Hi to the list

We are running a new iptables firewall with
restrictives policies.

I just noticed that sometimes (between 1 an 4 packets per
weeks), our IIS 5.0 server try to send NetBIOS name
query on foreign IPs.

Here is a hex dump of that packet :

11:44:56.495348 x.x.x.x.netbios-ns > 211.40.x.y.netbios-ns: NBT UDP
PACKET(137): QUERY; REQUEST; UNICAST
0x0000 4500 004e b2bf 0000 8011 ff8f XXXX XXXX E..N.........hR.
0x0010 d328 913c 0089 0089 003a 6ff0 c7ee 0000 .(.<.....:o.....
0x0020 0001 0000 0000 0000 2043 4b41 4141 4141 .........CKAAAAA
0x0030 4141 4141 4141 4141 4141 4141 4141 4141 AAAAAAAAAAAAAAAA
0x0040 4141 4141 4141 4141 4100 0021 0001 AAAAAAAAA..!..

x.x.x.x is our server (i replaced hex dump with XXXX XXXX too)

Source : our server
Proto : UDP
Source port : 137
Dest : foreign server
Dest port : 137

I'd like to identify the source of these packets.

One thing that comes in mind is :
Would it be related to the option in IIS "reverse
lookup host" to log hostnames in the log file ?

I remember that nslookup() function of NT kernel
uses netbios if DNS doesnt reply anything
(correct me if i'm wrong).

There is not other inbound port than 80 opened.
Opened outbound ports are packets related to a already
opened connection on port 80 and DNS queries to our
servers. The server itself cannot open a connection
on Internet.

Since this server is hosting ASP & ASP.NET services,
I agree it would be possible to get access via
some crafted URLs or webapp attacks, but we didnt
see anything else than these packets.

Someone may enlighten me ?

Thanks in advance

Maxime Ducharme
Programmeur / Spécialiste en sécurité réseau

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