DNS, Man-in-the-middle??

[Stephen Pedrosa Eilert <spedrosa () mailandnews com>]

---------- Forwarded message ----------
Date: Wed, 6 Aug 2003 03:15:09 -0300 (BRT)
From: Stephen Pedrosa Eilert <spedrosa () mailandnews com>
To: "BUGTRAQ@SECURITYFOCUS. COM" <BUGTRAQ () SECURITYFOCUS COM>
Subject: DNS, Man-in-the-middle??

Posted by mistake on the bugtraq list. Posting here now
---------------------------------------


I has troubleshooting a network problem in some of my computers(will be
called Elderbrain in the remainder of this message) Apparently, it wasn't
receiving any information from my home server(DHCP, DNS cache, NAT,
Firewall, called Speaker).  So, I configured the interface manually, using
my ISP's DNS server and tried to SSH to Speaker. To my surprise, the
following message appeared:

@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@       WARNING: POSSIBLE DNS SPOOFING DETECTED!          @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
The RSA host key for speaker has changed,
and the key for the according IP address 204.91.156.55
is unknown. This could either mean that
DNS SPOOFING is happening or the IP address for the host
and its host key have changed at the same time.
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@    WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!     @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!
Someone could be eavesdropping on you right now (man-in-the-middle
attack)!
It is also possible that the RSA host key has just been changed.
The fingerprint for the RSA key sent by the remote host is
b7:40:14:87:ab:13:fe:9c:90:1f:d3:11:43:dd:59:50.
Please contact your system administrator.
Add correct host key in /root/.ssh/known_hosts to get rid of this message.
Offending key in /root/.ssh/known_hosts:1
RSA host key for speaker has changed and you have requested strict
checking.
Host key verification failed.


Of course, my ISP's DNS server knows nothing about a system called
'speaker', but it replied anyway. Using 'host' on that IP address returns:
55.156.91.204.in-addr.arpa domain name pointer
capawl01.adytumsolutions.com

Incidentally, whenever I mistype a URL, the homepage for that company
appears.

Running NMAP on the IP gives me:

Starting nmap V. 2.54BETA31 ( www.insecure.org/nmap/ )
Interesting ports on capawl01.adytumsolutions.com (204.91.156.55):
(The 1544 ports scanned but not shown below are in state: filtered)
Port       State       Service
22/tcp     open        ssh
25/tcp     open        smtp
80/tcp     open        http
110/tcp    open        pop-3
143/tcp    closed      imap2
443/tcp    open        https
993/tcp    closed      imaps
5801/tcp   closed      vnc-1
6001/tcp   closed      X11:1
8080/tcp   open        http-proxy

Remote operating system guess: Linux Kernel 2.4.0 - 2.4.17 (X86)
Uptime 160.370 days (since Wed Feb 26 18:18:39 2003)

Some suspicious services, if you ask me.

So, how should I proceed from now? Is it possible that the
misconfiguration is with my computer and not theirs? I find it to be
unlikely. It is behind my ISP NAT for my building(so it can only receive
incoming connections from computers inside the building, even then I have
blocked SYN packets at the firewall). Elderbrain is behind Speaker's NAT.
Both are Linux systems.

But how can I be sure? I want to be 100% sure if I am to contact them.



[]'s

Stephen Pedrosa Eilert


'Commit yourself to quality from day one ... it's better to do nothing at
all than to do something badly.'  -Mark H. McCormack



---------------------------------------------------------------------------
----------------------------------------------------------------------------