > >                           SCOTLAND UK             Interactions speak
> > > louder than words
> >
> >
> >
> > --
> > Goldstein.
> > Room 101, Ministry of Truth.
> > W2, London. Oceania.

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