Re: compromised machines

["Brian Eckman" <eckman () umn edu>]

Are you sure they were compromised "through" IRC bots, or just that they had
them installed? It wouldn't surprise me if they were running bots, but I'd
guess they were XDCC bots to serve up the Warez, and not something like
Agobot, Polybot or Spybot, which compromise computers. They were probably
compromised via weak Windows account passwords. This is pretty common in the
FxP scene. They get a hold of one host in your network, then install a
backdoor like VNC, Radmin or even the built-in Windows Telnet Server
(sometimes configured to run on a high port), then use that computer to
launch attacks at the rest. This prevents your edge IDS from noticing the
mass amounts of password guessing.

AntiVirus won't detect their kits, because there is nothing malicious in
them. Eggdrop (or similar), ServU FTP (most common, but occasionally another
will be used), psexec and Radmin are good admin tools. It's just unfortunate
when someone who shouldn't be an admin installs them on your box.

The Windows 2000 boxes might be probed for a list of user accounts and have
a list of passwords thrown at all of the accounts that are a member of the
Administrators account. This is simple, as Windows 2000 by default allows
the enumeration of users and groups via a null session. This makes them much
easier targets, as they might have a very difficult to guess Administrator
account, but when the username is joeblow and the password is joeblow, and
that user is a member of the administrators group, it becomes trivial for
these folks to compromise it.

Windows XP is a little tougher, as the enumeration of users and groups via a
null session is turned off by default. However, it is extremely likely that
an account called "administrator" exists and is a member of administrators,
so they will typically throw guesses at that account when they can't get a
list of usernames.

If they crack a multi user computer (Windows 2000 Server comes to mind),
they will sometimes run pwdump2 or pwdump3 to get a list of hashes, then try
to obtain the other user accounts' passwords that way. Then, they'll add
those passwords to their dictionary. Also, their scanning tool typically
tries the username as the password, so if you have a username not in their
dictionary, but their password is the same as their username, it'll get
0wned, and they'll add that to their dictionary too.

To catch them accessing their FTP backdoor (hey, prevention is ideal, but
detection is a *must*), add a Snort rule similar to this:

alert tcp $EXTERNAL_NET 1025: -> $HOME_NET !21 (msg: \
"non-standard ftp daemon log in"; content:"USER "; depth:5; offset:0; \
dsize:<25; nocase; classtype:trojan-activity;)

You'll have to tune the above some, as it will have false positives with POP
logons and Sasser backdoor attempts, along with others I'm sure. You can
always change it to "$HOME_NET 6544", but if they change ports on you,
you're blind again.

To prevent this (ideal), implement a password policy. Get approval from
management to use the hacker tools against your own network, looking for
boxes with weak authentication. Preferably use something like LC5 which
won't tell you the password, just that it was broken (CYA). Tell users they
have to turn off File and Print sharing unless it is absolutely necessary to
do their job. Tell admins to remove the ability of people to enumerate users
and groups via a NULL session, on their workstations and servers. Require
that server admins remove LANMAN hashes from their server, so when it gets
hacked, the SAM file on it isn't a goldmine of passwords, but instead at
least makes the attackers work for their keep.

Brian
--
Brian Eckman
Security Analyst
University of Minnesota

----- Original Message ----- 
From: "Varun Pitale" <varun.pitale () gmail com>
To: <incidents () securityfocus com>
Sent: Thursday, August 26, 2004 1:35 PM
Subject: compromised machines


last week, I had around 78 machines compromised through IRC bots and
all of them running a ftp server on port 6544 with the following
banner:

220-Serv-U FTP Server v5.0 for WinSock ready...
220-.
220-.
220-           ¨¨°º©o.,,.o©  HacKed By EvilzCrew  ©o.,,.o©º°¨¨
220-.
220-.
220-
220-                       ---=   SERVER ---
220----->  Le Server est Up depuis 0 Jour: 14 Heure: 52 Min
220----->  Nous somme le Saturday 14 August, 2004 il est 14:27:36 Sur le
Server
220-
220-                      ---=   TRANSFERTS ---
220-----> Vitesse : moyenne :   0.261 kb/sec
220-----> Download total :              20 Kb
220-----> Upload total :                13977 Kb
220-
220-                      ---=   UTILISATEURS ---
220----->  Votre IP : x.x.x.x
220----->  Vous etes 1 connectes
220----->  TotaL Users Logged In : 6 Users
220-
220-                     ---=   RESPECT THIS STUFF  ---

We cleaned up all of these machines and rebuilt each of them from
scratch, with all the latest patches. The IDS/IPS at the edge of our
network, does not seem to be catching the bots which are causing
these.
After one week, I have 50 machines which are compromised by the same
bot, and some of them are the same as the previous list of machines.
Now  a host-based firewall is a very tough option for us, since we are
a university with around 30,000 computers and under different
departments. Does anyone know what bots are causing these and any IDS
signatures for these. We are using a couple of IDS such as snort and
Dragon and Intrushield, Any help for this is appreciated.
 I did have a look at one of these
machines and from what I see, there are a couple of files which seem
to be causing this.
there is a csmss.exe file which is listening on the port 6544.. The
machine is also running a remote server.
before csmss.exe, a file ServNT.exe seems to have been executed, which
might have caused a sequence of events.. there is a batch file , which
using the registry runs a remote admin server at startup. then we got
a number of files which are used to show the banner, hide the files .
If I could find out how did they get inside the system, because most
of the infected machines were running fully patched Windows XP with
latest Norton Antivirus definitions.?
All of those machines are running either Windows 2000 professional or
XP professional.
2 machines wer analysed, one of which was completely ptched and had
all the latest virus definitions from Norton,  another machine was not
patched and no virus updates were present.. But the state of affairs
at both the machines was the same..  themessage sent before contains
the details..
 on more analysis, I found csmss.exeto be a part of W32.Dedler
Trojan.. but how it got inside the system is anyone's guess..

None of them was running IIS.



-- 
Regards,
   Varun
   (704)-548-8793 --(Home)
   (704)-241-0092 --(Mobile)
   mailto: varun.pitale_(at)_gmail_(dot)_com