Re: port scan to juniper fw

[aditya mukadam <aditya.mukadam () gmail com>]

Its good to know that the issue is resolved. However,please also note
the below default behavior of Juniper SSG for a port scan.

The security device internally logs the number of different ports
scanned from one remote source. Using the default settings, if a
remote host scans 10 ports in 0.005 seconds (5000 microseconds), the
device flags this as a port scan attack, and rejects all further
packets from the remote source for
the remainder of the specified timeout period. The device detects and drops the
tenth packet that meets the port scan attack criterion.

Thanks,
Aditya Govind Mukadam

On Wed, Oct 21, 2009 at 11:17 PM, raimarm () gmail com
<raimarm () googlemail com> wrote:
> Hi All,
>
> thank you very much for your answers and advices.
> Deactivating the syn-proxy solved the issue.
>
> Many Thanks
> rm
>
> 2009/10/20 Paul Melson <pmelson () gmail com>:
> > On Sun, Oct 18, 2009 at 8:15 AM, raimarm () gmail com
> > <raimarm () googlemail com> wrote:
> > > Dear list,
> > > I am performing a port scan to an IP address of juniper SSG firewall (6.2.r3).
> > > When the port scan finishes the results show me a lot of open ports
> > > although they are not open.
> > > Further the results differ and the same scan shows different open
> > > ports next time.
> > > The tcpdump during the port scan shows me that the fw is answering
> > > with a syn-ack after the third syn.
> > > Why is this happening ? I would expect no answer or a rst packet.
> >
> > This is the result of the Juniper firewall having SYN flood protection
> > mode being enabled.  This causes the firewall to begin responding to
> > SYN packets with SYN-ACK once the flood threshold is reached.  There
> > are two modes, syn-proxy and syn-cookie.  This is intended to protect
> > slow/unresponsive servers behind the firewall as well as the firewall
> > itself.  Y
> >
> > https://support.neoteris.com/products/integrated/dos.pdf
> >
> > ou can detect which is being used by capturing the traffic from your
> > portscan using tcpdump or Wireshark and examining the SYN+ACK packets
> > from the firewall.  If the ISNs are random, then the firewall is using
> > syn-proxy mode.  If the ISNs incrementally by port number (and then
> > again by time every 64s) then syn-cookie mode is enabled.  This might
> > be an interesting finding to share with your client.  Or not.  If they
> > are using syn-proxy mode, you can recommend that they use syn-cookie
> > mode since it's less CPU and memory intensive for the firewall.
> >
> > For the purposes of your test, you could ask your client to disable
> > this feature temporarily while you scan, but advise them that it could
> > leave older, slower servers vulnerable to a DoS attack.  Or you could
> > simply ask them to share a copy of the firewall configuration in order
> > to speed up the pen-test.  If neither of these is an option, you could
> > try a FIN scan or a Version (-sV) scan to try and reduce the false
> > open port findings.  Either way, I would go back to the client and
> > communicate the issue you're having so that they understand the delay.
> >  Port scanning always sounds like the easiest part of a pen-test, but
> > often it's the hardest.
> >
> > PaulM
>
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Prove to peers and potential employers without a doubt that you can actually do a proper penetration test. IACRB CPT 
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