Browse public reportsMars4 Shoot ERC-20 Security Review
Executive Summary
This security review was prepared by Quantstamp, the leader in blockchain security.
- Shih-Hung Wang Auditing Engineer
Summary of Findings
Quantstamp conducted a security review for the ShootERC20 token developed in the Mars Battle project.
The ShootERC20 token slightly modifies the ERC-20 standard contract written by OpenZeppelin. Upon creation, the ShootERC20 contract mints a fixed number of 1_000_000_000 tokens to the contract deployer. The ShootERC20 holders can transfer or approve another address to transfer their tokens, the same as a typical ERC-20 token. Additionally, the ShootERC20 holders can burn an arbitrary number of their tokens up to their entire balance. As there is no further minting of the token after the contract creation, the total supply of ShootERC20 can only decrease through time when a user burns their token.
All issues included in this report are informational in severity. MS-1 and MS-2 point out this project needs more documentation and tests. MS-3 points out a best practice of smart contract development. MS-4 describes a well-known issue of ERC-20 tokens, and MS-5 describes a concern about locked funds in the contract.
Although the additions to the base ERC-20 contract are minimal, the project has no tests, so the changes are not covered. Quantstamp, as always, strongly recommends adding tests to safeguard against unpredictable code. All issues in this report are considered acknowledged.
| ID | Description | Severity | Status |
|---|---|---|---|
| MS-1 | Token Holders Can Burn Their Tokens | Informational The issue does not post an immediate risk, but is relevant to security best practices or Defence in Depth. | Acknowledged |
| MS-2 | Lack of Specification and Test Suite | Informational The issue does not post an immediate risk, but is relevant to security best practices or Defence in Depth. | Acknowledged |
| MS-3 | Unlocked Pragma | Informational The issue does not post an immediate risk, but is relevant to security best practices or Defence in Depth. | Acknowledged |
| MS-4 | Allowance Double-Spend Exploit | Informational The issue does not post an immediate risk, but is relevant to security best practices or Defence in Depth. | Acknowledged |
| MS-5 | Accidentally Transferred Funds to the Contract Are Locked | Informational The issue does not post an immediate risk, but is relevant to security best practices or Defence in Depth. | Acknowledged |
Assessment Breakdown
Quantstamp's objective was to evaluate the repository for security-related issues, code quality, and adherence to specification and best practices.
Only features that are contained within the repositories at the commit hashes specified on the front page of the report are within the scope of the audit and fix review. All features added in future revisions of the code are excluded from consideration in this report.
Possible issues we looked for included (but are not limited to):
- Transaction-ordering dependence
- Timestamp dependence
- Mishandled exceptions and call stack limits
- Unsafe external calls
- Integer overflow / underflow
- Number rounding errors
- Reentrancy and cross-function vulnerabilities
- Denial of service / logical oversights
- Access control
- Centralization of power
- Business logic contradicting the specification
- Code clones, functionality duplication
- Gas usage
- Arbitrary token minting
Methodology
- Code review that includes the following
- Review of the specifications, sources, and instructions provided to Quantstamp to make sure we understand the size, scope, and functionality of the smart contract.
- Manual review of code, which is the process of reading source code line-by-line in an attempt to identify potential vulnerabilities.
- Comparison to specification, which is the process of checking whether the code does what the specifications, sources, and instructions provided to Quantstamp describe.
- Testing and automated analysis that includes the following:
- Test coverage analysis, which is the process of determining whether the test cases are actually covering the code and how much code is exercised when we run those test cases.
- Symbolic execution, which is analyzing a program to determine what inputs cause each part of a program to execute.
- Best practices review, which is a review of the smart contracts to improve efficiency, effectiveness, clarity, maintainability, security, and control based on the established industry and academic practices, recommendations, and research.
- Specific, itemized, and actionable recommendations to help you take steps to secure your smart contracts.
Scope
The scope is the deployed contract at address 0xbc61e13ca6830fc7f035fd0e90a01cd08be6dcaa on Ethereum.
Files Included
ShootERC20.sol
Findings
MS-1 Token Holders Can Burn Their Tokens
File(s) affected: ShootERC20.sol
Description: The ShootERC20 contract has a public burn() function, which allows the token holders to burn an arbitrary number of their tokens up to their entire balance. As high-level documentation or code comments for the project are not presented, the intention of such a design choice needs to be clarified. This issue is to note that users and third-party developers need to know that such a public burn() function exists.
Recommendation: Consider clarifying the design choice of a public burn() function in user documentation.
MS-2 Lack of Specification and Test Suite
File(s) affected: ShootERC20.sol
Description: Although the ShootERC20 is a typical ERC-20 token with an additional self-burning feature, it is still recommended to document the use cases of the ERC-20 token, either in the code comments or on a public-facing website. For example, document each role in the system and the expected behavior or possible actions for each role.
Additionally, it is recommended that a test suite for smart contracts be developed before they are used in production. The test suite's branch coverage should be at least 90%.
Recommendation: Consider adding specifications, documents, and tests to the project to improve the overall quality and maintainability.
MS-3 Unlocked Pragma
File(s) affected: ShootERC20.sol
Description: The ShootERC20 contract specifies in the header a version number of the format pragma solidity ^0.8.0; The caret (^) before the version number implies an unlocked pragma, meaning that the compiler may use the specified version and above, hence the term "unlocked".
Recommendation: It is recommended that the caret be removed and the file be locked onto a specific Solidity version for consistency and to prevent using a version not tested during development.
Consider using the latest Solidity version, v0.8.25, at the time of writing for contracts deployed on Ethereum. For other EVM chains, an older version, e.g., v0.8.19, can be used to be compatible with them.
MS-4 Allowance Double-Spend Exploit
File(s) affected: ShootERC20.sol
Description: As it is currently constructed, the ShootERC20 contract is vulnerable to the ERC-20 allowance double-spend exploit, as are most of the known ERC-20 tokens.
Exploit Scenario:
1. Alice allows Bob to transfer N amount of Alice's tokens (N>0) by calling the approve() function on the token smart contract, passing Bob's address and N as the function arguments.
- After some time, Alice decides to change from
NtoM(M>0) the number of Alice's tokens Bob is allowed to transfer, so she calls theapprove()function again, this time passing Bob's address andMas function arguments. - Bob notices Alice's second transaction before it is mined and quickly sends another transaction that calls the
transferFrom()function to transferNAlice's tokens somewhere. - If Bob's transaction is executed before Alice's transaction, then Bob will successfully transfer
NAlice's tokens and will be able to transfer anotherMtoken. - Before Alice notices any irregularities, Bob calls the
transferFrom()function again to transferMAlice's tokens.
Recommendation: This is a well-known issue with ERC-20 tokens. We recommend that developers of applications dependent on approve() of ERC-20 tokens remember to set the allowance to 0 first and verify if it was used before setting the new value.
On the other hand, the exploit as described above can be mitigated through the use of functions that increase or decrease the allowance relative to its current value, such as increaseAllowance() and decreaseAllowance(), which are supported by the ShootERC20 contract.
MS-5 Accidentally Transferred Funds to the Contract Are Locked
File(s) affected: ShootERC20.sol
Description: As a typical ERC-20 token, the ShootERC20 contract does not have a particular function to retrieve funds accidentally transferred to itself. As a result, these accidentally transferred funds will be locked in the contract.
Recommendation: Consider whether this issue should be addressed. If so, consider allowing a contract owner to retrieve funds accidentally transferred to the contract. However, this approach will introduce a privileged role and increase the contract's centralization risks.
Definitions
- High severity – High-severity issues usually put a large number of users' sensitive information at risk, or are reasonably likely to lead to catastrophic impact for client's reputation or serious financial implications for client and users.
- Medium severity – Medium-severity issues tend to put a subset of users' sensitive information at risk, would be detrimental for the client's reputation if exploited, or are reasonably likely to lead to moderate financial impact.
- Low severity – The risk is relatively small and could not be exploited on a recurring basis, or is a risk that the client has indicated is low impact in view of the client's business circumstances.
- Informational – The issue does not post an immediate risk, but is relevant to security best practices or Defence in Depth.
- Undetermined – The impact of the issue is uncertain.
- Fixed – Adjusted program implementation, requirements or constraints to eliminate the risk.
- Mitigated – Implemented actions to minimize the impact or likelihood of the risk.
- Acknowledged – The issue remains in the code but is a result of an intentional business or design decision. As such, it is supposed to be addressed outside the programmatic means, such as: 1) comments, documentation, README, FAQ; 2) business processes; 3) analyses showing that the issue shall have no negative consequences in practice (e.g., gas analysis, deployment settings).
Appendix
File Signatures
The following are the SHA-256 hashes of the reviewed files. A file with a different SHA-256 hash has been modified, intentionally or otherwise, after the security review. You are cautioned that a different SHA-256 hash could be (but is not necessarily) an indication of a changed condition or potential vulnerability that was not within the scope of the review.
Files
fe6...3a7 ./ShootERC20.solfe607954b9b45d924a29dada40f143602d0e7338869b2c3547c6f2dd0dbf13a7
Automated Analysis
N/AChangelog
- 2024-04-12 - Final report
About Quantstamp
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Mars4 Shoot ERC-20 Security Review