The typescript SDK has no awareness of to-be-spent transactions causing some transactions to fail or silently get pruned as they are funded with already used UTXOs.
The Typescript SDK
provides the fund
function which retrieves UTXOs
, which belong to the owner and can be used to fund the request in question, from fuel's graphql api. These then get added to the request making it possible to send it to the network as it now has inputs which can be spent by its outputs. Now this works when a user only wants to fund one transaction per block as in the next block, the spent UTXO will not exist anymore. However if a user wants to fund multiple transactions within one block, the following can happen:
It is important to note, that the graphql API will return a random UTXO which has enough value to fund the transaction in question.
UTXOs
in their wallet which can cover all expensestA
with an input gotten from the API iA
tA
to fueliA
is still in possession of the user as no new block has been producedtB
and gets the same input iA
from the APItB
to fuel but now one of the following can happen:
tA
, submission will fail as tB
will have the same txHash
as tA
txpool
and tA
will be removed from the txpool
The problem occurs, because the fund
function in fuels-ts/packages/account/src/account.ts
gets the needed ressources statelessly with the function getResourcesToSpend
without taking into consideration already used UTXOs:
async fund<T extends TransactionRequest>(request: T, params: EstimatedTxParams): Promise<T> {
// [...]
let missingQuantities: CoinQuantity[] = [];
Object.entries(quantitiesDict).forEach(([assetId, { owned, required }]) => {
if (owned.lt(required)) {
missingQuantities.push({
assetId,
amount: required.sub(owned),
});
}
});
let needsToBeFunded = missingQuantities.length > 0;
let fundingAttempts = 0;
while (needsToBeFunded && fundingAttempts < MAX_FUNDING_ATTEMPTS) {
const resources = await this.getResourcesToSpend(
missingQuantities,
cacheRequestInputsResourcesFromOwner(request.inputs, this.address)
); // @audit-issue here we do not exclude ids we already got and used for another transaction in the current block
request.addResources(resources);
// [...]
}
// [...]
return request;
}
This issue will lead to unexpected SDK behaviour. Looking at the scenario in Brief/Intro
, it could have the following impacts for users:
txpool
/ in a blocktxpool
and replaced with a new oneI would recommend adding a buffer to the Account
class, in which retrieved resources
are saved. These can then be provided to getResourcesToSpend
to be excluded from future queries but need to be removed from the buffer if their respective transaction fails to be included, in order to be able to use those resources
again in such cases.
The following PoC transfers 100 coins from wallet2
to wallet
after which wallet2
has two UTXOs
one with value 100
and one with a very high value (this is printed to the console). Afterwards, wallet
will attempt transfering 80
coins back to wallet2
twice in one block, each in a separate transaction. This should work perfectly fine as wallet
has two UTXOs
where each can cover the cost of each respective transaction. Now when running this one of the following will happen:
wallet
to wallet2
get a different UTXO
. This is the case if execution is successful and wallet2
has 80
coins more than wallet
in the end.UTXO
. In this case the script will fail and throw an error as then both transactions will have the same hashIn order to execute this PoC, please deploy a local node with a blocktime of 5secs
as I wrote my PoC for that blocktime. Note that with a small change it will also work with other blocktimes. Then add the PoC to a file poc_resources.ts
and compile it with tsc poc_resources.ts
. Finally execute it with node poc_resources.js
.
Since the choice which UTXO
is taken as input is random, it might take a few tries to trigger the bug!
import { JsonAbi, Script, Provider, WalletUnlocked, Account, Predicate, Wallet, CoinQuantityLike, coinQuantityfy, EstimatedTxParams, BN, Coin, AbstractAddress, Address, Contract, ScriptTransactionRequest } from 'fuels';
const abi: JsonAbi = {
'encoding': '1',
'types': [
{
'typeId': 0,
'type': '()',
'components': [],
'typeParameters': null
}
],
'functions': [
{
'inputs': [],
'name': 'main',
'output': {
'name': '',
'type': 0,
'typeArguments': null
},
'attributes': null
}
],
'loggedTypes': [],
'messagesTypes': [],
'configurables': []
};
const FUEL_NETWORK_URL = 'http://127.0.0.1:4000/v1/graphql';
async function executeTransaction() {
const provider = await Provider.create(FUEL_NETWORK_URL);
const wallet: WalletUnlocked = Wallet.fromPrivateKey('0x37fa81c84ccd547c30c176b118d5cb892bdb113e8e80141f266519422ef9eefd', provider);
const wallet2: WalletUnlocked = Wallet.fromPrivateKey('0xde97d8624a438121b86a1956544bd72ed68cd69f2c99555b08b1e8c51ffd511c', provider);
const sleep = (ms: number) => new Promise((resolve) => setTimeout(resolve, ms));
console.log("Balance wallet before: ", await wallet.getBalance());
console.log("Balance wallet2 before: ", await wallet2.getBalance());
wallet2.transfer(wallet.address, 100);
await sleep(5500);
await wallet.transfer(wallet2.address, 80);
console.log('wallet -> wallet2');
await wallet.transfer(wallet2.address, 80);
console.log('wallet -> wallet2');
console.log("Balance wallet after: ", await wallet.getBalance());
console.log("Balance wallet2 after: ", await wallet2.getBalance());
};
executeTransaction().catch(console.error);
{ "github_reviewed_at": "2024-07-30T21:13:42Z", "github_reviewed": true, "nvd_published_at": "2024-07-30T20:15:04Z", "cwe_ids": [ "CWE-20" ], "severity": "LOW" }