Description:
Several functions in the contract allow external calls to transfer tokens and update user data, making the contract potentially vulnerable to reentrancy attacks. Specifically, functions like unstake, unstakeVested, unstakeAll, claimReward, and completeClaimRequest allow users to withdraw or claim tokens without reentrancy protection.

Location:

src/FjordStaking.sol

• unstake function (Line 449)

• unstakeVested function (Line 512)

• unstakeAll function (Line 570)

• claimReward function (Line 616)

• completeClaimRequest function (Line 662)

Issue:
These functions interact with external token contracts (using safeTransfer) before all state changes are finalized. If a reentrant call is made by the token contract or any contract called by the token transfer, it could lead to inconsistent or exploited state changes, such as double withdrawals.

Impact:

• A reentrancy attack could allow a malicious user to repeatedly withdraw funds or claim rewards, potentially draining the contract's balance or receiving more tokens than intended.

Tools used: Manual Review.

Recommendations:
Implement the nonReentrant modifier from OpenZeppelin's ReentrancyGuard or a custom reentrancy guard to protect these functions. Ensure that all state changes are finalized before any external calls.

Potential changes:

• Add the nonReentrant modifier to the unstake, unstakeVested, unstakeAll, claimReward, and completeClaimRequest functions.

Changes needed for which line of code:

• Add nonReentrant Modifier