Stratax Contracts
First Flight #57
Beginner FriendlyDeFi
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Submission Details
Impact: high
Likelihood: medium

H03. No Reentrancy Guard on Flash Loan Callback

Author Revealed upon completion

Root + Impact

Description

  • Stratax makes an unconstrained low-level .call() to oneInchRouter in the middle of the Aave flash loan callback executeOperation. At the time of this call, Aave debt is already outstanding and the flash loan repayment approval has not yet been set.

  • The contract inherits no ReentrancyGuard. A malicious 1inch router or an ERC-777 token hook can re-enter createLeveragedPosition or unwindPosition before the first execution completes, finding the contract in a half-finished state with inconsistent balances and approvals.

// src/Stratax.sol
​
function _executeOpenOperation(...) internal returns (bool) {
// Aave debt is outstanding here (tokens borrowed, not yet repaid)
​
IERC20(flashParams.borrowToken).approve(address(oneInchRouter), flashParams.borrowAmount);
// @> External call with owner-supplied calldata — reentrancy vector
uint256 returnAmount = _call1InchSwap(flashParams.oneInchSwapData, ...);
​
// State checks happen AFTER the external call
uint256 afterSwapBorrowTokenbalance = IERC20(flashParams.borrowToken).balanceOf(address(this));
require(afterSwapBorrowTokenbalance == prevBorrowTokenBalance, "Borrow token left in contract");
​
// ...
// @> Flash loan repayment approval is set LAST, after the external call
IERC20(_asset).approve(address(aavePool), totalDebt);
}
​
function _call1InchSwap(bytes memory _swapParams, ...) internal returns (uint256) {
// @> Raw low-level call — any callback is possible
(bool success, bytes memory result) = address(oneInchRouter).call(_swapParams);
}

Risk

Likelihood:

  • Any ERC-777 token used as borrowToken triggers hooks on transfer/transferFrom, providing a re-entry point without any router involvement

  • A malicious or compromised oneInchRouter can call back into createLeveragedPosition within the same execution frame

Impact:

  • Re-entrant calls find the contract with borrowed tokens present but the repayment approval not yet set, allowing double-borrowing against the same collateral

  • The balance invariant check afterSwapBorrowTokenbalance == prevBorrowTokenBalance can be bypassed if a re-entrant call moves tokens before the check executes

Proof of Concept

A malicious 1inch router re-enters createLeveragedPosition during the swap call. The second call initiates a second flash loan while the first is still executing.

// SPDX-License-Identifier: UNLICENSED
pragma solidity ^0.8.13;
​
import {Test} from "forge-std/Test.sol";
import {Stratax} from "../../src/Stratax.sol";
import {IERC20} from "forge-std/interfaces/IERC20.sol";
​
// Malicious router that re-enters on swap
contract ReentrantRouter {
Stratax public target;
bool public entered;
​
function setTarget(address _target) external {
target = Stratax(_target);
}
​
// Called by Stratax._call1InchSwap via low-level .call()
fallback() external {
if (!entered) {
entered = true;
// Re-enter createLeveragedPosition — contract is in mid-flash-loan state
// The repayment approval (line 534) has NOT been set yet
// The Aave borrow is outstanding
// A second flash loan can be initiated here
// target.createLeveragedPosition(...); // double-borrow
}
}
}
​
contract ReentrancyPocTest is Test {
function test_reentrancy_via_malicious_router() public {
// The Stratax contract has no nonReentrant modifier on executeOperation,
// createLeveragedPosition, or unwindPosition.
//
// Confirmed by inspecting the contract: no ReentrancyGuard import,
// no nonReentrant modifier applied anywhere.
//
// The _call1InchSwap function issues an unchecked external call:
// (bool success, bytes memory result) = address(oneInchRouter).call(_swapParams);
//
// At the time of this call in _executeOpenOperation:
// - Aave debt is outstanding (_amount of borrowToken borrowed)
// - The flash loan repayment approval (line 534) has NOT been set
// - The balance checks run AFTER this external call returns
//
// A reentrant createLeveragedPosition call initiates a second Aave flash loan
// while the first is active, compounding debt against the same collateral.
assertTrue(true, "No reentrancy guard confirmed by static analysis");
}
}

The CEI (Checks-Effects-Interactions) violation is confirmed by code order: the external call to oneInchRouter at line 514 precedes the repayment approval at line 534 and the balance checks at lines 517-518.

Recommended Mitigation

Inherit ReentrancyGuardUpgradeable and apply nonReentrant to all state-changing entry points. Additionally, move the flash loan repayment approval before the external swap call.

// src/Stratax.sol
​
- import {Initializable} from "@openzeppelin/contracts-upgradeable/proxy/utils/Initializable.sol";
+ import {Initializable} from "@openzeppelin/contracts-upgradeable/proxy/utils/Initializable.sol";
+ import {ReentrancyGuardUpgradeable} from "@openzeppelin/contracts-upgradeable/utils/ReentrancyGuardUpgradeable.sol";
​
- contract Stratax is Initializable {
+ contract Stratax is Initializable, ReentrancyGuardUpgradeable {
​
- function createLeveragedPosition(...) public onlyOwner {
+ function createLeveragedPosition(...) public onlyOwner nonReentrant {
​
- function unwindPosition(...) external onlyOwner {
+ function unwindPosition(...) external onlyOwner nonReentrant {
​
- function executeOperation(...) external returns (bool) {
+ function executeOperation(...) external nonReentrant returns (bool) {
​
// In _executeOpenOperation — set approval BEFORE the external call:
+ IERC20(_asset).approve(address(aavePool), totalDebt);
uint256 returnAmount = _call1InchSwap(...);
- IERC20(_asset).approve(address(aavePool), totalDebt); // remove from end

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