EVM Smart Contracts Security

Critical Severity:

1. Reentrancy Attacks:

   • Contracts allowing an attacker to re-enter a function before the previous execution completes, enabling unauthorized fund transfers.

2. Integer Overflow/Underflow:

   • Improper handling of arithmetic operations leading to unexpected behavior, such as wrapping or invalid calculation of values.

3. Authorization & Access Control:

   • Lack of proper access controls allowing unauthorized users to execute sensitive functions or modify critical data.

4. Unchecked External Calls:

   • Contracts interacting with external contracts or addresses without validating return data, leading to potential vulnerabilities.

5. Denial of Service (DoS):

   • Vulnerabilities that could allow attackers to block the contract’s functionality or make it excessively expensive to use.

High Severity:

6. Unchecked Return Values:
   • Ignoring return values of external calls, which might lead to unexpected behavior or vulnerabilities.
7. Front-Running Attacks:
   • Vulnerabilities where attackers exploit transaction ordering to their advantage, typically in decentralized finance (DeFi) applications.
8. Gas Limit & Loops:
   • Potential risks related to gas limits and excessive gas consumption due to inefficient or infinite loops.
9. Timestamp Dependence:
   • Vulnerabilities arising from the dependence on block timestamps, which can be manipulated by miners.

Medium Severity:

10. External Dependency Risks:
    • Contracts relying on external data sources or oracles without implementing proper security measures.
11. Weak Randomness Sources:
    • Using predictable or unreliable sources for randomness, which can be exploited in gaming or gambling contracts.
12. Unused Variables & Functions:
    • Unintended leftover or unused code that might have security implications or affect contract behavior.

Low Severity:

13. Documentation & Clarity:

    • Lack of comprehensive comments and documentation, making it difficult for auditors and developers to understand the contract logic.

14. Code Readability & Optimization:

    • Code that is hard to read or unnecessarily complex, potentially leading to errors or inefficiencies.

Advised practices:

1. Reentrancy Attacks:

   • Implement the "Checks-Effects-Interactions" pattern to minimize reentrancy risks.
   • Use the "withdraw pattern" where external calls are made after updating state variables.

2. Integer Overflow/Underflow:

   • Use SafeMath libraries or in-built language features to prevent arithmetic vulnerabilities.
   • Perform boundary checks and ensure data types are suitable to prevent overflows/underflows.

3. Authorization & Access Control:

   • Use access control mechanisms like role-based permissions or whitelisting.
   • Implement proper authentication and authorization checks for sensitive functions.

4. Unchecked External Calls:

   • Validate return data from external calls and use checks to handle failures.
   • Use known and audited external contracts and interfaces wherever possible.

5. Denial of Service (DoS):

   • Limit gas consumption and utilize gas stipends judiciously.
   • Implement circuit breakers or limits on repetitive or expensive operations.

6. Unchecked Return Values:

   • Always check and handle return values from external calls.
   • Use error handling mechanisms to prevent unexpected behavior.

7. Front-Running Attacks:

   • Implement measures like commit-reveal schemes or random ordering to mitigate front-running.
   • Use time locks or delay mechanisms for critical transactions.

8. Gas Limit & Loops:

   • Optimize contract logic to avoid gas-intensive operations.
   • Implement gas limits and use loop guards to prevent infinite loops.

9. Timestamp Dependence:

   • Use block numbers or other secure sources instead of relying solely on timestamps.
   • Implement mechanisms that are resistant to manipulation based on block timestamps.

10. External Dependency Risks:

    • Use trusted and decentralized oracles for external data sources.
    • Implement multiple data sources and consensus mechanisms for critical decisions.

11. Weak Randomness Sources:

    • Use secure and decentralized sources for generating random numbers.
    • Implement verifiable randomness or commit-reveal schemes.

12. Unused Variables & Functions:

    • Conduct regular code reviews and remove any unused or deprecated code.
    • Document reasons for unused code and ensure it's not vulnerable if present.

13. Documentation & Clarity:

    • Maintain comprehensive and clear documentation explaining contract functionality and interactions.
    • Use standardized naming conventions and comments for improved readability.

14. Code Readability & Optimization:

    • Write clean, modular, and well-commented code to enhance readability.
    • Optimize contract code for efficiency and cost-effectiveness where possible.

Also check out:

https://immunefi.com/immunefi-top-10/

https://samczsun.com/the-dangers-of-surprising-code/