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26259 - [SC - Insight] txHash collision is possible.md

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txHash collision is possible

Submitted on Nov 29th 2023 at 18:23:56 UTC by @Madalad for Boost | DeGate

Report ID: #26259

Report type: Smart Contract

Report severity: Insight

Target: https://etherscan.io/address/0xf2991507952d9594e71a44a54fb19f3109d213a5#code

Impacts:

  • Contract fails to deliver promised returns, but doesn't lose value

Description

Bug Description

If the admin wishes to make the same call more than once with the same eta, this is impossible due to the fact they would share the same txHash. The admin would have to queue the transaction, wait at least 45 days, execute it, then queue it again and wait a further 45 days.

Impact

Queueing two similar transactions causes the first to be overwritten, potentially deceiving the admin and/or users.

Risk Breakdown

Difficulty to Exploit: Easy Weakness: CVSS2 Score:

Recommendation

While it is possible to workaround this issue fairly simply, e.g. altering the eta to differ by one second, implementing some form of nonce in the hash calculation is conventional and provides the least amount of confusion/inconvenience.

References

Proof of concept

See below the proof of concept in the form of a foundry test file.

// SPDX-License-Identifier: UNLICENSED
pragma solidity ^0.8.0;

pragma experimental ABIEncoderV2;

import "forge-std/Test.sol";
import "../../../src/contracts/timelock/Timelock.sol";

contract CollisionTest is Test {
    Timelock public timelock;

    address public admin = makeAddr("admin");
    uint256 public delay = 45 days;

    function setUp() public {
        vm.startPrank(admin);
        timelock = new Timelock({
            admin_: admin,
            delay_: delay
        });
        vm.stopPrank();
    }

    function testCollision() public {
        // Make transaction
        address target = makeAddr("target");
        uint256 value = 0;
        string memory signature = "";
        bytes memory data = abi.encode("data");
        uint256 eta = block.timestamp + delay;

        // Queue transaction twice
        vm.startPrank(admin);
        timelock.queueTransaction(target, value, signature, data, eta);
        timelock.queueTransaction(target, value, signature, data, eta);

        // Execute first transaction
        vm.warp(block.timestamp + delay);
        timelock.executeTransaction(target, value, signature, data, eta);

        // Cannot execute second transaction
        vm.warp(block.timestamp + delay);
        vm.expectRevert("Timelock::executeTransaction: Transaction hasn't been queued.");
        timelock.executeTransaction(target, value, signature, data, eta);
    }
}

Output:

Running 1 test for test/timelock/PoCs/Collision.t.sol:CollisionTest
[PASS] testCollision() (gas: 57777)
Test result: ok. 1 passed; 0 failed; 0 skipped; finished in 109.99ms
Ran 1 test suites: 1 tests passed, 0 failed, 0 skipped (1 total tests)