feelereth - _getPendingReward() function is vulnerable to manipulation of the rewardPerToken

[sherlock-admin2]

feelereth

high

_getPendingReward() function is vulnerable to manipulation of the rewardPerToken

Summary

_getPendingReward() function is vulnerable to manipulation of the rewardPerToken by a malicious reward contract.

Vulnerability Detail

This assumes enRewardPerToken (the current reward per token from the rewarder contract) will always be >= stRewardPerShare (the stored reward per token).

A malicious rewarder contract could manipulate rewardPerToken() to decrease it below the stored value. This would make share a very large number. When multiplied by the user's balance, it could withdraw unexpectedly large rewards.

Impact

If stRewardPerShare was 100 and the malicious contract returned 50 for rewardPerToken(), share would be 50. This could let the user steal 50x their balance in rewards.

Code Snippet

https://github.com/sherlock-audit/2023-07-blueberry/blob/main/blueberry-core/contracts/wrapper/WConvexPools.sol#L139-L142

Tool used

Manual Review

Recommendation

Store the last enRewardPerToken and compare to make sure it increases each time

[sherlock-admin2]

2 comment(s) were left on this issue during the judging contest.

0xyPhilic commented:

invalid because having a malicious rewarder is purely theoretical so the issue can be considered low

Kral01 commented:

Needs PoC.