A malicious early user/attacker can manipulate the apxGMX/apxGLP 's pricePerShare to take an unfair share of future users' deposit

[code423n4]

Lines of code

https://github.com/code-423n4/2022-11-redactedcartel/blob/03b71a8d395c02324cb9fdaf92401357da5b19d1/src/vaults/AutoPxGmx.sol#L370-L403

Vulnerability details

Impact

A well known attack vector for almost all shares based liquidity pool contracts, where an early user can manipulate the price per share and profit from late users' deposits because of the precision loss caused by the rather large value of price per share.

A malicious early user can deposit() with 1 wei of pxGMX as the first depositor of the apxGMX, and get 1 wei of shares.

Then the attacker can send 10000e18 - 1 of pxGMX and inflate the price per share from 1.0000 to an extreme value of 1.0000e22 ( from (1 + 10000e18 - 1) / 1) .

As a result, the future user who deposits 19999e18 will only receive 1 wei (from 19999e18 * 1 / 10000e18) of shares token.

They will immediately lose 9999e18 or half of their deposits if they redeem() right after the deposit().

Proof of Concept

https://github.com/code-423n4/2022-11-redactedcartel/blob/03b71a8d395c02324cb9fdaf92401357da5b19d1/src/vaults/PirexERC4626.sol#L60-L78
https://github.com/code-423n4/2022-11-redactedcartel/blob/03b71a8d395c02324cb9fdaf92401357da5b19d1/src/vaults/AutoPxGmx.sol#L164-L166
https://github.com/code-423n4/2022-11-redactedcartel/blob/03b71a8d395c02324cb9fdaf92401357da5b19d1/src/vaults/AutoPxGmx.sol#L339-L362
https://github.com/code-423n4/2022-11-redactedcartel/blob/03b71a8d395c02324cb9fdaf92401357da5b19d1/src/vaults/PirexERC4626.sol#L167-L176

Tools Used

None

Recommended Mitigation Steps

Consider requiring a minimal amount of share tokens to be minted for the first minter, and send a part of the initial mints as a reserve to the DAO so that the pricePerShare can be more resistant to manipulation.

[c4-judge]

Picodes marked the issue as duplicate of #407

[c4-judge]

Picodes marked the issue as satisfactory

[c4-judge]

Picodes changed the severity to 3 (High Risk)

[C4-Staff]

JeeberC4 marked the issue as duplicate of #275