[bitcoin-dev] CVE-2018-17144 disclosure (inflation vulnerability) (copy-paste)

[Bryan Bishop]

It has been informed to me that the writeup for the recent
vulnerability was not distributed to this mailing list. Please find
details at the following blog post:

https://bitcoincore.org/en/2018/09/20/notice/

I believe a release notice was posted but not information about the bug,
https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2018-September/016413.html
https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2018-September/016414.html

There was also further discussion here:
https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2018-September/016424.html

Also, around the time those emails were sent, there was a mailing list
moderator queue bug and nobody was able to approve emails including
myself. This bug was subsequently resolved by Linux Foundation.

The remainder of this email is copy-paste from the bitcoincore.org
page linked above.

=== Full disclosure ===

CVE-2018-17144, a fix for which was released on September 18th in
Bitcoin Core versions 0.16.3 and 0.17.0rc4, includes both a Denial of
Service component and a critical inflation vulnerability. It was
originally reported to several developers working on Bitcoin Core, as
well as projects supporting other cryptocurrencies, including ABC and
Unlimited on September 17th as a Denial of Service bug only, however
we quickly determined that the issue was also an inflation
vulnerability with the same root cause and fix.

In order to encourage rapid upgrades, the decision was made to
immediately patch and disclose the less serious Denial of Service
vulnerability, concurrently with reaching out to miners, businesses,
and other affected systems while delaying publication of the full
issue to give times for systems to upgrade. On September 20th a post
in a public forum reported the full impact and although it was quickly
retracted the claim was further circulated.

At this time we believe over half of the Bitcoin hashrate has upgraded
to patched nodes. We are unaware of any attempts to exploit this
vulnerability.

However, it still remains critical that affected users upgrade and
apply the latest patches to ensure no possibility of large
reorganizations, mining of invalid blocks, or acceptance of invalid
transactions occurs.

=== Technical details ===

In Bitcoin Core 0.14, an optimization was added (Bitcoin Core PR
#9049) which avoided a costly check during initial pre-relay block
validation that multiple inputs within a single transaction did not
spend the same input twice which was added in 2012 (PR #443). While
the UTXO-updating logic has sufficient knowledge to check that such a
condition is not violated in 0.14 it only did so in a sanity check
assertion and not with full error handling (it did, however, fully
handle this case twice in prior to 0.8).

Thus, in Bitcoin Core 0.14.X, any attempts to double-spend a
transaction output within a single transaction inside of a block will
result in an assertion failure and a crash, as was originally
reported.

In Bitcoin Core 0.15, as a part of a larger redesign to simplify
unspent transaction output tracking and correct a resource exhaustion
attack the assertion was changed subtly. Instead of asserting that the
output being marked spent was previously unspent, it only asserts that
it exists.

Thus, in Bitcoin Core 0.15.X, 0.16.0, 0.16.1, and 0.16.2, any attempts
to double-spend a transaction output within a single transaction
inside of a block where the output being spent was created in the same
block, the same assertion failure will occur (as exists in the test
case which was included in the 0.16.3 patch). However, if the output
being double-spent was created in a previous block, an entry will
still remain in the CCoin map with the DIRTY flag set and having been
marked as spent, resulting in no such assertion. This could allow a
miner to inflate the supply of Bitcoin as they would be then able to
claim the value being spent twice.

=== Timeline ===

Timeline for September 17, 2018: (all times UTC)

14:57 anonymous reporter reports crash bug to: Pieter Wuille, Greg
Maxwell, Wladimir Van Der Laan of Bitcoin Core, deadalnix of Bitcoin
ABC, and sickpig of Bitcoin Unlimited.
15:15 Greg Maxwell shares the original report with Cory Fields, Suhas
Daftuar, Alex Morcos and Matt Corallo
17:47 Matt Corallo identifies inflation bug
19:15 Matt Corallo first tries to reach slushpool CEO to have a line
of communication open to apply a patch quickly
19:29 Greg Maxwell timestamps the hash of a test-case which
demonstrates the inflation vulnerability
(a47344b7dceddff6c6cc1c7e97f1588d99e6dba706011b6ccc2e615b88fe4350)
20:15 John Newbery and James O’Beirne are informed of the
vulnerability so they can assist in alerting companies to a pending
patch for a DoS vulnerability
20:30 Matt Corallo speaks with slushpool CTO and CEO and shares patch
with disclosure of the Denial of Service
20:48 slushpool confirmed upgraded
21:08 Alert was sent to Bitcoin ABC that a patch will be posted
publicly by 22:00
21:30 (approx) Responded to original reporter with an acknowledgment
21:57 Bitcoin Core PR 14247 published with patch and test
demonstrating the Denial of Service bug
21:58 Bitcoin ABC publishes their patch
22:07 Advisory email with link to Bitcoin Core PR and patch goes out
to Optech members, among others
23:21 Bitcoin Core version 0.17.0rc4 tagged

September 18, 2018:

00:24 Bitcoin Core version 0.16.3 tagged
20:44 Bitcoin Core release binaries and release announcements were available
21:47 Bitcointalk and reddit have public banners urging people to upgrade

September 19, 2018:

14:06 The mailing list distributes an additional message urging people
to upgrade by Pieter Wuille

September 20, 2018:

19:50 David Jaenson independently discovered the vulnerability, and it
was reported to the Bitcoin Core security contact email.



- Bryan
http://heybryan.org/
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