Subject: Re: [bitcoindev] A Free-Relay Attack Exploiting RBF Rule #6

From: Peter Todd <[email-masked]>
Date: Thu, 28 Mar 2024 19:16:22 +0000

On Thu, Mar 28, 2024 at 06:34:42PM +0000, Antoine Riard wrote:
> Hi Steve,
> 
> > He literally cites a reference to an example.
> 
> About CVE-2017-12842,  the report of Sergio Demian Lerner available here
> gives more information on the reporting process of the vulnerability:
> https://bitslog.com/2018/06/09/leaf-node-weakness-in-bitcoin-merkle-tree-design/
> 
> I'll attract attention on the following words of Sergio himself:
> 
> "and as I said in the first paragraph, the weakness was already known by
> some developers. But I still don't understand (1) why so many people knew
> about it but underestimated it badly, (2) why there was no attempt to fix
> it."

I do not consider CVE-2017-12842 to be serious. Indeed, I'm skeptical that we
should even fix it with a fork. SPV validation is very sketchy, and the amount
of work and money required to trigger CVE-2017-12842 is probably as or more
expensive than simply creating fake blocks.

Sergio's RSK Bridge contract being vulnerable to it just indicates it was a
reckless design.

> I believe in the present "free-relay" bandwidth wasting, letting a minimal
> 2-weeks delay would have been more reasonable. Security list members might
> be in flight travels or at conferences, or under other operational
> constraints and domain experts in the area of transaction-relay might not
> be available to give full-fledged answers. Even if you have private
> contacts of someone, don't rush them to get an answer when it can be
> midnight in their time zones and they're recovering from jet lags.

To be clear, in this particular case I had specific, insider, knowledge that
the relevant people had in fact seen my report and had already decided to
dismiss it. This isn't a typical case where you're emailing some random company
and don't have any contacts. I personally knew prior to publication that the
relevant people had been given a fair chance to comment, had chosen not to, and
I would likely receive no response at all. Which is really annoying as I have
my own deadlines for (paid) things this research was relevant to: much more
useful to me to get the issue published publicly, so I can get actual comments
from people like yourself, and move forward with my work.

I'm not going to say anything further on how I knew this, because I'm not about
to put up people who have been co-operating with me to the risk of harassment
from people like Harding and others; I'm not very popular right now with many
of the Bitcoin Core people working on the mempool code.

Anyway, I think the lesson learned here is it's probably not worth bothering
with a disclosure process at all for this type of issue. It just created a
bunch of distracting political drama when simply publishing this exploit
variation immediately probably would not have.

-- 
https://petertodd.org 'peter'[:-1]@petertodd.org

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