[Snort-users] Very high amount of "TCP Small Segment Threshold Exceeded"

Russ Combs rcombs at ...1935...
Tue Feb 28 15:00:02 EST 2012


On Tue, Feb 28, 2012 at 2:52 PM, waldo kitty <wkitty42 at ...14940...>wrote:

> On 2/27/2012 03:39, Giacomo wrote:
> > Hi there,
> >
> > I recently started using Snort. After enabling the (default)
> preprocessor configuration I started receiving very large amounts of events
> regarding stream5.
> > Since it is a server that is not being used for anything I assume this
> event is generated by my SSH connection. A couple of topics have discussed
> this but none come with a very clear answer why this is occurring and how
> you can solve it.
> > The only two suggestions I found was to change the max_tcp value in
> stream5_global or increase the memcap. But both of these suggestions don't
> work. So I am wondering if any one of you has an idea why this is occurring
> and what I can do about it.
>
> what, exactly, are the SIDs being reported? the items you saw are for one
> or two
> things but stream5 can alert on numerous items...
>
> here's what the snort-2.9.2.1's README.stream5 has to say...
>
> Alerts
> ======
> Stream5 uses generator ID 129. It is capable of alerting on 10 anomalies,
> all of
> which relate to TCP anomalies. There are no anomaly detection capabilities
> for
> UDP or ICMP.
>
> SID   Description
> ---   -----------
> 1     SYN on established session
> 2     Data on SYN packet
> 3     Data sent on stream not accepting data
> 4     TCP Timestamp is outside of PAWS window
> 5     Bad segment, overlap adjusted size less than/equal 0
> 6     Window size (after scaling) larger than policy allows
> 7     Limit on number of overlapping TCP packets reached
> 8     Data after Reset packet
> 9     Possible Hijacked Client
> 10    Possible Hijacked Server
> 11    TCP packet with any control flags set
> 12    Limit on number of consecutive small segments reached
> 13    4-way handshake detected
> 14    Packet missing timestamp
>
>
> [ yes, there's a typo up there where it says 10 anomalies and then shows
> 14 of
> them ;) ]
>

It's actually more than that:

$ grep "^129" ../etc/gen-msg.map
129 || 1 || stream5: SYN on established session
129 || 2 || stream5: Data on SYN packet
129 || 3 || stream5: Data sent on stream not accepting data
129 || 4 || stream5: TCP Timestamp is outside of PAWS window
129 || 5 || stream5: Bad segment, overlap adjusted size less than/equal 0
129 || 6 || stream5: Window size (after scaling) larger than policy allows
129 || 7 || stream5: Limit on number of overlapping TCP packets reached
129 || 8 || stream5: Data sent on stream after TCP Reset
129 || 9 || stream5: TCP Client possibly hijacked, different Ethernet
Address
129 || 10 || stream5: TCP Server possibly hijacked, different Ethernet
Address
129 || 11 || stream5: TCP Data with no TCP Flags set
129 || 12 || stream5: TCP Small Segment Threshold Exceeded
129 || 13 || stream5: TCP 4-way handshake detected
129 || 14 || stream5: TCP Timestamp is missing
129 || 15 || stream5: Reset outside window
129 || 16 || stream5: FIN number is greater than prior FIN
129 || 17 || stream5: ACK number is greater than prior FIN
129 || 18 || stream5: Data sent on stream after TCP Reset received
129 || 19 || stream5: TCP window closed before receiving data


>
>
> ------------------------------------------------------------------------------
> Keep Your Developer Skills Current with LearnDevNow!
> The most comprehensive online learning library for Microsoft developers
> is just $99.99! Visual Studio, SharePoint, SQL - plus HTML5, CSS3, MVC3,
> Metro Style Apps, more. Free future releases when you subscribe now!
> http://p.sf.net/sfu/learndevnow-d2d
> _______________________________________________
> Snort-users mailing list
> Snort-users at lists.sourceforge.net
> Go to this URL to change user options or unsubscribe:
> https://lists.sourceforge.net/lists/listinfo/snort-users
> Snort-users list archive:
> http://www.geocrawler.com/redir-sf.php3?list=snort-users
>
> Please visit http://blog.snort.org to stay current on all the latest
> Snort news!
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.snort.org/pipermail/snort-users/attachments/20120228/e8a801f7/attachment.html>


More information about the Snort-users mailing list