Liquidity Management
Gamma
DeFiFoundry
50,000 USDC
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Submission Details
Severity: medium
Invalid

GmxProxy::createOrder Is Not Compatible With USDT

zebra

Summary

The GmxProxy::createOrder function is incompatible with USDT due to its non-standard “approve-reset” pattern, leading to transaction reverts when USDT is used as a collateral token.

Vulnerability Details

USDT implements a non-standard approve function that requires resetting the approval to 0 before setting a new allowance.

The relevant code from the USDT contract:
https://etherscan.io/address/0xdac17f958d2ee523a2206206994597c13d831ec7

/**
* @dev Approve the passed address to spend the specified amount of tokens on behalf of msg.sender.
* @param _spender The address which will spend the funds.
* @param _value The amount of tokens to be spent.
*/
function approve(address _spender, uint _value) public onlyPayloadSize(2 * 32) {
​
// To change the approve amount you first have to reduce the addresses`
// allowance to zero by calling `approve(_spender, 0)` if it is not
// already 0 to mitigate the race condition described here:
// https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
require(!((_value != 0) && (allowed[msg.sender][_spender] != 0)));
​
allowed[msg.sender][_spender] = _value;
Approval(msg.sender, _spender, _value);
}

According to PerpetualVault.sol,

collateralToken can be ETH, WETH, BTC, LINK, UNI, USDC, USDT, DAI, FRAX.

The GmxProxy::createOrder function does not account for this special requirement, causing transactions to fail when USDT is used as the collateral token.

Additionally, OpenZeppelin’s safeApprove function does not handle this “approve-reset” pattern, making it ineffective for USDT approvals.

Impact

Any attempt to use USDT in GmxProxy::createOrder results in a revert

Tools Used

N/A

Recommendations

Modify the GmxProxy::createOrder to first set approval to 0 before setting the new allowance.

Updates

Lead Judging Commences

n0kto Lead Judge 7 months ago
Submission Judgement Published
Invalidated
Reason: Out of scope
n0kto Lead Judge 7 months ago
Submission Judgement Published
Invalidated
Reason: Out of scope

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