full-disclosure - ISS 'Witty' Worm Analyzed

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From: Jean-Baptiste.Marchand at hsc.fr (Jean-Baptiste Marchand)
Subject: ISS 'Witty' Worm Analyzed

* mattmurphy@...rr.com <mattmurphy@...rr.com>:

> I have completed an analysis of the 'Witty' worm that impacts multiple ISS
> products.  The worm is spreading via a very simple UDP propagation
> algorithm.  The unique nature of this worm made it a fascinating piece of
> code to analyze.  The analysis gets into the details of the worm's
> propagation mechanism, and is designed for a more technical reader, but
> does include a basic description of the worm, and the list of products
> vulnerable to it (as published by ISS).

Very interesting document, thanks!

By the way, if people are trying to decode Witty with Ethereal
(http://www.ethereal.com/), you might be surprised not to see the same
decoding of ICQ messages as shown in Matthew's paper.

Because Witty sets the Session ID field to 00 00 00 00, the Ethereal ICQ
dissector is confused and dissects Witty messages as client-to-server
messages instead of server-to-client messages.

(extract of packet-icq.c, available on
http://www.ethereal.com/cgi-bin/viewcvs.cgi/ethereal/packet-icq.c)

 if (unknown == 0x0L) {
      dissect_icqv5Client(tvb, pinfo, tree);
  } else {
      dissect_icqv5Server(tvb, 0, pinfo, tree, -1);
  }

As presented in the following document:

http://www.cs.berkeley.edu/~mikechen/im/protocols/icq/icqv5.html

client-to-server ICQ messages start with:

2 bytes 05 00   VERSION Protocol version                                                                                                                                 
4 bytes 00 00 00 00     ZERO    Just zeros, purpouse unknown
...

and server-to-client ICQ messages start with:

2 bytes 05 00   VERSION Protocol version                                                                                                                                 
1 byte  00      ZERO    Unknown                                                                                                                                          
4 bytes xx xx xx xx     SESSION_ID      Same as in your login packet.
...

In Witty case, the SESSION_ID is set to 0 and the ethereal dissector
believes that the ICQ message is a client-to-server one.

It might be a good idea to add a test to the ethereal dissector to
determine if a given ICQ messages is a client-to-server or
server-to-client one, examining the source port (if source port is set
to 4000, it might be a good indication that this is a server-to-client
message...). I will probably propose such a modification on
ethereal-dev@.

Thus, to properly dissect Witty ICQ messages with Ethereal, you just
have to modify one of the 4 bytes that constitute the session id and set
it to 0x01 instead of 0x00.

With such a modification, Witty ICQ messages are properly decoded, as
shown in the following tethereal output:

...

ICQv5 SRV_MULTI_PACKET (len 1211)
    Header
        Version: 5
        Session ID: 0x00000004
        Command: SRV_MULTI_PACKET (530)
        Seq Number 1: 0x0000
        Seq Number 2: 0x0000
        UIN: 0
        Checkcode: 0x00000000
    Body
        Number of pkts: 2
        ICQv5 SRV_USER_ONLINE (len 44)
            Header
                Version: 5
                Session ID: 0x00000000
                Command: SRV_USER_ONLINE (110)
                Seq Number 1: 0x0000
                Seq Number 2: 0x0000
                UIN: 0
                Checkcode: 0x00000000
            Body
                UIN: 0
                IP: 1.0.0.0
                Port: 0
                RealIP: 0.0.0.0
                Status: ONLINE
                Version: 02410000
        ICQv5 SRV_META_USER (len 577)
            Header
                Version: 5
                Session ID: 0x00000000
                Command: SRV_META_USER (990)
                Seq Number 1: 0x0000
                Seq Number 2: 0x0000
                UIN: 0
                Checkcode: 0x00000000
            Unknown (0x0000)
                Failure

This corresponds exactly to the manual decoding presented in Matthew's
paper.

Jean-Baptiste Marchand
-- 
Jean-Baptiste.Marchand@....fr
HSC - http://www.hsc.fr/