Re: Security Guideance

["LaDerrick H." <nanog () lacutt com>]

On Tue, Feb 23, 2010 at 02:46:54PM -0500, Paul Stewart wrote:
> Hi folks...
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> We have a strange series of events going on in the past while.... Brief
> history here, looking for input from the community - especially some of
> the security folks on here.
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> We provide web hosting services - one of our hosting boxes was found a
> while back with root kits installed, un patched software and lots of
> other "goodies".    With some staff changes in place (don't think I need
> to elaborate on that) we are trying to clean up several issues including
> this particular server.  A new server was provisioned, patched, and
> deployed.  User data was moved over and now the same issue is coming
> back....
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> The problem is that a user on this box appears to be launching high
> traffic DOS attacks from it towards other sites.  These are UDP based
> floods that move around from time to time - most of these attacks only
> last a few minutes.

Counting outbound udp bytes and packets can help spot anomalies.
Something like this would help but may be unwieldy if you have thousands
of users on a single box:

WANIF=eth0
userlist="userA userB user..."
for i in ${userlist}
do
   iptables -N ${i}_UDP
   iptables -I OUTPUT -m owner -o ${WANIF} -p udp --uid-owner ${i} -j ${i}_UDP
done

Then look at counters with:
iptables -nvL OUTPUT | grep _UDP | sort.......

I wouldn't leave this in place full-time for thousands of accounts
though without attempting to measure the impact on network performance.

> I've done tcpdumps within seconds of the attack starting and to date
> been unable to find the source of this attack (we know the server,
> just not sure which customer it is on the server that's been
> compromised).  Several hours of scanning for php, cgi, pl type files
> have been wasted and come up nowhere...
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> It's been suggested to dump IDS in front of this box and I know I'll
> get some feedback positive and negative in that aspect.
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> What tools/practices do others use to resolve this issue?  It's  a
> Centos 5.4 box running latest Plesk control panel.
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> Typically we have found it easy to track down the offending script or
> program - this time hasn't been easy at all...
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> Thanks,
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> Paul
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