TCP-AMP DDoS Attack - Fake abuse reports problem

Fri Feb 21 11:17:21 UTC 2020

Good luck responding to such SYN/ACK, when you get 10+Gbps of them (real 
case happened while ago with colleague).
Sure those SYN/ACK are not from single location, and attackers might use 
whole /24 for SYN spoofing.

On 2020-02-21 03:34, Amir Herzberg wrote:
> If I read your description correctly:
> 
> - Attacker sends spoofed TCP SYN from your IP address(es) and
> different src ports, to some TCP servers (e.g. port 80)
> - TCP servers respond with SYN/ACK  ; many servers resend the SYN/ACK
> hence amplification .
> - *** your system does not respond ***
> - Servers may think you're doing SYN-Flood against them, since
> connection remains in SYN_RCVD, and hence complain. In fact, we don't
> really know what is the goal of the attackers; they may in fact be
> trying to do SYN-Flood against these servers, and you're just a
> secondary victim and not the even the target, that's also possible.
> 
> Anyway, is this the case?
> 
> If it is... may I ask, do you (or why don't you) respond to the
> unsolicited SYN/ACK with RST as per the RFC?
> 
> I suspect you don't, maybe due to these packets being dropped by
> FW/NAT, that's quite common. But as you should understand by now from
> my text, this (non-standard) behavior is NOT recommended. The problem
> may disappear if you reconfigure your FW/NAT (or host) to respond with
> RST to unsolicited SYN/ACK.
> 
> As I explained above, if my conjectures are true, then OVH as well as
> the remote servers may have a valid reason to consider you either as
> the attacker or as an (unknowning, perhaps) accomplice.
> 
> I may be wrong - sorry if so - and would appreciate, in any case, if
> you can confirm or clarify, thanks.
> 
> --
> Amir Herzberg
> 
> Comcast professor of Security Innovations, University of Connecticut
> 
> Homepage: https://sites.google.com/site/amirherzberg/home
> 
> Foundations of Cyber-Security (part I: applied crypto, part II:
> network-security):
> https://www.researchgate.net/project/Foundations-of-Cyber-Security
> 
> On Thu, Feb 20, 2020 at 5:23 PM Octolus Development
> <admin at octolus.net> wrote:
> 
>> A very old attack method called TCP-AMP (
>> https://pastebin.com/jYhWdgHn ) has been getting really popular
>> recently.
>> 
>> I've been a victim of it multiple times on many of my IP's and every
>> time it happens - My IP's end up getting blacklisted in major big
>> databases. We also receive tons of abuse reports for "Port
>> Scanning".
>> 
>> Example of the reports we're getting:
>> 
>> tcp: 51.81.XX.XX:19342 -> 209.208.XX.XX:80 (SYN_RECV)
>> tcp: 51.81.XX.XX:14066 -> 209.208.XX.XX:80 (SYN_RECV)
>> 
>> OVH are threatening to kick us off their network, because we are
>> victims of this attack. And requesting us to do something about it,
>> despite the fact that there is nothing you can do when you are being
>> victim of an DDoS Attack.
>> 
>> Anyone else had any problems with these kind of attacks?
>> 
>> The attack basically works like this;
>> - The attacker scans the internet for TCP Services, i.e port 80.
>> - The attacker then sends spoofed requests from our IP to these TCP
>> Services, which makes the remote service attempt to connect to us to
>> initiate the handshake.. This clearly fails.
>> ... Which ends up with hundreds of request to these services,
>> reporting us for "port flood".