Syn flood to TCP port 21 from priveleged port (80)

Christian Kildau lists at chrisk.de
Wed Nov 2 08:46:45 UTC 2016


There is some nice research regarding systems "abusable" for reflection by
tcp port and the amplification factor depending on the OS:
http://www.christian-rossow.de/publications/tcpamplification-woot2014.pdf

And in more detail:
https://www.usenix.org/system/files/conference/usenixsecurity14/sec14-paper-
kuhrer.pdf

Best regards,
Chris

On Tue, Nov 1, 2016 at 11:21 PM, Ken Chase <math at sizone.org> wrote:

> what's the density of open port 21s on the planet though? trying to
> estimate
> the traffic resulting against the two target /21s.
>
> Your dump only has 2 ip's in it though, on your /19 so not representative.
>
> My dump is 500 synacks returned in 14 seconds to 32 ips in a /22. This
> would give
> 128M ftp responders across the whole /0 (modulo actual space in use, etc,
> so call it 32M responders?). (It's also a short timespan for a dump as
> well.)
> Syn-ack seems to be a 58 byte packet (?ish).
>
> 32 * 10^6 * 500/14 * 58*8 / 10^9 = 530 Gbps
>
> even if im off by 4 in density of ftp sites on the internet despite my
> already
> reducing it by 4, we're talking ~100+ Gbps.
>
> /kc
>
>
> On Tue, Nov 01, 2016 at 03:59:49PM -0600, Selphie Keller said:
>   >Yeah it is an odd ball attack for sure, here is a 5000 packet sample of
>   >what I was seeing in connection to this attack
>   >https://mystagic.io/80to21.pcap , don't think it's the entire /0 for
> ftp
>   >port as I am not seeing it on many other subnets, which is why I am
>   >thinking someone did a pre-scan before conducting this wacky attack,
>   >otherwise, I would have likely seen other port 21's seeing activity,
> but so
>   >far any IP that didn't have 21 as an actual service isn't seeing the syn
>   >packets. This could be unique to my location, others observing this
> attack
>   >may be able to chime in and report what they are seeing if they seen 80
> src
>   >syn to port 21 where 21 isn't an actual ftp running. Yeah this is pretty
>   >easy to filter.
>   >
>   >On 1 November 2016 at 13:48, Ken Chase <math at sizone.org> wrote:
>   >
>   >> Not sure why reflected RSTs are the goal here, they're not much of an
>   >> amplification
>   >> to the original syn size. Additionally causing a mild dos of my
> clients'
>   >> stuff
>   >> when it begins throttling # of connections, ie noticeable. (not that i
>   >> want to
>   >> help scriptkids improve their attacks...). Im guessing port 80 was
> chosen
>   >> for improved
>   >> fw piercing.
>   >>
>   >> Sure is widespread though, 5 clients on very different networks all
> seeing
>   >> similar
>   >> saturation. Someone has a nice complete prescanned list of open ftps
> for
>   >> the
>   >> entire internet out there (or are they just saturating the whole /0?)
>   >>
>   >> Easy to filter though:
>   >>
>   >> tcp and src port 80 and src net '(141.138.128.0/21 or 95.131.184.0/21
> )'
>   >> and dst port 21
>   >>
>   >> Adapt for your fw rules of choice.
>   >>
>   >> /kc
>   >>
>   >>
>   >> On Tue, Nov 01, 2016 at 07:39:40PM +0000, Van Dyk, Donovan said:
>   >>   >I think Ken has nailed it. I think the source addresses are
> spoofed so
>   >> you reflect the connection (tcp syn ack) to those source addresses.
> Get
>   >> enough of those connections and the server is dead.
>   >>   >
>   >>   >Since your port 21 is open
>   >>   >
>   >>   >telnet 109.72.248.114 21
>   >>   >Trying 109.72.248.114...
>   >>   >Connected to 109.72.248.114.
>   >>   >Escape character is '^]'.
>   >>   >
>   >>   >Your address was probably scanned and saw it could be used in the
>   >> attack.
>   >>   >
>   >>   >Regards
>   >>   >--
>   >>   >Donovan Van Dyk
>   >>   >
>   >>   >SOC Network Engineer
>   >>   >
>   >>   >Office: +1.954.620.6002 x911
>   >>   >
>   >>   >Fort Lauderdale, FL USA
>   >>   >
>   >>   >
>   >>   >
>   >>   >
>   >>   >The information contained in this electronic mail transmission and
> its
>   >> attachments may be privileged and confidential and protected from
>   >> disclosure. If the reader of this message is not the intended
> recipient (or
>   >> an individual responsible for delivery of the message to such
> person), you
>   >> are strictly prohibited from copying, disseminating or distributing
> this
>   >> communication. If you have received this communication in error,
> please
>   >> notify the sender immediately and destroy all electronic, paper or
> other
>   >> versions.
>   >>   >
>   >>   >
>   >>   >On 11/1/16, 3:29 PM, "Ken Chase" <math at sizone.org> wrote:
>   >>   >
>   >>   >    seeing an awful lot of port 80 hitting port 21. (Why would
> port 80
>   >>   >    ever be used as source?). Also saw a buncha cpanel "FAILED:
> FTP"
>   >> alerts flickering
>   >>   >    on and off as the service throttled itself at a couple client
> sites
>   >> I manage.
>   >>   >
>   >>   >    I see 540 unique source IPs hitting 32 destinations on my
> network
>   >> in just 1000
>   >>   >    packets dumped on one router.
>   >>   >
>   >>   >    All from multiple sequential registered /24s in whois, but all
> from
>   >> one
>   >>   >    management company:
>   >>   >
>   >>   >    141.138.128.0/21 and 95.131.184.0/21
>   >>   >
>   >>   >    role:           William Hill Network Services
>   >>   >    abuse-mailbox:  networkservices at williamhill.co.uk
>   >>   >    address:        Infrastructure Services 2 City Walk Sweet
> Street
>   >> Leeds LS11 9AR
>   >>   >
>   >>   >    AS49061
>   >>   >
>   >>   >    course, synfloods can be spoofed... perhaps they're hoping for
> a
>   >> retaliation
>   >>   >    against WHNS.
>   >>   >
>   >>   >    /kc
>   >>   >
>   >>   >    On Tue, Nov 01, 2016 at 09:44:23PM +0300, Oleg A. Arkhangelsky
> said:
>   >>   >      >Hello,
>   >>   >      >
>   >>   >      >A couple of cuts from tcpdump output:
>   >>   >      >
>   >>   >      >21:31:54.995170 IP 141.138.131.115.80 > 109.72.248.114.21:
> Flags
>   >> [S], seq 1376379765, win 8192, length 0
>   >>   >      >21:31:55.231925 IP 194.73.173.154.80 > 109.72.241.198.21:
> Flags
>   >> [S], seq 2254756684, win 8192, length 0
>   >>   >      >21:27:50.413927 IP 95.131.188.179.80 > 109.72.248.114.21:
> Flags
>   >> [S], seq 3619475318, win 8192, length 0
>   >>   >      >21:27:50.477014 IP 95.131.191.77.80 > 109.72.248.114.21:
> Flags
>   >> [S], seq 2412690982, win 8192, length 0
>   >>   >      >
>   >>   >      >Does anyone seeing this right now (18:31 UTC)? I see this
> traffic
>   >>   >      >on at least two completely independent ISPs near Moscow. The
>   >>   >      >rate is about a few dozen PPS hitting all BGP-announced
> networks.
>   >>   >      >
>   >>   >      >--??
>   >>   >      >wbr, Oleg.
>   >>   >      >
>   >>   >      >"Anarchy is about taking complete responsibility for
> yourself."
>   >>   >      >?? ?? ?? Alan Moore.
>   >>   >
>
> --
> Ken Chase - math at sizone.org Guelph Canada
>


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