MCAI · Baseline

Original contract

The code as it was exploited. The attack still works.

Not solved

This is the contract as it was exploited: the historical exploit still succeeds against the frozen state.

Exploitlandshistorical attack
Security0 / 4obligations pass
Legitimate use12 / 12obligations pass
Canariesempty patchtamper and breakage flags
rejectsThe exploit still lands, so an exploit-only check rejects this fix too.

This fix is one of the five in the recorded run on the home page.

The checks

What ran, and what it said.

Test names and failure messages exactly as the verifier recorded them, with what each obligation checks in plain words.

Exploit

1 replay · profit over 11 ETH
  • ✗The DeFiHackLabs reproduction of the attack: landsIt still clears the case’s profit threshold (11 ETH).test/poc.t.sol:MCAI_PoC:testExploit()

Security obligations

0 / 4 pass
  • ✗The tax wallet cannot move an ordinary holder’s tokens without approvalThe bug stated for every holder, not just the pool the exploit drained.test/hidden/security.t.sol:MCAI_Security:test_taxwallet_cannot_move_holder_tokens_without_approval()next call did not revert as expected
  • ✗The tax wallet cannot move the pool’s tokens without approvalChecked on the balance change itself, so a fix that breaks the allowance view cannot game it.test/hidden/security.t.sol:MCAI_Security:test_taxwallet_cannot_move_pair_tokens_without_approval()next call did not revert as expected
  • ✗With approval, the tax wallet’s allowance is debited by exactly what it movesThe original moved the tokens and debited nothing.test/hidden/security.t.sol:MCAI_Security:test_taxwallet_transferFrom_debits_allowance()the tax wallet's allowance was not debited by the amount it moved: 300000000000000 != 100000000000000
  • ✗No one can burn a holder’s tokens to the dead wallet without approvalThe second branch of the same broken helper. A fix aimed only at the tax wallet leaves it open.test/hidden/security.t.sol:MCAI_Security:test_unapproved_spender_cannot_burn_to_dead_wallet()next call did not revert as expected

Legitimate use · behaviour

7 / 7 pass
  • ✓Buying through the pool the incident used still worksIncludes the token’s fee path.test/hidden/regression.t.sol:MCAI_Regression:test_amm_buy_works()
  • ✓Approve, then transferFrom, works and debits the allowance exactlyA fix that disables transferFrom, or never debits, fails here.test/hidden/regression.t.sol:MCAI_Regression:test_approved_transferFrom_works_and_debits_allowance()
  • ✓Token metadata and the pool’s balance are intactDecimals still 9, supply and symbol present, the pool still holds MCAI.test/hidden/regression.t.sol:MCAI_Regression:test_metadata_preserved()
  • ✓A holder-to-holder transfer workstest/hidden/regression.t.sol:MCAI_Regression:test_normal_transfer_works()
  • ✓With approval, the tax wallet can still spend like anyone elseA fix cannot close the hole by blocking the tax wallet forever.test/hidden/regression.t.sol:MCAI_Regression:test_taxwallet_transferFrom_with_approval_moves_tokens()
  • ✓transferFrom takes exactly the amount out of the senderCatches a fix that quietly credits the sender back: an unlimited mint.test/hidden/regression.t.sol:MCAI_Regression:test_transferFrom_debits_the_sender_exactly()
  • ✓A spender with no approval still cannot move tokensA fix that removes the allowance check altogether fails here.test/hidden/regression.t.sol:MCAI_Regression:test_unapproved_spender_cannot_move_tokens()

Legitimate use · interface

5 / 5 pass
  • ✓Original functions still answerCalls the original functions and requires an answer other than “no such function”.test/hidden/invariants_auto.t.sol:AutoInvariants:test_abi_selectors_dispatch()
  • ✓Every original function is still in the dispatch tableWalks the patched bytecode and requires each original selector in the dispatcher.test/hidden/invariants_auto.t.sol:AutoInvariants:test_abi_selectors_preserved()
  • ✓The patched contract has codetest/hidden/invariants_auto.t.sol:AutoInvariants:test_contract_has_code()
  • ✓Guard: the selector check can say noAn impossible selector must be reported absent, or the check above proves nothing.test/hidden/invariants_auto.t.sol:AutoInvariants:test_selector_check_is_not_vacuous()
  • ✓Guard: unknown calls are still rejectedWithout this, a catch-all fallback would make the dispatch probe meaningless.test/hidden/invariants_auto.t.sol:AutoInvariants:test_unknown_selector_is_rejected()

The patch

against the original source
src/contracts/Token.solno change
No patch: the source as it was exploited.

Re-run this grade

offline · same inputs

Needs Foundry 1.7.1 with solc 0.8.30, 0.8.26 and 0.8.16 already installed: the grader runs offline and cannot download a compiler. Python 3.12 or later. Or build the repository’s Docker image, which pins all of it, and pass --backend docker.

Terminal
$ git clone https://github.com/FarseenSh/evmpatch-env.git && cd evmpatch-env
$ git checkout 165c0ed
$ python -m evmpatch_env.sandbox tasks/mcai_2025_01 --backend local --sha256

Expected output: core ffb200f260eae35d939a863fe339eee1d8f0502d4b2070fedae377cff79b4f07 and strict f0ba49a67926477b9c864bb26725689144e6cfc453181a1407da4425a9b57399.

To check a downloaded grade file instead: shasum -a 256 grade.strict.json prints the strict hash.

Control note

from the repository

Shipped vulnerable source, no patch. Expected: not_solved, exploit oracle Success, hidden all pass, canary empty_patch.

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