[Snort-devel] Strange behavior observed in Viruscan 8 Pro
Bedon Cortazar Charles Edward
cbedon at ...2535...
Tue Dec 6 15:04:01 EST 2005
We want to report a strange/curious behavior observed while studying the
response of sfportscan preprocessor.
A host in our network has running MCaffe Viruscan Pro 8.0 Build 8.0.20
Engine 4.2.6. It tries to update itself by making requests to
MCaffe web server at 220.127.116.11 through a proxy(yes, we
know if not configured correctly, this update never could be initiated,
but that is not the point). Each request the program tries to make, is
rejected by the proxy (Viruscan update program sends a SYN, and web server(the proxy, in
fact) seems to answer with a RST_ACK), so far, nuttin' strange. But when VS
receives that answer it uses another port and other and other ... but the result is always the
same. In Ethereal, we can see something like this (not the actual
/*Three attempts for each port, the other 2 are not listed here*/
192.0.0.1:2000 (SYN)--> 18.104.22.168:80
22.214.171.124:80 (RST_ACK)--> 192.0.0.1:2000
192.0.0.1:2001 (SYN)--> 126.96.36.199:80
188.8.131.52:80 (RST_ACK)--> 192.0.0.1:2001
192.0.0.1:2002 (SYN)--> 184.108.40.206:80
220.127.116.11:80 (RST_ACK)--> 192.0.0.1:2002
192.0.0.1:2003 (SYN)--> 18.104.22.168:80
22.214.171.124:80 (RST_ACK)--> 192.0.0.1:2003
What's the effect on Snort? well in "flow" preprocessor(first
filter for all stateful portscan preprocessors like flowportscan and
sfportscan), there is a flow
hash, which key is a combination of srcIP,srcPort,dstIP and dstPort, and
each time VScan changes the port for the update connection attempt, a new
flow is risen. sfportscan reports this as a portsweep.
We think that one approach could be removing the srcPort from the key,
for the good of the portscan detectors, since this is not a relevant
parameter for the analysis. However, this could be a problem
for the rest of preprocessors that makes use of flow_spp, if any.
Our questions are:
*Have u ever seen this behavior before?
*What do u think that could be a solution for this issue?
Faculta de Ingeniería Electrónica y Telecomunicaciones
Univeridad del Cauca
Popayán - Colombia
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