[Snort-users] Detecting DDoS attacks with Snort

Joel Esler (jesler) jesler at ...589...
Mon Jan 23 10:20:56 EST 2017


You can enable your own thresholds in the threshold.conf.


--
Joel Esler | Talos: Manager | jesler at ...589...<mailto:jesler at ...589...>






On Jan 23, 2017, at 9:54 AM, Ana Serrano Mamolar <B00315494 at ...17757...<mailto:B00315494 at ...17757...>> wrote:

Thanks for your response Joel.
I have also installed PulledPork to have more updated rules, but still don't understand why I have to get an alert per packet in a DDoS attack.
For example, following your link, I randomly selected one rule with a DoS classtype that I copied bellow. If I use scapy to send 2000 packets that  match the signature showed in this rule, Snort will trigger 2000 alerts. That's what I can not understand from the beginning. Why 2000 alerts. Shouldn't exist a kind of threshold to consider an attack or not, depending on the amount of packets received/sent?



# alert udp $EXTERNAL_NET any -> $HOME_NET 31335 (msg:"MALWARE-OTHER Trin00 Daemon to Master message detected"; flow:to_server; content:"l44"; fast_pattern:only; metadata:ruleset community; reference:cve,2000-0138; classtype:attempted-dos; sid:231; rev:11;)
________________________________
From: Joel Esler (jesler) <jesler at ...589...<mailto:jesler at ...589...>>
Sent: 23 January 2017 14:41:07
To: Ana Serrano Mamolar
Cc: snort-users at lists.sourceforge.net<mailto:snort-users at lists.sourceforge.net>
Subject: Re: [Snort-users] Detecting DDoS attacks with Snort

Those rules are six years old.  I’d suggest getting a more up to date ruleset from Snort.org<http://snort.org/>.

--
Joel Esler | Talos: Manager | jesler at ...589...<mailto:jesler at ...589...>






On Jan 23, 2017, at 5:25 AM, Ana Serrano Mamolar <B00315494 at ...17757...<mailto:B00315494 at ...17757...>> wrote:


Hi everyone,,
I am a beginner with Snort. For my research, I would like to use Snort to detect DDoS attacks.
So, what I have done is, first install Snort and download DDoS rules from here https://github.com/eldondev/Snort/blob/master/rules/ddos.rules.
Then, I tried to generate some traffic that match some of this rules to see if Snort triggered alerts. I started to use scapy and I managed to generate ICMP and UDP DoS attacks, but not TCP for the moment, and not Distributed, but just DoS. I am open also to new ideas about that issue of generating traffic to simulate my attacks ( also pcaps would be suitable).

My main worry, and the aim of this message, is that I am not sure to have understood well how Snort rules work. I don't understand why I am getting one alert per packet sent. So, if i send 2000 packets matching a rule I receive 2000 alerts. As far as I know, a DDoS attack attempt to overload systems, so one packet, is not a DoS attack.

So, does somebody know how I should do a real experiment? Maybe that rules are not good to detect an attack? Maybe I am not running Snort in the proper mode?

Thanks in advance
Ana


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