Centrifuge - 0xHelium's results

Lines of code

https://github.com/code-423n4/2023-09-centrifuge/blob/512e7a71ebd9ae76384f837204216f26380c9f91/src/Escrow.sol#L14-L27

Vulnerability details

Impact

The Escrow.sol smart contract receive assets from investors and send back those assets to investors when they withdraw. However some tokens (e.g. USDC, USDT) have a contract level admin controlled address blocklist. If an address is blocked, then transfers to and from that address are forbidden. see here If a user invest in a pool using one of those tokens and after get added to blocklist by these tokens owner, the invested funds get trapped into escrow contract forever.

Proof of Concept

Here is an example of blockable token: https://github.com/d-xo/weird-erc20/blob/04fbd6411f201da59a895dd6d3506913a525dfa9/src/BlockList.sol#L1-L29

// Copyright (C) 2020 d-xo
// SPDX-License-Identifier: AGPL-3.0-only


pragma solidity >=0.6.12;


import {ERC20} from "./ERC20.sol";


contract BlockableToken is ERC20 {
    // --- Access Control ---
    address owner;
    modifier auth() { require(msg.sender == owner, "unauthorised"); _; }


    // --- BlockList ---
    mapping(address => bool) blocked;
    function block(address usr) auth public { blocked[usr] = true; }
    function allow(address usr) auth public { blocked[usr] = false; }


    // --- Init ---
    constructor(uint _totalSupply) ERC20(_totalSupply) public {
        owner = msg.sender;
    }


    // --- Token ---
    function transferFrom(address src, address dst, uint wad) override public returns (bool) {
        require(!blocked[src], "blocked");
        require(!blocked[dst], "blocked");
        return super.transferFrom(src, dst, wad);
    }
}

As we can see if an address is blocked it can never receive or transfer tokens again. This situation result in user funds being trapped everywhere he invested ( in this case Cantrifuge ). However Centrifuge did not implement a withdraw function in the Escrow.sol contract to allow an emergency withdraw of tokens that can potentially be stuck inside forever.

Tools Used

Manual review

Recommended Mitigation Steps

Add an emergency admin withdraw function to withdraw an user funds if he gets blocked by asset contract owner. Here is an example:

function withdraw(address asset, address user) external onlyAdmin {
    IERC20(asset).transfer(msg.sender, balances[user]);
}
modifier onlyAdmin() {
 if(msg.sender != admin) revert();
_;
}

For more transparancy this function should only be called by admin after a governance vote.

Assessed type

ERC20