Should I be concerned about?

From: Jose Carlos Faial (faial@rio-de-janeiro.sns.slb.com)
Date: Wed Oct 31 2001 - 11:05:45 PST

  • Next message: Mike Gilles: "RE: 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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