smart contract security

7 Smart Contract Security Threats You Need to Know About

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Blockchain technology has ushered in a new era of trust-minimized environments where assets and transactions can be exchanged freely without any centralized authority, but the freedom and flexibility of blockchain come with risk. To ensure your contracts are secure, it’s essential to know about the most common security threats that can compromise your blockchain system and what to do about them. Here are seven smart contract security threats you need to know about and ways to avoid them.

51% attack

A 51% attack is when a single miner or group of miners controls more than 50% of the network’s mining hash rate, giving them the power to confirm transactions on the network. This could allow them to double spend coins, prevent other transactions from being confirmed, and more. While it’s unlikely that a 51% attack would happen on a major cryptocurrency like Bitcoin, it’s still something to be aware of.

Race condition

A race condition is when two or more processes are trying to access the same resource at the same time, and the order in which they access it matters. If left unchecked, race conditions can lead to all sorts of problems, like data corruption, deadlocks, and livelocks. To avoid these issues, be sure to design your smart contracts with concurrency in mind.

Out-of-gas bug

The out-of-gas bug is one of the most common smart contract security threats. It occurs when a transaction runs out of gas before it is complete. This can cause the transaction to fail and can lead to a loss of funds. To avoid this, always check the gas limit before sending a transaction and ensure it is high enough to cover the entire transaction.

Unchecked send() calls bug

One of the most common smart contract security threats is the unchecked send() call bug. This can happen when a developer forgets to check if a transfer of value has been completed before moving on with code execution. This can result in a loss of funds for the sender or receiver.

Access Control bug

A big security threat when it comes to smart contracts is the access control bug. This is when a contract fails to properly restrict access to certain functions, meaning that anyone can call them. This can lead to all sorts of problems, like someone being able to delete your entire contract or change the price of an item in your store. To avoid this, you need to be very careful about who has access to your smart contracts and ensure that only the people who absolutely need it have access.

Replay attacks

A replay attack is when a hacker captures and re-transmits a valid transaction to the blockchain, resulting in the execution of the same transaction twice. This can be used to double-spend cryptocurrency, for example. To prevent replay attacks, you can use a mechanism like a nonce, which is a number that can only be used once.

Wallet reuse bug

One of the most common smart contract security threats is the wallet reuse bug. This occurs when a user tries to reuse their wallet address across multiple contracts. While this may seem like a convenient way to save time, it can actually lead to some serious security issues. If one of the contracts you’re using is compromised, all of your funds could be at risk.


The biggest takeaway from this research is that security audits are essential for all blockchain system users. If a developer is truly interested in making their smart contract free from vulnerabilities, they need to be aware of these security threats, and it is likely necessary for them to conduct independent security audits. Developers who launch smart contracts without a security audit risk users funds, so it’s in developers’ best interests to make sure their smart contract is secure before it goes live.

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M.I Kani
M.I Kani

Mahmoud is a web3 developer and security researcher. His expertise includes blockchain and cybersecurity. The topics he writes about include blockchain, metaverse, web3, cyber threats, and security defenses, as well as research and innovation in information security.

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