Smart Contract Security: Common Solidity Vulnerabilities

Overview

Ethereum smart contracts are immutable programs deployed on the blockchain. While this guarantees trustless execution, it also means that vulnerabilities cannot be patched after deployment. The Ethereum Foundation highlights several recurring security issues that developers must understand before deploying Solidity contracts.

Reentrancy

Reentrancy vulnerabilities occur when a contract calls an external address before updating its internal state. Attackers can exploit this by re-entering the function multiple times, potentially draining funds. This flaw was responsible for the infamous DAO hack.

Mitigation:

Use the checks-effects-interactions pattern and avoid external calls inside critical logic.

Integer Overflow and Underflow

In early Solidity versions, arithmetic operations could silently overflow or underflow, leading to incorrect balances or logic errors. Modern Solidity versions revert by default, but developers can still introduce risk through unchecked arithmetic.

Mitigation:

Avoid unchecked blocks unless absolutely necessary and validate numeric inputs.

Access Control Issues

Improper access control can allow unauthorized users to execute sensitive functions, such as withdrawing funds or modifying ownership. Many exploits result from missing or incorrect permission checks.

Mitigation:

Use strict role-based access control and thoroughly audit all privileged functions.

Final Thoughts

Security is a fundamental requirement in Ethereum development. The Ethereum Foundation strongly recommends thorough testing, code reviews, and third-party audits before deploying smart contracts to production networks.