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Security Audit
February 22, 2024
Version 1.0.0
Presented by 0xMacro
This document includes the results of the security audit for Connext's smart contract code as found in the section titled ‘Source Code’. The security audit was performed by the Macro security team on February 22, 2024.
The purpose of this audit is to review the source code of certain Connext Solidity contracts, and provide feedback on the design, architecture, and quality of the source code with an emphasis on validating the correctness and security of the software in its entirety.
Disclaimer: While Macro’s review is comprehensive and has surfaced some changes that should be made to the source code, this audit should not solely be relied upon for security, as no single audit is guaranteed to catch all possible bugs.
The following is an aggregation of issues found by the Macro Audit team:
| Severity | Count | Acknowledged | Won't Do | Addressed |
|---|---|---|---|---|
| Low | 1 | - | - | 1 |
| Code Quality | 2 | - | 2 | - |
Connext was quick to respond to these issues.
Our understanding of the specification was based on the following sources:
The following source code was reviewed during the audit:
744573a6f3586159ff454ef4ddfba4cab6c88e9d
0074c04a8fc190768e95fc80259fb39d43201e4b
Specifically, we audited the following contracts within this repository, in the `packages/deployments/contracts/contracts/messaging/` directory:
| Source Code | SHA256 |
|---|---|
| packages/deployments/contracts/contracts/messaging/connectors/ConnectorsLib.sol |
|
| packages/deployments/contracts/contracts/messaging/connectors/scroll/BaseScroll.sol |
|
| packages/deployments/contracts/contracts/messaging/connectors/scroll/ScrollHubConnector.sol |
|
| packages/deployments/contracts/contracts/messaging/connectors/scroll/ScrollSpokeConnector.sol |
|
Click on an issue to jump to it, or scroll down to see them all.
We quantify issues in three parts:
This third part – the severity level – is a summary of how much consideration the client should give to fixing the issue. We assign severity according to the table of guidelines below:
| Severity | Description |
|---|---|
|
(C-x) Critical |
We recommend the client must fix the issue, no matter what, because not fixing would mean significant funds/assets WILL be lost. |
|
(H-x) High |
We recommend the client must address the issue, no matter what, because not fixing would be very bad, or some funds/assets will be lost, or the code’s behavior is against the provided spec. |
|
(M-x) Medium |
We recommend the client to seriously consider fixing the issue, as the implications of not fixing the issue are severe enough to impact the project significantly, albiet not in an existential manner. |
|
(L-x) Low |
The risk is small, unlikely, or may not relevant to the project in a meaningful way. Whether or not the project wants to develop a fix is up to the goals and needs of the project. |
|
(Q-x) Code Quality |
The issue identified does not pose any obvious risk, but fixing could improve overall code quality, on-chain composability, developer ergonomics, or even certain aspects of protocol design. |
|
(I-x) Informational |
Warnings and things to keep in mind when operating the protocol. No immediate action required. |
|
(G-x) Gas Optimizations |
The presented optimization suggestion would save an amount of gas significant enough, in our opinion, to be worth the development cost of implementing it. |
In the ScrollHubConnector contract, the _sendMessage() implementation tries to decode refundAddress parameter value from the _encodedData input argument. If missing then refundAddress is set to address(0).
function _sendMessage(bytes memory _data, bytes memory _encodedData) internal override checkMessageLength(_data) {
address _refundAddress = (_encodedData.length > 0) ? abi.decode(_encodedData, (address)) : address(0);
bytes memory _calldata = abi.encodeWithSelector(Connector.processMessage.selector, _data);
L1_SCROLL_MESSENGER.sendMessage{value: msg.value}(
mirrorConnector,
ZERO_MSG_VALUE,
_calldata,
gasCap,
_refundAddress
);
}
Scroll’s L1Messenger contract would use _refundAddress value to return with surplus msg.value. If this _refundAddress is address(0), those surplus native assets will be forever lost.
Remediations to consider
refundAddress is not provided within _encodedData input argument, orrefundAddress should be initialized with an address under control when it is not provided so that assets can be retrieved later.In the ScrollSpokeConnector, _sendMessage() function implementation when invoking sendMessage() on L2_SCROLL_MESSENGER provides and references gasCap storage variable from the parent GasCap contract.
function _sendMessage(bytes memory _data, bytes memory) internal override checkMessageLength(_data) {
bytes memory _calldata = abi.encodeWithSelector(Connector.processMessage.selector, _data);
L2_SCROLL_MESSENGER.sendMessage(mirrorConnector, ZERO_MSG_VALUE, _calldata, **gasCap**);
}
However, gasCap value is not used or relied upon in the L2_SCROLL_MESSENGER.sendMessage().
Therefore, consider providing a constant value of 0 instead of gasCap.
Notice natspec comment for ScrollHubConnector should refer to L2 Scroll Spoke Connector instead of L2 Scroll Hub Connector.
Scroll Hub Connector contract in charge of sending messages to the L2 Scroll ~~Hub~~Spoke Connector through the
L1 Scroll Messenger, and receiving messages from the L2 Scroll ~~Hub~~Spoke Connector through the L1 Scroll Messenger
Notice and dev natspec comments for IL1ScrollMessenger.relayMessageWithProof() are incorrect.
* @notice Execute L1 => L2 message. // replace with: Relay a L2 => L1 message with message proof.
* @dev Make sure this is only called by privileged accounts. // there are no requirements for callers to be privileged
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The scope of this report and review is limited to a review of only the code presented by the Connext team and only the source code Macro notes as being within the scope of Macro’s review within this report. This report does not include an audit of the deployment scripts used to deploy the Solidity contracts in the repository corresponding to this audit. Specifically, for the avoidance of doubt, this report does not constitute investment advice, is not intended to be relied upon as investment advice, is not an endorsement of this project or team, and it is not a guarantee as to the absolute security of the project. In this report you may through hypertext or other computer links, gain access to websites operated by persons other than Macro. Such hyperlinks are provided for your reference and convenience only, and are the exclusive responsibility of such websites’ owners. You agree that Macro is not responsible for the content or operation of such websites, and that Macro shall have no liability to your or any other person or entity for the use of third party websites. Macro assumes no responsibility for the use of third party software and shall have no liability whatsoever to any person or entity for the accuracy or completeness of any outcome generated by such software.