Re: DoS attack against TCP services

[christos%zoulas.com@localhost (Christos Zoulas)]

On Feb 4,  7:44pm, 6bone%6bone.informatik.uni-leipzig.de@localhost (6bone%6bone.informatik.uni-leipzig.de@localhost) wrote:
-- Subject: Re: DoS attack against TCP services

| Now the server has over 5000 TIME_WAIT connections.
| 
| netstat -a -n | grep TIME_WAIT
| tcp        0      0  139.18.25.33.59256     198.6.1.83.53          TIME_WAIT
| tcp        0      0  139.18.25.33.59257     77.222.50.250.53       TIME_WAIT
| tcp        0      0  139.18.25.33.59258     193.232.128.6.53       TIME_WAIT
| tcp        0      0  139.18.25.33.59259     78.104.145.37.53       TIME_WAIT
| tcp        0      0  139.18.25.33.59260     192.5.6.30.53          TIME_WAIT
| tcp        0      0  139.18.25.33.59261     192.41.162.30.53       TIME_WAIT
| tcp        0      0  139.18.25.33.59262     192.35.51.30.53        TIME_WAIT
| tcp        0      0  139.18.25.33.59263     192.43.172.30.53       TIME_WAIT
| tcp        0      0  139.18.25.33.59264     202.12.27.33.53        TIME_WAIT
| ...
| 
| It seems to be a result of the named. lsof shows that the connections are 
| not owned by named. lsof doesn't show any of the TIME_WAIT connections. So 
| stopping and restarting named doesn't delete the connections.
| 
| Any more things that could be interessing for a problem report?

I'd start a tcpdump to record all traffic from your local machine going to port
53 on the appropriate interface...

I'd also look at the open descriptors of the named process (although they
should be closed at this time, since TIME_WAIT means closed on this side,
and waiting for the 4 minutes to expire before killing the connection)...

Also I'd record that information every minute or so to see how many
connections are added and how many are going away.

Perhaps there is some bug triggered in the tcp stack and somehow connections
are not being GC'ed?

christos