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Beanstalk

Judging

Beanstalk Part 2

Beanstalk is a permissionless fiat stablecoin protocol built on Ethereum. Its primary objective is to incentivize independent market participants to regularly cross the price of 1 Bean over its dollar peg in a sustainable fashion. This audit is centered around the BIP (Beanstalk Improvement Proposal) that whitelists the BEAN:wstETH Well in the Silo and migrates liquidity underlying Unripe assets from BEAN:ETH to BEAN:wstETH.

Start Date Apr 1st, 2024 (12:00)
End Date Apr 15th, 2024 (12:00)
Time Left 0d/0h/0m
Rewards $35,000 USDC

Beanstalk Codehawks Part 2

Contest Details

Prize Pool

  • Total Pool - 35,000
  • H/M - 30,000
  • Low - 1,500
  • Community Judging - 3,500
  • Starts: Monday, April 01, 2024 Noon UTC
  • Ends: Monday, April 15, 2024 Noon UTC

Stats

  • nSLOC: 1,991
  • Complexity Score: 1203

About

Beanstalk is a permissionless fiat stablecoin protocol built on Ethereum. Its primary objective is to incentivize independent market participants to regularly cross the price of 1 Bean over its dollar peg in a sustainable fashion.

Beanstalk does not have any collateral requirements. Beanstalk uses credit instead of collateral to create Bean price stability relative to its value peg of $1. The practicality of using DeFi is currently limited by the lack of decentralized low-volatility assets with competitive carrying costs. Borrowing rates on USD stablecoins have historically been higher than borrowing rates on USD, even when supply increases rapidly. Non-competitive carrying costs are due to collateral requirements.

In particular, this audit is centered around the BIP (Beanstalk Improvement Proposal) that whitelists the BEAN:wstETH Well in the Silo and migrates liquidity underlying Unripe assets from BEAN:ETH to BEAN:wstETH. You can read more details in the RFC for the update here.

You can read an overview of how Beanstalk works here.

Actors

  • Stalkholder / Silo Member
    • Anyone who Deposits assets on the Deposit Whitelist into the Silo, earning the illiquid Stalk token in doing so. Stalkholders participate in governance and earn Bean seigniorage.
  • gm caller
    • Anyone who calls the gm function to start the next Season.
  • Unripe holder
    • Anyone who holds Unripe Beans or Unripe LP. These assets were distributed to holders of BDV (Bean Denominated Value) at the time of the April 2022 governance exploit. Most Unripe holders have their Unripe assets Deposited in the Silo, and thus are also Stalkholders.
  • Fertilizer holder
    • Anyone who holds Fertilizer, the debt asset earned by participating in Beanstalk's recapitalization.
  • Pod holder
    • Anyone who holds Pods, the Beanstalk-native debt asset. Pods are minting when lending Beans to Beanstalk (Sowing Beans). Not particularly relevant for the scope of this audit.

Scope

Generally, the audit covers the Silo, the Sun and many of their associated libraries. A couple contracts from the Barn (related to Unripe assets) are also in scope.

Specifically, only the following contracts are in scope.

protocol/
└── contracts/
    ├── beanstalk/
    │   ├── AppStorage.sol
    │   ├── barn/
            ├── FertilizerFacet.sol
    │   │   └── UnripeFacet.sol
    │   ├── init/
    │   │   └── InitMigrateUnripeBeanEthToBeanSteth.sol
    │   ├── silo/
    │   │   ├── BDVFacet.sol
    │   │   └── SiloFacet/
    │   │       └── Silo.sol
    │   └── sun/ 
    │       ├── GaugePointFacet.sol
    │       ├── LiquidityWeightFacet.sol
    │       └── SeasonFacet/
    │           └── Oracle.sol
    └── libraries/
        ├── Convert/ 
        │   ├── LibConvert.sol
        │   └── LibUnripeConvert.sol 
        ├── LibBarnRaise.sol
        ├── LibEvaluate.sol
        ├── LibFertilizer.sol
        ├── Minting/ 
        │   └── LibWellMinting.sol
        ├── Oracle/ 
        │   ├── LibChainlinkOracle.sol
        │   ├── LibEthUsdOracle.sol
        │   ├── LibOracleHelpers.sol
        │   ├── LibUniswapOracle.sol
        │   ├── LibUsdOracle.sol
        │   ├── LibWstethEthOracle.sol
        │   └── LibWstethUsdOracle.sol
        ├── Silo/
        │   └── LibWhitelist.sol
        └── Well/
            ├── LibWell.sol
            └── LibWellBdv.sol

Compatibilities

Beanstalk implements the ERC-2535 Diamond standard. It supports various whitelists for Deposits, Minting, Converts, etc., particularly for LP tokens from Basin.

Blockchains:

  • Ethereum

Tokens:

  • ERC-20 (all are accepted in Farm balances, a whitelist is accepted on the Deposit Whitelist, etc.)
  • ERC-1155 (Fertilizer and Deposits are ERC-1155 tokens)

Setup

Clone repo:

git clone https://github.com/Cyfrin/2024-04-beanstalk-2

Install dependencies:

cd Beanstalk/protocol
yarn

Add RPC:

export FORKING_RPC=https://eth-mainnet.g.alchemy.com/v2/{RPC_KEY}

generate:

yarn generate

Test:

yarn test

Known Issues

  • The enrootDeposits functions do not properly emit ERC-1155 events.

    • enrootDeposits updates a user's Unripe Deposits' BDV and issues the corresponding Stalk to the user. The single enrootDeposit function correctly emits the ERC-1155 events, but the multiple variant incorrectly emits a transferSingle event to the 0 address for each Deposit. Given the Beanstalk subgraph does not use these events, and cannot be used to harm the protocol, the fix will be implmented in a separate upgrade to Beanstalk.
  • All findings in the following audit reports