Re: Detecting DDoS attacks with Snort

[Ana Serrano Mamolar <B00315494 () studentmail uws ac uk>]

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 () cisco com>
Sent: 23 January 2017 14:41:07
To: Ana Serrano Mamolar
Cc: snort-users () 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 () cisco com<mailto:jesler () cisco com>






On Jan 23, 2017, at 5:25 AM, Ana Serrano Mamolar <B00315494 () studentmail uws ac uk<mailto:B00315494 () studentmail 
uws ac uk>> 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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