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Forta Staking Vault Audit

OpenZeppelin Security | April 23, 2024

Table of Contents

Summary

Type
DeFi
Timeline
From 2024-02-05
To 2024-02-09
Languages
Solidity
Total Issues
23 (15 resolved, 3 partially resolved)
Critical Severity Issues
1 (1 resolved)
High Severity Issues
1 (1 resolved)
Medium Severity Issues
3 (1 resolved, 1 partially resolved)
Low Severity Issues
9 (8 resolved)
Notes & Additional Information
9 (4 resolved, 2 partially resolved)

Scope

We audited the NethermindEth/forta-staking-vault repository at commit ce87cffbf813e27cc83157933760b51fa44a1885.

In scope were the following files:

 src/
├── FortaStakingVault.sol
├── InactiveSharesDistributor.sol
├── RedemptionReceiver.sol
├── interfaces
│   ├── IFortaStaking.sol
│   └── IRewardsDistributor.sol
└── utils
    ├── FortaStakingUtils.sol
    └── OperatorFeeUtils.sol

System Overview

The Forta Staking Vault project introduces a suite of contracts designed to enhance the user experience of delegating, undelegating, redeeming, and claiming assets in Forta Protocol pools. By utilizing the Forta Staking Vault, users can deposit assets into the system and redeem them later without having to engage directly in the delegation process. The delegation and undelegation processes are managed by a newly introduced role, the operator, who determines to which pools and for how long will assets be staked. The Forta Staking Vault is an extension of the upgradeable version of the ERC-4626 contract from the OpenZeppelin contracts library.

The workflow is as follows:

  • Users deposit FORT tokens into the FortaStakingVault contract and in return receive shares that represent those tokens.
  • The operator delegates some or all of the FORT tokens deposited by users to one or more pools of the FortaStaking contract. When assets are delegated, they are labeled as "active shares" in the FortaStaking contract.
  • The operator can initiate the undelegation process for some or all of the FORT tokens delegated to one or more pools. This action triggers a cooldown period that is recorded in the vault for each pool from which tokens will be undelegated, creates a new InactiveSharesDistributor contract, and sends the corresponding Forta staking shares to initiate the withdrawal and transforms those shares into "inactive shares". Until the cooldown period expires, these assets cannot be withdrawn from the InactiveSharesDistributor contract.
  • Once the cooldown period expires, anyone can trigger the undelegation process for a specific pool that already has an InactiveSharesDistributor contract created, which transfers all the FORT tokens back to the vault for later redemption by users.
  • Users can then redeem and claim their assets. Notably, users can also redeem their assets before the cooldown period has expired. In this case, they will initially redeem a proportion of the assets they hold from the available balance of FORT tokens in the vault and will be able to claim the remaining assets after the cooldown period expires for all the subjects where their assets were being staked. Finally, a fee can be charged when redeeming and claiming assets, which is then sent to a fee treasury set by the admin of the vault.

Aside from the FortaStakingVault contract, two other contracts have an important role in the system:

RedemptionReceiver

Each vault user eventually will have their own RedemptionReceiver contract. This contract is responsible for managing redemptions and claims for the user. It keeps track of all pools with active shares that are ready to be withdrawn from the FortaStaking contract, as well as all distributors holding inactive shares that are either undergoing the cooldown period or are ready for withdrawal.

InactiveSharesDistributor

This ERC-20 contract is responsible for distributing assets to both the vault and the users' RedemptionReceiver contracts. Whenever the operator initiates the undelegation process for a specific FortaStaking pool, a new instance of the InactiveSharesDistributor is deployed. This means that for each pool, there could be one or more InactiveSharesDistributor instances, each potentially holding assets to distribute.

Security Model and Trust Assumptions

Privileged Roles

There are two privileged roles in the system:

  • DEFAULT_ADMIN_ROLE: In charge of setting the redemption fee and the treasury address as well as managing roles defined in the system, using OpenZeppelin's AccessControlUpgradeable contract. Initially set as the deployer of the vault.
  • OPERATOR_ROLE: In charge of delegating and initiating the undelegation process of FORT tokens to different FortaStaking pools. Initially set as the deployer of the vault.

Based on our discussions with Forta contributors, the admin role will be managed by the governance council, and the operator role will be delegated by the governance council.

Critical Severity

Incomplete Implementation of ERC-4626 Base Contract Leading to Asset Management and Usability Issues

The vault contract's adaptation from the ERC-4626 standard demonstrates critical flaws in asset management and functionality due to incomplete overrides of essential functions. Initially, the primary concern centers around the mint function. When users invoke the function, the contract correctly emits shares. However, it fails to update the _totalAssets variable and the pool's asset holdings. This discrepancy leads to a significant issue: the vault's asset tracking becomes inaccurate, which in turn will result in incorrect calculations when users attempt to redeem their shares.

Similarly, the omission of an override for the withdraw function can lead to transactions reverting when users attempt to execute withdrawals. Although this issue has a minor direct impact compared to the asset management flaw, it contributes to a degraded user experience, potentially deterring user interaction with the contract.

Consider modifying the mint and withdraw functions from the ERC-4626Upgradeable contract within the FortaStakingVault contract to accurately reflect withdrawn and minted assets in the _totalAssets variable.

Update: Resolved in pull request #22.

High Severity

Attacker Can Stall Undelegations

The process of undelegating assets from a subject in the FortaStakingVault contract requires two steps:

Firstly, the operator triggers the undelegation process by calling the initiateUndelegate function, which deploys a distributor instance, an ERC-20 token. The vault transfers its FortaStaking shares in the given subject to the distributor, and in return, receives minted distributor tokens that represent its position and are equivalent to the FortaStaking shares transferred to the distributor contract. The distributor also initiates the withdrawal of the assets in the FortaStaking contract and the waiting period is stored in the Vault for that particular subject.

Secondly, once the waiting period passes, users are permitted to call the undelegate function to undelegate all the staked tokens of a specific subject by the vault. However, a problem arises when calculating the amount of FORT tokens to be sent from the distributor back to the vault. Instead of using the amount returned by the withdraw function from the FortaStaking contract, the balance of FORT tokens held by the distributor will be used instead which can be manipulated since anyone can send FORT tokens to the distributor.

If this occurs, the undelegate function will revert when attempting to subtract the assets delegated to the given subject since the amount subtracted will be greater than the one tracked in the _assetsPerSubject variable. This implies that the funds deposited in the distributor will become inaccessible and any subsequent attempts to invoke the undelegate function for that particular subject will fail.

Nonetheless, this is not irreversible as the operator can allocate additional tokens to the subject, thereby increasing the _assetsPerSubject amount to prevent an underflow. However, it may take some time before the operator notices this problem and the attacker could front-run any future delegations to put the undelegation process in a stalled situation again. A step-by-step proof-of-concept for this scenario can be found in this secret gist.

Consider using the amount returned by the withdraw function from the FortaStaking contract instead of the balance of FORT held by the distributor.

Update: Resolved in pull request #24.

Medium Severity

Lack of Event Emissions

The following functions do not emit relevant events after executing sensitive actions or modifying storage variables:

  • The updateFeeBasisPoints function should emit a FeeBasisPointsUpdated event. This event should also be emitted in the initialize function.
  • The updateFeeTreasury function should emit a FeeTreasuryUpdated event. This event should also be emitted in the initialize function.
  • The delegate function should emit a StakeDelegated event.
  • The redeem function should emit a StakeRedeemed event.
  • The deposit function should emit a StakeDeposited event.
  • The claimRedeem function should emit a StakeClaimed event.
  • The undelegate function should emit a StakeUndelegated event.
  • The initiateUndelegate function should emit an UndelegateInitiated event.

Consider emitting events following sensitive changes, including the initial event emission in the constructor where appropriate, and incorporating relevant parameters. This approach will facilitate tracking and alert off-chain clients monitoring the contracts' activity.

Update: Partially resolved in pull request #28. The Nethermind team stated:

Only added the first two suggested and one for redeem. Other functions have plenty of underlying events that can be used for the same, either events of the ERC-4626 or events of FortaStaking, with the exception of redeem which is not calling the ERC-4626 implementation.

Unbounded Loops in Redeem Function May Cause DoS

When multiple delegations exist within the vault, the redeem function's iteration through various subjects and distributors introduces a risk of Denial of Service (DoS) for users. Due to the unbounded nature of these loops, a scenario with numerous delegations and distributors could result in exceeding Polygon's 30 million gas limit upon execution of the redeem function. Although this issue is temporary, it has the potential to significantly degrade user experience.

Consider implementing a limitation on the maximum number of delegations permitted, thereby preventing such undesirable situations.

Update: Acknowledged, not resolved. The Nethermind team stated:

Acknowledged. DoS can only be done by the operator who should know and be cautious about it.

Wrong and Incomplete Docstrings

Throughout the codebase, there are several parts that have wrong or incomplete docstrings:

  • The documentation for the undelegate method within the InactiveSharesDistributor contract inaccurately states that vault shares are transferred to the vault. In reality, these shares are burned and it is the FORT tokens that are sent to the vault instead. In addition, the documentation for the claim function misleadingly indicates its use for claiming a portion of the inactive shares owned by individuals, whereas it actually facilitates the claiming of FORT tokens.

  • The initiateUndelegate, getRedemptionReceiver, and claimRedeem functions in FortaStakingVault.sol do not have their return values documented.

  • The initiateUndelegate and claim functions in InactiveSharesDistributor.sol do not have their return values documented.

  • The claim function in RedemptionReceiver.sol does not have its parameters nor return values documented.

  • The redeem and deposit functions use inheritdoc tags to reference ERC4626Upgradeable docstrings but fail to delineate the modifications from the original implementation.

Consider thoroughly documenting all functions/events (and their parameters or return values) that are part of any contract's public API. When writing docstrings, consider following the Ethereum Natural Specification Format (NatSpec).

Update: Resolved in pull request #26.

Low Severity

Tokens Trapped in the Vault Might Cause Redemptions to Revert in Low FORT Liquidity Scenarios

The redeem function enables users to redeem their staked FORT tokens—or someone else's on their behalf. This function calculates the redeemer's share of the total vault assets and uses this proportion to transfer active staking tokens and distributor shares from the vault to the redemptionReceiver. This allows the user to later claim them through the claimRedeem function when available. Finally, it transfers the corresponding proportion of available FORT tokens in the vault that have not yet been delegated, utilizing the FORT token's balanceOf function for this purpose.

However, during this final operation, if extra tokens are present in the vault—whether they were directly sent to the contract by mistake or otherwise—these tokens will be included in the calculation when deducting the assets transferred to the user from the _totalAssets variable. Notably, the _totalAssets variable does not account for tokens directly transferred to the vault. Consequently, this discrepancy may lead to the redeem function reverting due to an underflow, especially when the last few users attempt to redeem tokens from the vault. A step-by-step proof-of-concept for this scenario can be found in this secret gist.

Consider accounting for all mistakenly sent FORT tokens in the vault in the _totalAssets state variable. Otherwise, consider implementing a sweep function that withdraws the token amount difference between _totalAssets and the actual balance reported by the FORT token contract's balanceOf function.

Update: Resolved in pull request #30.

Not Checking if There Are Assets in the Vault to Redeem

The redeem function in the FortaStakingVault contract allows users to redeem FORT tokens in exchange for shares. This function calculates the proportion of assets to be claimed through the claim function for those assets that are either active or inactive and calculates the same proportion of FORT tokens present in the vault for immediate withdrawal. However, in the case that all the FORT tokens have been delegated and there are no FORT tokens present in the vault, the redeem function will still transfer 0 tokens.

To avoid unnecessary operations and extra gas costs, consider checking whether there are assets in the vault to be transferred to the user in the redeem function.

Update: Resolved in pull request #32.

Lack of Input Validation

Throughout the codebase, there are some instances in which the lack of input validation could lead to different undesired scenarios:

  • The delegate function allows the operator to delegate zero assets to the subject. When a subject has no assets, The subject will be added to the subjects array without the ability to remove it through the undelegate function due to the absence of active shares. Attempting to fix this by delegating assets to the same subject to enable the undelegate functionality would add the subject to the array again.
  • In the initialize function, there are no checks to validate that the feeTreasury is not the address 0 and that the feeInBasisPoints is lower than the FEE_BASIS_POINTS_DENOMINATOR variable, as it happens in the updateFeeTreasury and updateFeeBasisPoints functions respectively, which is inconsistent.

Consider implementing input validations in functions where parameters must be confined within specific boundaries. Furthermore, ensure that variables used across different functions are checked against the same boundaries to maintain consistency and integrity.

Update: Resolved in pull request #34 at commit 959e20a.

Missing Return Values in Functions Impair Protocol Integration and Information Flow

The undelegate function allows anyone to undelegate FORT tokens from the FortaStakingVault contract. However, this function does not return the amount of FORT tokens being withdrawn from the FortaStaking contract (through the undelegate function in the InactiveSharesDistributor contract), making it difficult for users to easily track how many tokens have been withdrawn, either off-chain or within a contract that calls the undelegate function and needs to store it.

A similar situation happens with the delegate function. It allows the operator to stake a given amount of previously deposited FORT tokens for a given subject to the FortaStaking contract through the deposit function. However, although deposit returns how many shares those tokens represent, and delegate has access to it, this value is not returned to the caller.

To avoid hindering off-chain operations and to make the vault more easily integrated with other contracts, consider returning the amount of FORT tokens withdrawn for the former and the amount of shares minted by the FortaStaking contract for the latter.

Update: Resolved in pull request #36.

Redundant State Variable

Throughout the codebase, one variable duplicate another already defined, accessible state variable:

  • The FortaStakingVault contract defines the private _token state variable to track the underlying asset address. However, since this contract inherits from the ERC4626Upgradeable contract, it already has access to this address through the asset function.

Even though introducing this duplicate variable does not pose any security risk, it is unnecessary, error-prone, and can confuse developers and auditors.

To improve clarity and adhere to best practices in smart contract development, consider removing this variable and using the aforementioned getter function instead.

Update: Resolved in pull request #38.

Inadequate Visibility of State Variables in RedemptionReceiver Contract

The visibility of the state variables _subjects and _subjectsPending is set to private, posing a significant usability concern within the Forta Vault's claim functionality. This restricted visibility forces users to depend excessively on the Forta Vault user interface to know the remaining number of FORT tokens available for claim. Users might incorrectly conclude that they have claimed all entitled tokens following the execution of the claimReedem function, unaware that additional subjects may still be pending, awaiting the deadline for eligibility.

The claim function iterates through the _subjects array, verifying the timestamp against _subjectsPending and checking if the subject is in a frozen state. When a subject meets all the criteria, its stake is retrieved, it is then removed from the array, and its related entry in _subjectsPending is eliminated. If a subject fails to meet the necessary conditions, it is either because the user must have invoked the function past a certain deadline or because the subject is currently frozen.

Consider providing public access or creating getter functions. This change would let users independently verify their claimable tokens, reducing dependency on the Forta Vault UI and mitigating the risk of misunderstandings regarding their token claims.

Update: Resolved in pull request #40.

Insufficient Code Coverage

The codebase exhibits insufficient code coverage for branches and functions (currently under 77%). This level of coverage may leave critical portions of the code untested, potentially leading to undetected vulnerabilities.

Consider adding more unit tests to increase the code coverage to above 95%, adhering to best practices for software security and reliability. In addition, integrating code coverage tracking into the repository's Continuous Integration process is advised for ongoing quality assurance.

Update: Acknowledged, will resolve. The Nethermind team stated:

We will improve it after merging all changes associated with other findings, so we can make sure everything is well covered, especially all the branches.

Duplicate Utilization of FortaStakingUtils Library

The project currently replicates the FortaStakingUtils library directly within its codebase instead of leveraging the Forta contracts repository as an external dependency. This approach introduces potential risks of inconsistencies between the version of the FortaStakingUtils used in the project and the latest version available in the Forta contracts repository. Such discrepancies could lead to unforeseen issues and complicate maintenance and updates.

Consider integrating the Forta contracts repository as a dependency. This strategy ensures that the project always utilizes the most current and consistent version of the FortaStakingUtils.

Update: Resolved in pull request #42.

Insufficient Project Information in README.md

The project's README.md file currently lacks substantial content and provides no specific information about the project itself. It appears to be the default file automatically generated by Foundry, which does not offer valuable insights or guidance for users or contributors.

Consider enriching the README.md with detailed project information, including its purpose, features, installation procedures, usage examples, and contribution guidelines. This enhancement will significantly improve the project's documentation, fostering a better understanding of the system and potentially attracting more contributors or users.

Update: Resolved in pull request #57.

Notes & Additional Information

Lack of Security Contact

Providing a specific security contact (such as an email or ENS name) within a smart contract significantly simplifies the process for individuals to communicate if they identify a vulnerability in the code. This practice is quite beneficial as it permits the code owners to dictate the communication channel for vulnerability disclosure, eliminating the risk of miscommunication or failure to report due to a lack of knowledge on how to do so. In addition, if the contract incorporates third-party libraries and a bug surfaces in these, it becomes easier for the maintainers of those libraries to make contact with the appropriate person about the problem and provide mitigation instructions.

Throughout the codebase, there are contracts that do not have a security contact:

Consider adding a NatSpec comment containing a security contact above the contract definitions. Using the @custom:security-contact convention is recommended as it has been adopted by the OpenZeppelin Wizard and the ethereum-lists.

Update: Acknowledged, not resolved. The Nethermind team stated:

No security contact in Forta staking contracts to replicate. Forta users will surely use Forta socials to get in touch.

Inadequate Function Visibility

Throughout the codebase, some functions are defined as public but are not being accessed from the contract where they are defined:

When declaring a function as external, its parameters are not copied to memory; instead, they are accessed directly from calldata. Calldata is a read-only, lower-cost area where function arguments are stored. This means that accessing parameters in external functions can consume less gas than accessing parameters in memory.

Consider changing the visibility of the aforementioned functions to external.

Update: Resolved in pull request #44.

The Implemented Access Control Presents Potential Risks for the Vault

The FortaStakingVault uses the AccessControlUpgradeable to incorporate two rules within the vault: the OPERATOR_ROLE, which will be in charge of everything related to the delegations, and the DEFAULT_ADMIN_ROLE, that is in charge of assigning and revoking the latter role.

As the DEFAULT_ADMIN_ROLE is intended to be assigned to only one address, it is not advisable to use the current AccessControlUpgradeable implementation. Using AccessControlUpgradeable might not effectively prevent mistakes such as assigning the admin role to multiple addresses, granting the role to a wrong address, or revoking its own role.

Consider using the AccessControlDefaultAdminRules contract as an alternative to AccessControlUpgradeable. This allows only one account to possess the DEFAULT_ADMIN_ROLE, ensuring better control. It also establishes a two-step process to shift the DEFAULT_ADMIN_ROLE to a different account and includes a configurable delay between the steps. An additional feature allows for the transfer to be canceled before its acceptance. Furthermore, other roles cannot be utilized to manage the DEFAULT_ADMIN_ROLE.

Update: Partially resolved in pull request #46. The current implementation does not specify an initial delay; it defaults to zero. For enhanced readability and explicitness, we recommend using __AccessControlDefaultAdminRules_init_unchained to set the initialDelay and to grant the DEFAULT_ADMIN_ROLE.

Multiple Instances of Missing Named Parameters in Mappings

Since Solidity 0.8.18, developers can utilize named parameters in mappings. This means mappings can take the form of mapping(KeyType KeyName? => ValueType ValueName?). This updated syntax provides a more transparent representation of a mapping's purpose.

Throughout the codebase, there are multiple mappings without named parameters:

Consider adding named parameters to the mappings to improve the readability and maintainability of the codebase.

Update: Acknowledged, not resolved.

Dependency on Polygon Mainnet Fork for Testing

The project extensively relies on a fork of the Polygon mainnet to validate tests against the current state of contracts intended for integration. While this approach has its merits, the absence of a locally executable testing framework poses significant drawbacks. The dependency on the Polygon mainnet fork requires a constant connection to an RPC endpoint which increases the test execution times and introduces potential points of failure associated with network reliability.

Consider implementing a comprehensive local testing environment. This environment should simulate all external interactions, allowing for both integration tests with the mainnet fork and independent local tests. Adopting this strategy will not only decrease testing durations by eliminating network dependencies but also ensure that testing can proceed uninterrupted by external network issues, thus streamlining the development and debugging processes.

Update: Acknowledged, not resolved.

Usage of msg.sender and _msgSender

Throughout the project, msg.sender is used to identify the sender of transactions. However, all OpenZeppelin contracts, from whom the project's contracts inherit, employ _msgSender instead. If the _msgSender function is overridden in the future, for example, to enable other parties to cover the gas costs of transactions, this adaptation will not be accurately represented in instances where msg.sender is used.

Consider either using _msgSender over msg.sender or documenting this distinction clearly to avoid problems. This will help prevent problems if modifications in how the _msgSender function works are introduced in the future.

Update: Resolved in pull request #48.

Typographical Errors

The following typographical errors were identified in the codebase:

  • FortaStakingVault.sol:

    • Line 19: "stategy" should be "strategy", and "forta" should be capitalized as "Forta"
    • Line 169: "Overrided" should be "Overridden".
    • Line 290: "inmediatly" should be "immediately"
    • Line 291: "crated" should be "created"
    • Line 389: "an user" should be "a user"

  • InactiveSharesDistributor.sol:

    • Line 13: "Inactives shares" should be "Inactive shares"
    • Line 15: "invalidShares" should be "inactive shares"
    • Line 16: "transferrable" should be "transferable"

  • RedemptionReceiver.sol:

    • Line 34: "Initialiazes" should be "Initializes".

Consider resolving these typographical errors, as well as running an automated spelling/grammar checker on the codebase and correcting any identified errors.

Update: Resolved in pull request #50.

Inconsistent Licensing

The project uses multiple licenses, MIT and UNLICENSED, which could cause legal or operational issues.

If this is unintentional, standardizing the license across the codebase is recommended to avoid confusion. If intentional, clearly document the rationale for using multiple licenses and ensure compatibility between them.

Update: Resolved in pull request #52.

Gas and Code Optimizations

Several opportunities for gas and code optimizations have been identified across various functions and contracts, which could significantly improve efficiency and reduce execution costs:

  • For Loop Optimization: Current implementations frequently recalculate array lengths within for loop iterations (e.g., line 86 of the RedemptionReceiver contract and line 315 of the FortaStakingVault contract). Optimizing these loops by caching the array length in a local variable before the loop starts can reduce gas costs and execution times.
  • Redundant Validation Removal: The _validateIsOperator() function appears to be redundant and could be replaced with onlyRole(OPERATOR_ROLE) for role checking, simplifying the codebase and potentially saving gas.
  • Immutable State Variables: Several state variables, such as _token and staking, do not change after contract initialization and thus could be declared as immutable and set in the constructor instead of the initialize function. This change could lower gas costs by reducing storage access.
  • Unnecessary Condition in undelegate: The undelegate function contains a conditional check that is logically unnecessary. If vault shares are greater than zero, it logically follows that vault assets cannot be equal to zero, making the if statement redundant.
  • Local vs. State Variable Usage: Inconsistencies in using local versus state variables have been noted. In this line, use the local variable assetsReceived both times to avoid the unnecessary SLOAD operation.

Update: Partially resolved in pull request #53 and pull request #36. The third item on the list was acknowledged by the Nethermind team

Conclusion

The Forta Staking Vault introduces a way for users who do not want to get involved in all the steps of the delegation of FORT tokens to pools of the Forta protocol to an operator, improving the overall user experience.

One critical-severity and one high-severity issue were identified over the course of the audit: The former arises from not overriding the mint function of the ERC-4626 contract, which would lead to asset management issues, while the latter arises from how assets held by contracts are tracked, which could lead to a temporary DoS of certain functionalities of the vault.

During the fix review, the development team introduced a bug while addressing L01 - Tokens Trapped in the Vault Might Cause Redemptions to Revert in Low FORT Liquidity Scenarios. We believe this issue could have been detected by adhering to more rigorous testing practices. We recommend that the Nethermind team resolve L-07 Insufficient Code Coverage, which they have acknowledged. Additionally, we advise them to consistently verify that all state variables modified in tests align with expected outcomes, including balances.

Several fixes and recommendations were also suggested to improve the readability and clarity of the codebase and facilitate future audits, integrations, and development. Moreover, good documentation practices were also suggested.

 

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