NGP · Non-repair

Cosmetic change

A rename with no effect on behaviour. The exploit still lands.

Not solved

The historical exploit still succeeds against the frozen state.

Exploitlandshistorical attack
Security0 / 4obligations pass
Legitimate use10 / 10obligations pass
Canariesnonetamper and breakage flags
rejectsThe exploit still lands, so an exploit-only check rejects this fix too.
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 100,000 USDT
  • ✗The DeFiHackLabs reproduction of the attack: landsIt still clears the case’s profit threshold (100,000 USDT).test/poc.t.sol:NGP_PoC:testExploit()

Security obligations

0 / 4 pass
  • ✗A direct transfer to the pool moves nothing out of itCatches a fix that special-cases the router and leaves the same branch open.test/hidden/security.t.sol:NGP_Security:test_direct_transfer_to_the_pair_moves_nothing_out_of_it()a direct transfer to the pair moved NGP OUT of it: the pool is still being drained inside someone else's transfer: 3500000000000000000000 != 0
  • ✗An ordinary sell moves no tokens out of the poolThe original moved 70% of every sell out of the pair.test/hidden/security.t.sol:NGP_Security:test_ordinary_sell_moves_no_tokens_out_of_the_pair()a sell moved NGP OUT of the pair: the seller is draining the pool inside their own transfer (amm-reserve-manipulation): 3630547125325919886628 != 0
  • ✗The pool keeps every token a sell sends itAsserted on balances, so a fix that only hides the transfer events is still caught.test/hidden/security.t.sol:NGP_Security:test_pair_keeps_every_token_an_ordinary_sell_sends_it()the pair did not keep everything the sell sent it: tokens leaked out of the pool during the seller's transfer: 2593247946661371347594 != 6223795071987291234222
  • ✗Treasury and reward fees are not paid out of the poolFees must be funded by the party making the trade.test/hidden/security.t.sol:NGP_Security:test_treasury_and_reward_are_not_funded_out_of_the_pair()the treasury fee on a sell was taken out of the pair, not out of the seller: 2593247946661371347592 != 0

Legitimate use · behaviour

5 / 5 pass
  • ✓A buy-then-sell round trip through the pool worksThe sell leg is where the bug lived, so deleting selling fails here.test/hidden/amm_regression.t.sol:NGP_AmmRegression:test_amm_buy_then_sell_round_trip()
  • ✓Trading stays switched onChecks the buy and sell switches in storage. Turning either off is not a fix.test/hidden/amm_regression.t.sol:NGP_AmmRegression:test_trading_flags_still_open()
  • ✓Token metadata and the pool’s balance are intactDecimals still 18, supply present, the pool still holds NGP.test/hidden/regression.t.sol:NGP_Regression:test_metadata_preserved()
  • ✓A wallet-to-wallet transfer workstest/hidden/regression.t.sol:NGP_Regression:test_normal_transfer_works()
  • ✓The price view still workstest/hidden/regression.t.sol:NGP_Regression:test_price_view_works()

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.sol+2 −2
@@ -291,8 +291,8 @@291291            uint256 treasuryAmount = (value * treasuryRate) / RATIO_PRECISION;292292            uint256 rewardAmount = (value * rewardRate) / RATIO_PRECISION;293293            uint256 burnPoolAmount = treasuryAmount + rewardAmount;294−            uint poolAmount = this.balanceOf(mainPair);295−            if (poolAmount > burnPoolAmount) {294+            uint pairTokenBalance = this.balanceOf(mainPair);   // renamed, nothing else295+            if (pairTokenBalance > burnPoolAmount) {296296                // treasury pool297297                super._update(mainPair, treasuryAddress, treasuryAmount);298298                // reward pool

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/ngp_2025_09 \
    --patch worked_example/ngp_2025_09/controls/non_repair__cosmetic_rename/Token.sol \
    --backend local --sha256

Expected output: core 153930c934f39d21979946035a2a16110da3f564cc12b10f83165601c7b6a977 and strict 5fd319bfccdc26dd07ef1cf7f4cb75281547b69969082a3392fd2a3eb5a9fff1.

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

Control note

from the repository

A source change with no semantic effect. The PoC itself is the control here: the exploit still succeeds, so no security obligation is needed to reject it.

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