26 Апр, 2023

Integer Overflow and Underflow(SWC-101)

Description

Smart contracts are self-executing programs that operate on a blockchain network. These programs use cryptographic algorithms to enforce the rules and regulations of the system, and are executed automatically without the need for intermediaries. One of the main challenges in developing smart contracts is ensuring that they are secure and free from vulnerabilities that could be exploited by attackers. One such vulnerability is the SWC-101 category, which is characterized by an overflow or underflow that occurs when an arithmetic operation exceeds the maximum or minimum size of a given data type.

For instance, in computer programming, a number stored in the uint8 data type is represented by an 8-bit unsigned integer that ranges from 0 to 2^8-1. If an arithmetic operation results in a value that is greater than this maximum value, an integer overflow has occurred. Similarly, if an arithmetic operation results in a value that is smaller than the minimum representable value, an integer underflow has occurred.

This type of vulnerability can have serious consequences for smart contracts, as it can lead to unexpected behavior or enable attackers to manipulate the system in unintended ways. To prevent these vulnerabilities, smart contract developers must ensure that arithmetic operations do not exceed the maximum or minimum size of the data type being used. One way to do this is by using overflow-safe arithmetic operations, which are designed to prevent integer overflows and underflows. It is crucial for smart contract developers to be aware of this vulnerability and take appropriate measures to prevent it, in order to ensure the security and reliability of smart contract systems.

Восстановление

Using safe math libraries is strongly recommended to prevent integer overflow and underflow vulnerabilities in smart contracts. Safe math libraries are vetted and tested, providing a standardized approach to perform arithmetic operations on numerical data types. By consistently using safe math libraries throughout the smart contract system, developers can ensure that all arithmetic operations are performed correctly and securely, reducing the risk of vulnerabilities. It is important to note that safe math libraries are not a silver bullet and must be used correctly. Developers should thoroughly test their smart contracts and ensure that they are properly implementing safe math libraries to avoid any potential issues.

Contract Samples

Code with a vulnerability

				
					pragma solidity ^0.4.21;
contract TokenSaleChallenge {
    mapping(address => uint256) public balanceOf;
    uint256 constant PRICE_PER_TOKEN = 1 ether;
    function TokenSaleChallenge(address _player) public payable {
        require(msg.value == 1 ether);
    }
    function isComplete() public view returns (bool) {
        return address(this).balance < 1 ether;
    }
    function buy(uint256 numTokens) public payable {
        require(msg.value == numTokens * PRICE_PER_TOKEN);
        balanceOf[msg.sender] += numTokens;
    }
    function sell(uint256 numTokens) public {
        require(balanceOf[msg.sender] >= numTokens);
        balanceOf[msg.sender] -= numTokens;
        msg.sender.transfer(numTokens * PRICE_PER_TOKEN);
    }
}

				
			

Tools for scaning SWC-101

1. Mythril: It is a popular open-source tool that can detect many types of security vulnerabilities in smart contracts, including SWC-101. Mythril can be integrated with popular development environments like Visual Studio Code and can also be used as a command-line tool.

2. Slither: It is another open-source tool that can analyze Solidity code for security vulnerabilities, including SWC-101. Slither can be integrated with popular development environments like Visual Studio Code and can also be used as a command-line tool.

3. Securify: It is a tool that can analyze Solidity code for security vulnerabilities, including SWC-101. Securify is available as a web-based tool and as a command-line tool.

4. SmartCheck: It is a cloud-based tool that can scan Solidity code for security vulnerabilities, including SWC-101. SmartCheck can be integrated with popular development environments like Visual Studio Code and can also be used as a standalone tool.

5. Oyente: It is another open-source tool that can analyze Solidity code for security vulnerabilities, including SWC-101. Oyente can be used as a command-line tool.

Общее перечисление слабых мест (CWE)

CWE-682: Неверный расчет

Mitigation for SWC-101

1. Use libraries: Libraries can be used to perform arithmetic operations, which can help avoid integer overflow and underflow vulnerabilities.

2. SafeMath: Use SafeMath libraries or similar libraries that provide safe arithmetic operations.

3. Input validation: Implement input validation checks to ensure that the values are within acceptable limits.

4. Use smaller integers: Use the smallest possible integer type that can accommodate the necessary range of values.

5. Limit the number of iterations: Limit the number of iterations in loops and other iterative structures to prevent overflow and underflow.

6. Avoid unchecked math: Avoid using the unchecked math functions, as they can cause integer overflow and underflow vulnerabilities.

7. Test and audit: Thoroughly test and audit the code to identify and fix any integer overflow and underflow vulnerabilities.

Заключение

SWC-101 is a vulnerability where a contract uses a predictable seed value for its random number generator. Attackers can exploit this by predicting the output of the generator to execute a successful attack. Mitigations include using a more secure method for generating random numbers and ensuring the seed value is unpredictable. Developers must take this vulnerability seriously and consider implementing secure random number generation schemes.

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