ecexit - eccentricexit - Updates to Inflation Multiplier on L2 can undone by anyone via OOG + replay.

[sherlock-admin]

ecexit

high

eccentricexit - Updates to Inflation Multiplier on L2 can undone by anyone via OOG + replay.

Summary

The protocol governs governs the inflation multiplier on the L2EcoBridge contract via an L1 to L2 message. An adversary can craft a transaction with just enough gas so that when it reaches the L2 it runs out of gas at the proper moment. Then, when favorable, they can replay this message to update the inflation multiplier to an old value.

Vulnerability Detail

The behavior is as following:

1. The adversary (Alice) calls L1ECOBridge.rebase(). This initiates an L1 to L2 message that will write the current inflationMultiplier to L2EcoBridge.inflationMultiplier. She passes a large enough _l2Gas to the call such that it enters L2ECOBridge.rebase function, but small enough that it reverts there due to Out Of Gas (OOG) error:

    function rebase(uint256 _inflationMultiplier)
        external
        virtual
        onlyFromCrossDomainAccount(l1TokenBridge)
        validRebaseMultiplier(_inflationMultiplier)
    {
        inflationMultiplier = _inflationMultiplier; // revert due to OOG in this scope;
        l2Eco.rebase(_inflationMultiplier);
        emit RebaseInitiated(_inflationMultiplier);
    }

L2ECOBridge.rebase

3. The call then returns to L2CrossDomainMessenger.relayMessage and it marks that transaction (tx1) as failed:

        ...
        bool success = SafeCall.call(_target, gasleft() - RELAY_RESERVED_GAS, _value, _message);
        xDomainMsgSender = Constants.DEFAULT_L2_SENDER;

        if (success) {
            successfulMessages[versionedHash] = true;
            emit RelayedMessage(versionedHash);
        } else {
            failedMessages[versionedHash] = true; // Tx marked as replayable.
            ...
        }
        ...

4. Things continue operating normally. Inflation multiplier is updated L1 ECO token 1 or N times, people call L1ECOBridge.rebase with enough gas, keeping the L2 up to date.

5. Alice doesn't like the current inflation multiplier so she sends a transaction to L2CrossDomainMessenger.relayMessage to replay her old tx1 transaction. This time, she provides enough gas such that the execution completes, reverting the inflation multiplier to the old value.

Impact

An adversary can effectively DoS updates to the inflation multiplier indefinitely and benefit from the broken, inconsistent state.

Code Snippet

Tool used

Manual Review

Recommendation

Disallow in the contract passing a too low l2Gas to L1ECOBridge.rebase.

Duplicate of #142

[eccentricexit]

Escalate for 10 USDC

This is not the same issue reported on number #52, but it is a duplicate of the already recognized issue #142 so it should receive a reward.

[sherlock-admin]

Escalate for 10 USDC

This is not the same issue reported on number #52, but it is a duplicate of the already recognized issue #142 so it should receive a reward.

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[nknavkal]

This issue is a duplicate of #142

[hrishibhat]

Escalation accepted

Valid duplicate of #142

[sherlock-admin]

Escalation accepted

Valid duplicate of #142

This issue's escalations have been accepted!

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