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

Tue Nov 1 22:21:26 UTC 2016

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