Fjord Token Staking

Summary

A medium severity vulnerability has been identified in the unstake function of the FjordStaking contract. The current implementation lacks proper input validation for the _epoch parameter, which could lead to an arithmetic underflow when calculating the difference between the current epoch and the input epoch. This could result in unexpected behavior, including bypassing the intended lock period for unstaking.

Vulnerability Details

The vulnerability is present in the unstake function:

The issue lies in the calculation currentEpoch - _epoch. If _epoch is greater than currentEpoch, this subtraction will result in an arithmetic underflow, as these variables are of type uint16. In Solidity 0.8.x, which this contract uses, arithmetic underflows cause the transaction to revert.

Impact

The impact of this vulnerability includes:

1. Unexpected Reverts: Transactions may revert due to arithmetic underflow rather than the intended UnstakeEarly error, leading to confusion for users and developers.

Tools Used

Manual

Recommendations

To address this vulnerability and improve the robustness of the unstake function, we recommend adding an explicit check to ensure that the input _epoch is not greater than the currentEpoch. Here's the suggested fix:

This modification ensures that:

1. The function reverts with a clear error message if a future epoch is provided.

2. It prevents any potential arithmetic underflow in the subsequent calculations.