RE: Should I be concerned about?

From: Lance Spitzner (lanceat_private)
Date: Wed Oct 31 2001 - 10:43:04 PST

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    On Wed, 31 Oct 2001, Mike Gilles wrote:
    
    > For any data to actually be transferred the packets would have to move up
    > the OSI model.  (e.g. start a TCP session) So, in short, no I wouldn't be
    > overly concerned with this traffic.
    
    *sigh*
    
    I'm afraid you have just fallen victim to one of the most common
    problems within the security community, underestimating the
    enemy.  Anything is possible.
    
                 http://www.phrack.org/show.php?p=51&a=6
    
    
    
    > -----Original Message-----
    > From: faial@rio-de-janeiro.sns.slb.com
    >
    > 	Today morning I start receiving a lot of ICMP packets from a host,
    > apparently in China (if the source address was not spoffed). The first
    > packet was:
    >
    > [2001-10-31 11:52:25]  ICMP Destination Unreachable (Port Unreachable)
    > IPv4: 203.193.63.9 -> XXX.XXX.XXX.XXX
    > hlen=5 TOS=192 dlen=56 ID=37607 flags=0 offset=0 TTL=235 chksum=27228
    > ICMP: type=Destination Unreachable code=Port Unreachable
    > checksum=39472 id= seq=
    > Payload:  length = 32
    > 000 : 00 00 00 00 45 00 00 4E F2 FE 00 00 68 11 8D DF   ....E..N....h...
    > 010 : A3 BA 23 3C CB C1 3F 09 00 89 00 89 00 3A 61 80   ..#<..?......:a.
    >
    > 	following thousands of packets like this:
    >
    > [2001-10-31 12:42:10]  ICMP Time-To-Live Exceeded in Transit
    > IPv4: 203.193.63.9 -> XXX.XXX.XXX.XXX
    > hlen=5 TOS=192 dlen=56 ID=49325 flags=0 offset=0 TTL=235 chksum=15510
    > ICMP: type=Time Exceeded code=0
    > checksum=48251 id= seq=
    > Payload:  length = 32
    > 000 : 00 00 00 00 45 00 00 74 4A A4 00 00 01 11 9D 13   ....E..tJ.......
    > 010 : A3 BA 23 3C CB C1 3F 0A 01 03 01 03 00 60 36 1E   ..#<..?......`6.
    >
    > I know that this can be just legitimate ICMP traffic, but I have a bad
    > felling about this activity. I am sure that the target machine never tried
    > to connect to or to send any kind of packet to the 203.193.63.9 machine, so
    > ICMP Time-To-Live would not be expected. They are "unsolicited" packets.
    >
    > My question is "Can a hacker forge an ICMP packet to bypass the firewall
    > and use its payload (payload data is different for each packet received) to
    > send data to a trojan (listening for ICMP traffic on the target machine)? "
    
    
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