Re: What do I need to configure in snort.conf to protect against segmentation attacks?

[Gmail Personal <mainmen1985 () gmail com>]

I should also add I changed the port targeted to 22, just in case something was going weird. And I have added the port 
to the Stream5 option

Weird!

Emeka Agu | Sent from  iPad

On 26 Aug 2012, at 11:30, Emeka Agu <mainmen1985 () gmail com> wrote:

> Hi Tony thanks for the help. Still get the problem!
>
> I followed this guide too: 
> http://searchsecuritychannel.techtarget.com/tip/Snorts-Stream5-and-TCP-overlapping-fragments where Richard did 
> exactly the same thing as me
>
> And edited my Stream5 TCP policy to include the reassembly Port, but it still didn't detect anything. Surely 
> something is wrong, or is Snort that easily beaten by segmented TCP streams?
>
> Thanks
>
> On 23 August 2012 18:27, Tony Robinson <deusexmachina667 () gmail com> wrote:
> I'd check your frag3 and stream 5 settings in snort.conf, verify that stream5 is enabled and that TCP streams are 
> being assembled. according to the snort manual, stream reassembly for port 80 from client operating systems is a 
> default setting in snort.conf -- Double check that, maybe set port 80 to both. Additionally, look into the 
> stream_assembly rule option, and integrate it into your rule to ensure that TCP streams are being reassembled.
>
> http://manual.snort.org/node33.html#SECTION004621000000000000000
>
> In regards to ip fragmentation, try changing frag3 back to the defaults and see what happens.
>
> Try running a packet capture (i.e. use snort, wireshark, tshark or tcpdump) and get a pcap on the interface snort is 
> listening on to ensure the traffic is being dropped/modified somewhere in transit -- you need to verify what your 
> snort sensor is seeing.
>
> Hope this helps,
>
> -Tony
>
> On Thu, Aug 23, 2012 at 2:55 AM, Emeka Agu <mainmen1985 () gmail com> wrote:
> Hi there, I've created some code in Scapy to create a successful 3WH and then push a segmented keyword (/root/hacked) 
> over 3 packets.
>
> I also created these three rules in snort (I know the rule with no flow direction set is pointless, but I needed it 
> to confirm my findings)
>
> 1) alert tcp any any -> $HOME_NET  80 (msg:”Testing TCP”; content:”/root/hacked”; nocase; sid:11112;)
>
>  
>
> 2) alert ip any any -> $HOME_NET  80 (msg:”Testing IP Frag”; content:”/root/hacked”; nocase; sid:11113;)
>
>  
>
> 3) alert tcp any any -> $HOME_NET  80 (msg:”Testing TCP Flow”; flow:to_server, established; content:”/root/hacked”; 
> nocase; sid:11114;)
>
>
>
> But none of them are alerted when I send the packets. Wireshark manages to see the packets and when I select Follow 
> TCP Stream, and it displays the content in full. 
>
>
>
> IP tables has been turned off too I tested with an earlier evasion attempt just using a fragmented packet where it 
> split the keyword into "/roo" and "t/hacked" and  Snort detected it. I used exactly the same destination and source 
> ports, same IP source and destination, too.
>
>
>
> So I am presuming it's something to do with my snort.conf file. I've left most of the options as default, I just 
> changed the policies to linux, as I am using Backtrack as the Snort IDS
>
>
>
> Can anyone give me any guidance please?
>
>
> Cheers,
>
>
>
> Emeka
>
>
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