OT: Rapid Reset attacks on HTTP/2

[Maxim Dounin]

Hello!

On Tue, Oct 10, 2023 at 05:30:52PM -0400, Rick Gutierrez wrote:

> In the open version 1.24 and 1.25 the correction will be applied?, ¿or in
> the new release?

To re-iterate:

We do not consider nginx to be affected by this issue.  In the 
default configuration, nginx is sufficiently protected by the 
limit of allowed requests per connection (see 
http://nginx.org/r/keepalive_requests for details), so an attacker 
will be required to reconnect very often, making the attack 
obvious and easy to stop at the network level.  And it is not 
possible to circumvent the max concurrent streams limit in nginx, 
as nginx only allows additional streams when previous streams are 
completely closed.

Further, additional protection can be implemented in nginx by 
using the "limit_req" directive, which limits the rate of requests 
and rejects excessive requests.

Overall, with the handling as implemented in nginx, impact of 
streams being reset does no seem to be significantly different 
from impacts from over workloads with large number of requests 
being sent by the client, such as handling of multiple HTTP/2 
requests or HTTP/1.x pipelined requests.

Nevertheless, we've decided to implemented some additional 
mitigations which will help nginx to detect such attacks and drop 
connections with misbehaving clients faster.  The patch to do so 
was committed (http://hg.nginx.org/nginx/rev/cdda286c0f1b) and 
will be available in the next nginx release.

-- 
Maxim Dounin
http://mdounin.ru/