Users can be forced to claim assets at bad rate in some cases

Summary

In balanced vault contract, anyone can call claim assets for other accounts; malicious users could abuse this function to force other users to receive less assets than they expect.

Vulnerability Detail

When claiming asset, pro rate, in which users will receive less assets than expect, will be applied when total collateral is less than total unclaimed amount. So after redeeming shares and converting it to assets, users might not want to claim assets right away in this scenario, for they will receive less token amount. However, other users can force them to claim via claim() function because there is no restrict on this function to claim for other accounts.

Impact

Users will be forced to receive less assets in some scenarios.

Code Snippet

https://github.com/sherlock-audit/2023-05-perennial/blob/main/perennial-mono/packages/perennial-vaults/contracts/balanced/BalancedVault.sol#L211-L228

Tool used

Manual Review

Recommendation

Only account owner (msg.sender == account) can claim asset for their account.

KenzoAgada commented 1 year ago

While the general claim pro-rata mechanism has already been reported in the Veriside audit (issue 002) and acknowledged by the protocol, this submission correctly adds that a user can pro-rata claim other user's assets, even if they preferred to avoid realizing losses and stay in the vault until collateral recovers. This will make users lose funds, and increase the malicious user's own amount of rewards, for when the collateral recovers.

arjun-io commented 1 year ago

This is a great find. We will think about whether or not we want to fix this as the unpermissioned claim is currently used by the protocol for better UX with the MultiInvoker