`TwabLib::getTwabBetween` can return innacurate balances if `_startTime` and `_endTime` aren't safely bounded

[code423n4]

Lines of code

https://github.com/GenerationSoftware/pt-v5-prize-pool/blob/4bc8a12b857856828c018510b5500d722b79ca3a/src/PrizePool.sol#L920, https://github.com/GenerationSoftware/pt-v5-twab-controller/blob/0145eeac23301ee5338c659422dd6d69234f5d50/src/libraries/TwabLib.sol#L281, https://github.com/GenerationSoftware/pt-v5-prize-pool/blob/4bc8a12b857856828c018510b5500d722b79ca3a/src/PrizePool.sol#L429

Vulnerability details

M-01 TwabLib::getTwabBetween can return innacurate balances if _startTime and _endTime aren't safely bounded

Vulnerability details

Here's the documentation of the get TwabLib::getTwabBetween function :

File: twab-controller\src\libraries\TwabLib.sol

278:   /**
279:    * @notice Looks up a users TWAB for a time range.
280:    * @dev If the timestamps in the range are not exact matches of observations, the balance is extrapolated using the previous observation.
281:    * @dev Ensure timestamps are safe using isTimeRangeSafe.
282:    * @param _observations The circular buffer of observations
283:    * @param _accountDetails The account details to query with
284:    * @param _startTime The start of the time range
285:    * @param _endTime The end of the time range
286:    * @return twab The TWAB for the time range
287:    */
288:   function getTwabBetween(  //@audit - M01: dev comment (isTimeRangeSafe) doesn't seems to be followed in PrizePool calling it
289:     uint32 PERIOD_OFFSET,
290:     ObservationLib.Observation[MAX_CARDINALITY] storage _observations,
291:     AccountDetails memory _accountDetails,
292:     uint32 _startTime,
293:     uint32 _endTime
294:   ) internal view returns (uint256) {

TwabLib::getTwabBetween function get called in PrizePool::_getVaultUserBalanceAndTotalSupplyTwab, which itself get called by PrizePool::claimPrize returning twab for a specified time-range, which finally is called by PrizePool::isWinner in PrizePool::claimPrize.

The thing is, as well explained by the documentation, values from balance history isn't guaranteed to be accurate the if timestamp at which it is queried time do not fall between :

• (or at) the newest observation in a period
• and the end of that period (period must have ended)

That is because, until a period has ended we cannot be sure the value we are querying haven't changed in the future (from pov of the timestamp)

Impact

This means that if a prize is claimed, but timestamps at which the twab is getting requested do not follow these rules, the Prize Pool contract might distribute prizes based on inaccurate data. This could lead to prizes being distributed to users who should not have won, or not being distributed to users who should have won.

File: prize-pool\src\PrizePool.sol

920:   function _getVaultUserBalanceAndTotalSupplyTwab(
921:     address _vault,
922:     address _user,
923:     uint256 _drawDuration
924:   ) internal view returns (uint256 twab, uint256 twabTotalSupply) {
925:     uint32 _endTimestamp = uint32(_lastClosedDrawStartedAt + drawPeriodSeconds);
926:     uint32 _startTimestamp = uint32(_endTimestamp - _drawDuration * drawPeriodSeconds);
927:     //@audit - dev comment for TwabLib::getTwabBetween doesn't seems to be followed in PrizePool calling it
928:     twab = twabController.getTwabBetween(_vault, _user, _startTimestamp, _endTimestamp);
929: 
930:     twabTotalSupply = twabController.getTotalSupplyTwabBetween(
931:       _vault,
932:       _startTimestamp,
933:       _endTimestamp
934:     );
935:   }

Tools Used

Manual audit

Recommended Mitigation Steps

Add isTimeRangeSafe check (will depend on how devs want to handle it, either a revert or another error management solution) before getTwabBetween to ensure queried balances are acurate, otherwise, prize distibution could be unfair

  function _getVaultUserBalanceAndTotalSupplyTwab(
    address _vault,
    address _user,
    uint256 _drawDuration
  ) internal view returns (uint256 twab, uint256 twabTotalSupply) {
    uint32 _endTimestamp = uint32(_lastClosedDrawStartedAt + drawPeriodSeconds);
    uint32 _startTimestamp = uint32(_endTimestamp - _drawDuration * drawPeriodSeconds);
    //@audit dev comment doesn't seems to be followed in PrizePool calling it
    //@audit added isTimeRangeSafe before getTwabBetween
    require(twabController.isTimeRangeSafe(_vault, _user, _startTimestamp, _endTimestamp), "Time range not safe");
    twab = twabController.getTwabBetween(_vault, _user, _startTimestamp, _endTimestamp);

    twabTotalSupply = twabController.getTotalSupplyTwabBetween(
      _vault,
      _startTimestamp,
      _endTimestamp
    );
  }

Assessed type

Invalid Validation

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Picodes marked the issue as selected for report

[c4-judge]

Picodes marked the issue as primary issue

[c4-judge]

Picodes marked the issue as satisfactory

[asselstine]

Fixed in https://github.com/GenerationSoftware/pt-v5-twab-controller/pull/5