Core Contracts

Summary

VeRaac creates checkpoints each time a user calls lock, increase or extend. Only the timestamp and bias is stored. Since the slope is missing from these checkpoints, protocol is unable to retrieve the votingPower for a given timestamp from them.

Vulnerability Details

Each time lock/increase/extend is called, calculateAndUpdatePower is resposible to save the latest timestamp, bias, and slope in _votingState.points[user] variable.

The bias and slope can be defined as:

• Bias: The initial voting power at the time of locking.

• Slope: The rate at which voting power decreases per second.

  The voting power for a voting-escrow system decreases linearly and can be defined by :

  votingPower = bias − slope × timePassed

The lock/ increase/ extend functions are also creating a checkpoint, saving only the bias and the corresponding timestamp for the user.

To know the true voting power an user has you need all 3. Protocol is unable to compute the voting power at a given time using the checkpoints.
The checkpoints works as a snapshot, allowing protocol to interogate a user's votingPower at any given time.

For example this is needed when users must vote for a governance proposal. Users must vote with their voting power at a given time (eg. proposal time creation) to ensure fairness and that proposal results can't be manipulated.

Note: there is another issue reported in a separate submission related to the fact protocol doesn't read votingPower from the snapshots.

Impact

The voting power at a given timestamp can't be used.

The governance and gauge rewards allocation are susceptible to manipulations.

Tools Used

Recommendations

When a checkpoint is created save the slope too beside bias and timestamp.

Ensure that getPastVotes function calculates correctly the voting power using the formulla :
votingPower = bias − slope × timePassed.