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Re: [Emerging-Sigs] TCP/UDP "trivial" ports?
From: "Castle, Shane" <scastle () bouldercounty org>
Date: Tue, 23 Apr 2013 19:38:45 +0000

To follow up, after some investigating (never assume) I see that I am not doing the job of blocking these that I 
thought I was doing. I even had to add some to the firewall's list of known ports.

In general, it appears that ports 7, 9, 11, 13, 15, 17, 18, and 19 fall into this area (18 is actually message send 
protocol and is used in older Unix "message" commands). I suppose that it might be possible to create rules that are 
for each protocol or for the entire range (make it 1-19 maybe, both for TCP and for UDP).

Why would this be expensive? No digging beyond the protocol headers need occur I'd think. Could a preprocessor be built 
instead, if it's expensive?

-- 
Shane Castle
Data Security Mgr, Boulder County IT


-----Original Message-----
From: Will Metcalf [mailto:william.metcalf () gmail com] 
Sent: Tuesday, April 23, 2013 13:29
To: Castle, Shane
Cc: emerging-sigs () lists emergingthreats net; snort-sigs () lists sourceforge net
Subject: Re: [Emerging-Sigs] TCP/UDP "trivial" ports?

UDP sig with threshold might be interesting... Will be expensive though. What do yo guy's think?


Regards,

Will



On Tue, Apr 23, 2013 at 1:35 PM, Castle, Shane <scastle () bouldercounty org> wrote:


        I see that using the chargen port for DDoS is happening: 
https://isc.sans.edu/diary/A+Chargen-based+DDoS+Chargen+is+still+a+thing+/15647
        
        Now, I block all these both ways at my firewall (actually, on the outside, I think they are in a router ACL), 
but looking through the complete set of rules I don't see anything but one ("DOS UDP echo+chargen bomb",sid 271) that 
seems to address this port range of the TCP and UDP "trivial" (AKA "simple") ports. Has there ever been one? Should we 
have one?
        
        --
        Shane Castle
        Data Security Mgr, Boulder County IT
        
        
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