Blur Finance Exchange

Smart Contract Security Assessment

October 21, 2022

SUMMARY​

ABSTRACT​

Dedaub was commissioned to perform a security audit of the Blur Protocol.

Two earlier versions of the protocol had already been audited by Dedaub in June 2022. The corresponding reports can be found here (v1.0) and here (v1.1).

The Blur protocol consists of a decentralized NFT Exchange which supports the exchange of ERC721 tokens for ETH or WETH.

Traders sign and submit orders off-chain through the Blur web application. Orders can be submitted as single orders or in bulk, by providing appropriate signatures.

The BlurExchange contract provides functionality which allows the matching of a sell order and a buy order, committing the trade on-chain. The caller of this functionality can thus cause the automatic transfer of the NFTs and WETH from one party to the other. On the other hand, the transfer of the NFTs for ETH requires the buyer to match the orders.

An order can be submitted with or without an expiration time set. In the latter case, the order will become invalid once a certain block range set by the exchange is exceeded, or when the user has requested his off-chain oracle to stop providing authorisation signatures.

Orders may be canceled at any time by specifying the order to be canceled, or a number of orders to be canceled. The exchange also supports the facility of canceling all of a user's orders by incrementing the user’s nonce.

A PolicyManager contract allows matching policies to be whitelisted by the Blur team. This provides extensibility by specifying the conditions under which a buy and a sell order can be matched by the exchange contract. Currently, only one matching policy is available.

The ExecutionDelegate contract performs the transfer of assets between the buyer and the seller that was mentioned above. Only contracts approved by the Blur team are able to execute this functionality. In addition, users can revoke permission from the ExecutionDelegate to perform transfers on their behalf at any time.

This audit report covers the contracts of the at-the-time private repository blur-io/contracts-snapshot-not-public of the Blur protocol, at commit hash 8c8b62ab9e8b94f9ffc6027813af8571af1b9beb.

Two auditors worked on the codebase for 7 days.

The full audited contract list is the following:

SETTING & CAVEATS​

The audit’s main target is security threats, i.e., what the community understanding would likely call "hacking", rather than the regular use of the protocol. Functional correctness (i.e. issues in "regular use") is a secondary consideration. Typically it can only be covered if we are provided with unambiguous (i.e. full-detail) specifications of what is the expected, correct behaviour. In terms of functional correctness, we often trusted the code’s calculations and interactions, in the absence of any other specification. Functional correctness relative to low-level calculations (including units, scaling and quantities returned from external protocols) is generally most effectively done through thorough testing rather than human auditing.

VULNERABILITIES & FUNCTIONAL ISSUES​

This section details issues affecting the functionality of the contract. Dedaub generally categorizes issues according to the following severities, but may also take other considerations into account such as impact or difficulty in exploitation:

Issue resolution includes “dismissed” or “acknowledged” but no action taken, by the client, or “resolved”, per the auditors.

CRITICAL SEVERITY​

[No critical severity issues]

HIGH SEVERITY​

MEDIUM SEVERITY​

[No medium severity issues]

LOW SEVERITY​

[No low severity issues]

OTHER / ADVISORY ISSUES​

This section details issues that are not thought to directly affect the functionality of the project, but we recommend considering them.

function _efficientHash(bytes32 a, bytes32 b) private pure
returns (bytes32 value) {
  assembly {
    mstore(x00, a)
    mstore(x20, b)
    value := keccak256(x00, x40)
  }
}

DISCLAIMER​

The audited contracts have been analyzed using automated techniques and extensive human inspection in accordance with state-of-the-art practices as of the date of this report. The audit makes no statements or warranties on the security of the code. On its own, it cannot be considered a sufficient assessment of the correctness of the contract. While we have conducted an analysis to the best of our ability, it is our recommendation for high-value contracts to commission several independent audits, a public bug bounty program, as well as continuous security auditing and monitoring through Dedaub Security Suite.

ABOUT DEDAUB​

Dedaub offers significant security expertise combined with cutting-edge program analysis technology to secure some of the most prominent protocols in DeFi. The founders, as well as many of Dedaub's auditors, have a strong academic research background together with a real-world hacker mentality to secure code. Protocol blockchain developers hire us for our foundational analysis tools and deep expertise in program analysis, reverse engineering, DeFi exploits, cryptography and financial mathematics.