RE: Should I be concerned about?

[Mike Gilles <mike.gilles () itmtech com>]

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.

-----Original Message-----
From: faial () rio-de-janeiro sns slb com
[mailto:faial () rio-de-janeiro sns slb com]
Sent: Wednesday, October 31, 2001 2:06 PM
To: incidents () securityfocus com
Subject: Should I be concerned about?


Hi all,

        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)? "

Thanks to all.

faial 


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