Tadle

Summary

Transfer will always send ETH with a 2300 gas. This can be problematic for interacting smart contracts if gas cost change because their interaction may abruptly break.

Vulnerability Details

The transfer() and send() functions forward a fixed amount of 2300 gas. Historically, it has often been recommended to use these functions for value transfers to guard against reentrancy attacks. However, the gas cost of EVM instructions may change significantly during hard forks which may break already deployed contract systems that make fixed assumptions about gas costs. For example. EIP 1884 broke several existing smart contracts due to a cost increase of the SLOAD instruction.
In the withdraw() function, the protocol uses payable(msg.sender).transfer() to send ETH to msg.sender.

Impact

The use of the deprecated transfer() function for an address will inevitably make the transaction fail when:

The claimer smart contract does not implement a payable function.
The claimer smart contract does implement a payable fallback which uses more than 2300 gas unit.
The claimer smart contract implements a payable fallback function that needs less than 2300 gas units but is called through proxy, raising the call's gas usage above 2300.
Additionally, using higher than 2300 gas might be mandatory for some multisig wallets.

Tools Used

Recommendations

Use call instead of transfer.