RE: Port-Knocking vulnerabilities?

["Bill Lavalette" <blavalet () homenet-security com>]

I think Brent was right in saying get a real Firewall/VPN installed. I
believe the original thread on this was that there was a weird ssh mech that
the user found and was wondering why. We have swayed way past the advice
point on this thread IMHO. It appears that the company in question is using
a practice that was acceptable in the mid 90's If this is a risk that the
business owners are willing to accept then there is nothing this list is
going to gain or achieve by getting emotional about it. The best advice we
can give this person is to advise the business owners that they are in dire
need of a security overhaul and move forward. Heck I remember when port
sentry was the hot ticket. I must say thought I think Craig  in another
thread mentioned gains and losses, From a business perspective He is right
and some of you may interpret his words differently, Acceptable Risk is
another way we understand this.

Have a Happy and Prosperous 2008 all

Bill

====== HomeNet Security ===========
Bill Lavalette 
Network Security Officer
CCSA-CCSE 
Crisis Mitigator
ID Theft Prevention Mentor
WWW http://www.homenet-security.com
====================================
     Defending The Home LAN



-----Original Message-----
From: listbounce () securityfocus com [mailto:listbounce () securityfocus com] On
Behalf Of Craig Wright
Sent: Monday, December 31, 2007 4:46 PM
To: Ansgar -59cobalt- Wiechers; security-basics () securityfocus com
Cc: lbhlists () gmail com; dave () davekleiman com
Subject: RE: Port-Knocking vulnerabilities?

Lets look at the issues.

You rely on obscurity in a manner that changes flags in IP and makes the
packets stand out. Most IDS's will alert to this, many routers will. A
TCPdump filter for unusual flags and IP ID's is common in many ISP's. So we
have a security mechanism that is advertising itself but relies on secrecy.
Paradox and inconsistency No. 1.

The IP ID field is 16 bits. With a 4 packet knock we have a functional
equivalent of a 3 character all symbol or 4 character alpha numeric
password. I do not believe that this was ever considered secure.

IP ID fingerprinting will make the flag stand out. Without the SPA
encryption mechanisms it is a simple capture (or sniffing). Using SPA (not
Port knocking) you can sniff packets and capture for analysis. The
"encryption" can be silently cracked in seconds (it is functionally
equivalent to 13 bit DES) in microseconds given any modern PC.

 Please explain how this is more than a script kiddie toy and a security
boon?

 As Brent stated, why not deploy a REAL crypto solution. It is 1. Easier. 2.
Supported and 3 More secure (i.e. 128 or 256 bit keys take a LONG time to
break).

Regards,
Dr Craig Wright (GSE-Compliance)
PS Happy New Year





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 Ansgar -59cobalt- Wiechers [bugtraq () planetcobalt net]
Sent: Tuesday, 1 January 2008 7:50 AM
To: security-basics () securityfocus com
Subject: Re: Port-Knocking vulnerabilities?

On 2007-12-31 Robert Inder 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"?

The substantial "if" is the question if intercepting the transmission will
allow an attacker to learn the secret without having to compromise either
the sender or the receiver of the communication. If an attacker can do that,
then the authentication mechanism is insecure and thus mere obscurity.
Period.

> 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?

http://ettercap.sourceforge.net/

There are other attack vectors as well.

> 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?

Because "substantial" is the opposite of "casual". A measure that won't also
stop a determined attacker is just obscurity, not security.

Regards
Ansgar Wiechers
--
"All vulnerabilities deserve a public fear period prior to patches becoming
available."
--Jason Coombs on Bugtraq

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