TCP-AMP DDoS Attack - Fake abuse reports problem

Damian Menscher damian at google.com
Fri Feb 21 04:20:58 UTC 2020


Amir: you're exactly correct -- but since you asked, here's their answer
from the last time I suggested they respond with RSTs:
https://seclists.org/nanog/2020/Jan/612

Damian

On Thu, Feb 20, 2020 at 5:36 PM Amir Herzberg <amir.lists at gmail.com> 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".
>>
>>
>>
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