[tor-relays] Circuit Creation Madness: Anyone else still experiencing (extremely) excessive clients / (possibly) modified relays creating millions upon millions of circuits?

Roger Dingledine arma at torproject.org
Tue Mar 23 06:33:55 UTC 2021

On Mon, Mar 22, 2021 at 07:54:43PM +0000, William Kane wrote:
> Sorry for being quite noisy recently but I really need to know how
> many people are suffering from the same madness I am encountering
> right now.
> Quick excerpt from the log:
> Mar 22 09:48:10 <hostname_redacted> tor[pid_redacted]: Mar 22
> 09:48:10.000 [warn] Your computer is too slow to handle this many
> circuit creation requests! Please consider using the
> MaxAdvertisedBandwidth config option or choosing a more restricted
> exit policy. [12420 similar message(s) suppressed in last 120 seconds]

Yes, it could help to hear if many people are experiencing these log
messages or just a few.

There are several known situations where the log messages could happen to
a small subset of the relays at any given time. For example, if somebody
is trying to flood a particular onion service, then the six or eight
HSDirs for that onion address for that day could see a lot of overload
(which would last for as much as that day), and also the introduction
points listed in the descriptors could see a lot of overload (which
would last a lot less than a day probably).

> Might be smart to add some code which, if this scenario is triggered,
> lists offenders by hashes of their signing keys (if relay), or IP
> addresses (if client).

For the variants of the overloads that we've seen so far, they are
done via Tor, i.e. your relay doesn't actually know who is starting
the circuits, so those logs would be at best useless. (We built an
anonymity system, and now it keeps people anonymous. We can't be *too*
unhappy here. :)

I think the long term answer for these attacks are the options outlined
by George in this blog post:

I'm especially interested in the proof-of-work variant, which doesn't
need an interface where the human does stuff, doesn't need to be hooked
together with a global ecash system that everybody wants a piece of, etc:

But as they say, more work remains.


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