Contest ran 15 June 202218 June 2022

3 day contest

Nested Finance contest

The one-stop Defi app to build, manage and monetize your portfolio.

$35,000 USDC

Total Awards

<div align="center"><img width="400" src="https://user-images.githubusercontent.com/32484870/169264834-35b0831e-c6fd-417e-9675-477424488c60.jpeg"></div> <br/> <div align="center"><a href="https://nested.fi" > https://nested.fi </a></div>

Nested contest details

Scope

TOTAL = 1733 LOC & 18 Contracts

In this README you can find references to smart contracts that are not part of the scope (StakeDAO operator for exemple), these contracts are mentioned because it is important to understand them to have a better view of how the protocol works in general.

Core scope

Contract nameGithub URLLoC
NestedFactoryNestedFactory.sol452
OperatorResolverOperatorResolver.sol59
WithdrawerWithdrawer.sol18
/abstracts/MixinOperatorResolverMixinOperatorResolver.sol68
/abstracts/OwnableProxyDelegationOwnableProxyDelegation.sol35
/libraries/ExchangeHelpersExchangeHelpers.sol21

Operator scope

Contract nameGithub URLLoC
/operators/Beefy/BeefyVaultOperatorBeefyVaultOperator.sol62
/operators/Beefy/BeefyVaultStorageBeefyVaultStorage.sol20
/operators/Beefy/lp/BeefyZapBiswapLPVaultOperatorBeefyZapBiswapLPVaultOperator.sol167
/operators/Beefy/lp/BeefyZapUniswapLPVaultOperatorBeefyZapUniswapLPVaultOperator.sol166
/operators/Paraswap/ParaswapOperatorParaswapOperator.sol35
/operators/Yearn/YearnCurveVaultOperatorYearnCurveVaultOperator.sol176
/operators/Yearn/YearnVaultStorageYearnVaultStorage.sol26
/libraries/CurveHelpersCurveHelpers.sol60
/libraries/StakingLPVaultHelpersStakingLPVaultHelpers.sol92

⚠️ Flat Operator and ZeroEx Operator are out of scope.

Governance scope

Contract nameGithub URLLoC
/governance/OwnerProxyOwnerProxy.sol19
/governance/TimelockControllerEmergencyTimelockControllerEmergency.sol186
/governance/scripts/OperatorScriptsOperatorScripts.sol71

Previous Audits

The preview version has been audited 4 times (from oldest to newest):

⚠️ All issues already surfaced in the previous audit will be "invalid".

New version

This new version includes the corrections of the previous audits and new features.

Fixes from last audit

Ownership architecture (see more)

Pull request: feat: OwnerProxy #116
In order to complete the ownership architecture, we need the OwnerProxy contract in charge of executing scripts for the Timelock (run transactions atomically).

Operators

Beefy Single asset vault

Pull request: [New Operator] - Beefy Single Asset Vault #107.
New operator to deposit/withdraw in Beefy single asset vaults.<br/>
This operator can be deployed on every chains where Beefy is available.

Beefy LP vault

Pull request: [New Operator] - Beefy LP Vault #114.
New operator to deposit/withdraw in Beefy LP asset vaults.<br/>
This operator can be deployed on every chains where Beefy is available.

Paraswap

Pull request: [New Operator] - Paraswap #109.
New operator to swap tokens in Paraswap.<br/>
This operator can be deployed on every chains where Paraswap is available.

Yearn Curve vaults

Pull request: [New Operator] StakeDAO + Yearn (curve pools) #119.
New operator to deposit/withdraw in Yearn vaults that use Curve managed assets.<br/>
This operator can be deployed on every chains where Yearn has Curve vault available.

NOTE: This operator is almost identical to the StakeDAO operator, so we have only included the Yearn operator in the audit scope and not the StakeDAO one.
We factorized the code of these two operators in the libraries StakingLPVaultHelpers.sol and CurveHelpers.sol.

Entry/exit fees management

Pull request: feat: Upgradeable Fees #113.
We had introduced upgradeability of fees and the notion of "EntryFees/ExitFees" (new values) :

  • EntryFees : Applied when funds stay inside of the portfolio.
  • ExitFees : Applied when funds are withdrawed from the portfolio.

Nested asset tokenURI mechanism

Pull request: feat: Update tokenURI mechanism #103
We updated the mechanism to set the tokenURI:

  • Remove mintWithMetadata and backfillTokenURI (with the _tokenURIs map).
  • Add reveal/unrevealed URI
  • Add contract URI

Known issues/topics

Copy my portfolio (fees trick)

A user can copy his own portfolio to reduce the fees. However, a require statement will not fix this issue.

This problem cannot be corrected but only mitigated, since the user can use two different wallets.
Currently the front-end doesn’t allow to duplicate a portfolio with the same address.

Deflationary, Rebase and exotic Tokens

The protocol is not fully compatible with deflationary/rebase tokens. In fact, you can add a deflationary/rebase token to your portfolio but
it can lead to unpredictable behaviors (positive or negative, e.g weird-erc20).
We have chosen to manage the tokens with a fixed amount (the input) after considering several solutions.

There are also tokens that have exotic implementations that will not handle to avoid unpredictable behaviors, or bypass protocol operations.

So, how can we mitigate that ?

We are maintaining a list of all rebase tokens (source coingecko, which is well maintained), but also exotic tokens and prevent users from adding them to their portfolio on the platform.

Low decimals and Fees calculation

We can encounter tokens with different decimals and sometimes 0 decimals. This is the case with MPS. It can be problematic as we can loose precision when calculating fees.

Miscellaneous already surfaced

IssueGithub URLComment
TransferOwnership should be a two step processissues#101
Accidentally calling withdraw twice with the same parameters could withdraw multiple assetsissue#/33It is a front end and not really related to smart contract.
Unbounded number of shareholders can cause DOSissu#s/2

Gas optimizations already surfaced

IssueGithub URLComment
Use of constant keccak variables results in extra hashingissues#71
Use custom errors instead of the revert stringsissues#63
Change the incremental logic from i++ to ++iissues#16
An array’s length should be cached in for-loopsissues#28
Consider introducing an upper limit for _timestamp in updateLockTimestampissues#66We are not sure about an upper limit to set
There is no limit on how many operator that can be addedissues#58
Remove unused ETH variable from FeeSplitterissues#46We don't know if we will remove this variable. It can be very useful to migrate funds (if needed, not used for the moment)
Functions that add or remove operators or shareholders iterate over a whole array, consider using EnumerableSet to store themissues#67
Function withdraw in NestedFactory calls nestedRecords twiceissues#67

Coverage

Run npx hardhat coverage to run test and generate the coverage summary.

When you run npx hardhat coverage, test will be ran with the context you specified in the .env configuration.
Only tests that can be run in the environment you have configured will be run to generate the coverage summary.

To get the total coverage, it is necessary to run npx hardhat coverage with all the existing configurations, to reach all the written tests.

You can find the 3 existing configurations (BSC, ETH and without fork) in .env.example file.

Coverage ran without fork

Global coverage - tested without fork

The missing coverage is tested in the BSC fork context or the ETH fork context

<div align="left"><img style="width:100%; max-width: 1000px" src="https://github.com/code-423n4/2022-06-nested/blob/main/static/coverage-screenshots/without-fork-1.png"></div>

Main contracts - tested without fork

<div align="left"><img style="width:100%; max-width: 1000px" src="https://github.com/code-423n4/2022-06-nested/blob/main/static/coverage-screenshots/without-fork-2.png"></div>

Coverage ran in ETH fork context

Libraries - tested on ETH fork

The rest of the coverage is in the BSC fork coverage context under Libraries - tested on BSC fork.

<div align="left"><img style="width:100%; max-width: 1000px" src="https://github.com/code-423n4/2022-06-nested/blob/main/static/coverage-screenshots/eth-2.png"></div>

CurveHelpers - tested on ETH fork

The rest of the coverage is in the BSC fork coverage context under CurveHelpers - tested on BSC fork.

<div align="left"><img style="width:100%; max-width: 1000px" src="https://github.com/code-423n4/2022-06-nested/blob/main/static/coverage-screenshots/eth-3.png"></div>

Yearn curve vault operator

<div align="left"><img style="width:100%; max-width: 1000px" src="https://github.com/code-423n4/2022-06-nested/blob/main/static/coverage-screenshots/eth-4.png"></div>

Coverage ran in BSC fork context

Libraries - tested on BSC fork

The rest of the coverage is in the ETH fork coverage context under Libraries - tested on ETH fork.

<div align="left"><img style="width:100%; max-width: 1000px" src="https://github.com/code-423n4/2022-06-nested/blob/main/static/coverage-screenshots/bsc-2.png"></div>

CurveHelpers - tested on BSC fork

The rest of the coverage is in the ETH fork coverage context under CurveHelpers - tested on ETH fork.

<div align="left"><img style="width:100%; max-width: 1000px" src="https://github.com/code-423n4/2022-06-nested/blob/main/static/coverage-screenshots/bsc-3.png"></div>

Beefy operators

<div align="left"><img style="width:100%; max-width: 1000px" src="https://github.com/code-423n4/2022-06-nested/blob/main/static/coverage-screenshots/bsc-5.png"></div> <div align="left"><img style="width:100%; max-width: 1000px" src="https://github.com/code-423n4/2022-06-nested/blob/main/static/coverage-screenshots/bsc-6.png"></div>

Links

Contact us 📝

Wardens! If you have any questions, please contact us!

Axxe (Smart contract engineer)

  • Telegram : @axxedev
  • Discord : axxe#8561
  • Schedule a call : Calendly

Adrien (CTO)

  • Telegram : @adrienspt
  • Discord : Adrien | Nested Finance#6564
  • Schedule a call : Calendly

Try the application

If you want to try Nested, go to : https://app.nested.fi/.

It can help to better understand the protocol context.


Introduction

Nested is a decentralized protocol providing customizable financial products in the form of NFTs.
The platform allows users to put several digital assets, i.e. ERC20 tokens, inside an NFT (abbreviated as NestedNFT).
<br/>

Each NestedNFT is backed by underlying assets:

  • Purchased or sold on a decentralized exchange (AMM).
  • Collected/earned after adding liquidity or staking.
  • Exchanged/Minted on a protocol that is not a decentralized exchange.
  • (...)

The main idea is to allow adding modules (operators) to interact with new protocols
and enable new assets, without re-deploying.

The tokens are stored on a self-custodian smart contract.

At the end of the creation process, the user receives the NFT which allows to control all underlying assets of the portfolio.
Furthermore, we allow users to copy other users NestedNFTs. The creator of the initial NestedNFT earns royalties.

Further documentation and details can be found here: https://docs.nested.finance/

Architecture

image

Core contracts

NamePurpose
NestedFactoryEntry point to the protocol. Holds the business logic. Responsible for interactions with operators (submit orders).
NestedAssetCollection of ERC721 tokens. Called NestedNFT across the codebase.
NestedReserveHolds funds for the user. Transferred from the NestedFactory.
NestedRecordsTracks underlying assets of NestedNFTs. (Amount, NestedReserve).
FeeSplitterReceives payments in ERC20 tokens from the factory when fees are sent. Allows each party to claim the amount they are due.
NestedBuyBackerPulls tokens from the FeeSplitter, buys back NST tokens on the market, and burns a part of it.

Upgradability

The contracts NestedAsset, NestedReserve, and NestedRecords are whitelisting multiple factories (to create NFTs, update records, withdraw from reserve,...).

However, we are also using the TransparentUpgradeableProxy for NestedFactory. Then, the users doesn't have to approve multiple times.

We have kept both mechanisms to get the best flexibility.

Lock

The users can lock their NFTs until a certain date (timestamp) by calling updateLockTimestamp. This feature allows the "hold by design".

Operators (modularization)

What is an operator?

NestedFactory is the main smart contract, but it can't work without the Operators.

As mentioned in the introduction, we designed the protocol to be modular.
We want to be able to interact with any protocol in exchange for an ERC20 token.

So, we had to deal with two issues :

  • How to interact with 5, 10, or 20 protocols without blowing up the bytecode size and having too much logic?
  • How to add new interactions without redeploying the NestedFactory contract?

Our solution is called the "Operator"... A new interaction is a new operator and can be added on the fly.
They kind of work like libraries, but since we don't want to redeploy the factory,
they are contracts that are called via delegatecall and referenced by the OperatorResolver.

Operator Resolver

An operator allows performing a precise action, like "swap my token A for a token B" with a specific function, but the operator/interface will change depending on the action/context. To interact with new operators on the fly, we must expose new interfaces to the Factory.
The OperatorResolver will whitelist all the Operator (address) with the selectors (bytes4) since we can't trust the caller to provide these informations.

struct Operator {
    address implementation;
    bytes4 selector;
}

The caller will send the (imported) bytes32 name of the Operator/Function, for example "ZeroEx::performSwap".

The OperatorResolver will return the address + selector if the call is whitelisted and revert if not.

Storage

Since the operators are called via delegatecall: how can we store/retrieve useful data?
<br>In fact, we cannot trust the Factory to provide all the data, like the address of the protocol. It must be stored and managed by the owner.

When deploying an operator, it will also deploy the storage contract and transfer the ownership to msgSender().

Diagram

image

Contracts

NamePurpose
OperatorResolverAllows the factory to identify which operator to interact with.
MixinOperatorResolverAbstract contract to load authorized operators in cache.
ZeroExOperatorPerforms token swaps through 0x (read more).
ZeroExStorageZeroExOperator storage contract. Must store the 0x swapTarget.
FlatOperatorHandles deposits and withdraws. No interaction with any third parties (read more).
BeefyVaultOperatorHandles deposits and withdraws in a Beefy single vault (native or non-native).
BeefyZapBiswapLPVaultOperatorHandles deposits and withdraws in a Beefy Biswap LP vault using zapper.
BeefyZapUniswapLPVaultOperatorHandles deposits and withdraws in a Beefy UniswapV2 LP vault using zapper.
BeefyVaultStorageHandles whitelisting of Beefy Vault or Zapper.
ParaswapOperatorPerforms token swaps through Paraswap.

More operators will be added. e.g. CurveOperator or SynthetixOperator

Orders

The NestedFactory is using the operators to interact with other protocols. The call from the Factory to an Operator is an "Order".

An Order has several information:

  • The operator/selector to use
  • The token processed (swapped, stacked,...) by the operator (from the portfolio or wallet).
  • The calldatas (without the selector).
struct Order {
    bytes32 operator;
    address token;
    bytes callData;
}

It helps us to make one interaction, but we want to make multiple interactions. For example, to create a portfolio with multiple tokens, we need to "batch" these orders.

There are two types of "Batched Orders" processed by the Factory to create or edit Portfolios :

Batched Input Orders

<div align="center"><img src="https://github.com/code-423n4/2022-06-nested/blob/main/static/input-orders.png" width="650"></div>
  • One same input for every orders but multiple outputs.
  • 0.3% fee on the input.
  • The input (source) is from a wallet or a porfolio owned by the transactions signer.
  • The ouput (destination) is the portfolio owned by the transactions signer (only).
struct BatchedInputOrders {
    IERC20 inputToken;
    uint256 amount;
    Order[] orders;
    bool fromReserve;
}

Batched Output Orders

<div align="center"><img src="https://github.com/code-423n4/2022-06-nested/blob/main/static/output-orders.png" width="650"></div>
  • Multiple inputs for every orders but one output.
  • 0.3% fee on the output if operation does not reduce TVL, 0.8% if it does.
  • The input (source) is the portfolio owned by the transactions signer (only).
  • The ouput (destination) is from a wallet or a portfolio owned by the transactions signer.
struct BatchedOutputOrders {
    IERC20 outputToken;
    uint256[] amounts;
    Order[] orders;
    bool toReserve;
}

Example processInputOrders flow

<div align="center"><img src="https://github.com/code-423n4/2022-06-nested/blob/main/static/processInputOrders.png" width="1200"></div>

Nested Factory interaction with the Nested Reserve and Nested Records

The Nested Reserve stores underlying assets of all NestedNFTs. The Nested Records keeps track of which underlying assets are associated with a specific NestedNFT.
Hence, each time the Nested Factory needs to interact with user funds (which are represented as a NestedNFT), it will first check the balance of tokens associated with the NestedNFT through Nested Records. If needed, it will then transfert funds to the Nested Reserve or withdraw funds from it.

Native Token Management

The Nested protocol only handles ERC20 when calling operators.
If the msg.sender is not the withdrawer, the sent ETH used to feed a portfolio are automatically converted to WETH when received.

WETH Conversion

The conversion from ETH to WETH is done when submitting an order through _submitInOrders or _submitOutOrders.

Before submitting orders, the NestedFactory transfers the input tokens from the NestedReserve (or the msg.sender) to the factory and converts the sent ETH to WETH.

Use of ETH in operators

There are some operators who use ETH directly and not WETH.
In this case, the operator uses the Withdrawer to get the ETH back from the WETH contract before using it.

Only the Withdrawer can send ETH to the NestedFactory without automatic WETH conversion.

Royalties

Royalties are a part of the fee collected by the protocol and they are collected during every step of a copied portfolio lifecycle (copy, update, deposit, withdraw).

Fees distribution

For now, the fees are shared equally between portfolio creators (as royalties) and Nested.

First scenario: When a portfolio is created from scratch, all fees go to Nested Finance Ltd and there are no royalties.<br/>
Second scenario: When a portfolio is replicated, the fees are shared equally between Nested Finance Ltd. and the original creator of the Nested portfolio.

This distribution is done in the feeSplitter.sol with the ratio between the royaltiesWeight and the shareholders weights.
Currently, we have royaltiesWeight = 50 and one shareholder (Nested) with weight = 50.

totalWeights always equals royaltiesWeight + all shareholders weights

Ownership & Governance

Some functions of the protocol require admin rights (onlyOwner using Ownable from OpenZeppelin). Same with the TransparentUpgradeableProxy which need an Admin.

<img width="1011" alt="image" src="https://github.com/code-423n4/2022-06-nested/blob/main/static/ownership.png">

The contracts are owned by the OwnerProxy which is a DSProxy fork without a cache, where only the Timelock can execute the scripts.

The TimelockControllerEmergency is a TimelockController fork.
It introduces the "Emergency Role" to execute a transaction in an instantaneous way.
Only the "Emergency Multisig" has this role, with 5 members and 5 approvals needed (in the case of an urgent fix).
On the other hand, the "Operational Multisig" can schedule/execute transactions with a 6-hours delay, with 3 members and 2 approvals needed.

Development & Testing

Setup

  • Install Node > 12
  • Install Yarn
  • Run yarn install
  • Run cp .env.example .env
  • Insert a dummy mnemonic and a mainnet api key in the .env file

Run tests

Tests can be run without fork, with a BSC fork or with an ETH fork by running yarn test.
You can configure how to run the tests by configuring your .env file as follow:

  • To run the tests without fork:
FORKING="false"
  • To run the tests with BSC fork:
FORKING="true"
FORK_CHAINID="56"
FORK_URL="https://bsc-dataseed.binance.org/"
  • To run the tests with BSC fork:
FORKING="true"
FORK_CHAINID="1"
FORK_URL="<YOUR_ETH_RPC_ENDPOINT_URL>"

Commands

  • Start a local blockchain
    yarn run

  • Start a hardhat console
    yarn console

  • Compile
    yarn compile

  • Generate typechain files
    yarn typechain

  • Run tests
    yarn test

License

GNU General Public License v3