Bright Emerald Fish - Incorrect index of checkpoint

[sherlock-admin4]

Bright Emerald Fish

Medium

Incorrect index of checkpoint

Summary

If the checkpoint is updated and the previous timestamp and current are the same (i.e they are within the same block) the index returned is incorrect.

Vulnerability Detail

The ProtectedListings::_createCheckpoint function updates the collectionCheckpoints mapping whenever a change in the number of listings occurs and returns the index at which the latest checkpoint is stored.
In the ProtectedListings::_createCheckpoint function if the timestamp of a listing is the same as the previous one in the array the compoundedFactor of the previous checkpoint is changed and used as the updated checkpoint. However, the index is calculated as the length of the array which is incorrect.

Impact

The checkpoint index is incorrect and points to a non-existing array index, and since this is used in calculating the unlock price therefore the unlock price will also be incorrect.

Code Snippet

In https://github.com/sherlock-audit/2024-08-flayer/blob/main/flayer/src/contracts/ProtectedListings.sol#L564-#L567

Tool used

Manual Review

Recommendation