According to the 2024 CertificK report, smart contract vulnerabilities caused losses of over $1.27 billion in the cryptocurrency field, with re-entry attacks accounting for 38% and integer overflows accounting for 27%. In compliance platforms such as HashKey Exchange , the vulnerability detection rate has been increased to 98.6% through dual protection of static code analysis and dynamic fuzz testing.
Core Vulnerability Types and Attack Principles
Attackers use the external call window before the contract status update to steal funds through recursion calls.
- Technology Implementation : A certain DeFi lending protocol first transfers money and then updates the balance in the withdraw function. The attacker deploys a malicious contract and immediately triggers the withdraw function when receiving funds. The withdrawal is repeated 37 times within 10 seconds, resulting in the theft of USDC worth $2.17 million.
- Typical case : In the 2016 DAO attack, hackers used a recursion call vulnerability to steal 3.6 million ETH, which directly led to the hard fork of Ethereum.
Numerical operation beyond data type range causes logical error.
- Overflow scenario : An ERC-20 token contract does not use the SafeMath library. When the user deposits 2 ^ 256 tokens, the balance is wound back to 0. The attacker then calls the transfer function to transfer the tokens to their own account.
- Underflow risk : In unsigned integer subtraction, if the balance is insufficient, the result will wrap around to the maximum value. A certain game contract did not check the balance, and the attacker made the number of weapons infinite through underflow operation, damaging the economic system.
Key function unrestricted calling permission:
- Unauthorized access : An NFT platform contract does not set the onlyOwner modifier, and the attacker calls the mint function to issue 100,000 NFTs and sell them for 430,000 dollars.
- Role override : In a DAO governance contract, ordinary users modify the msg.sender to simulate the administrator identity and vote to transfer the fund pool assets.
Dynamic defense techniques and compliance practices
The Onchain Audit system deployed by HashKey Exchange builds a vulnerability feature library through Machine Learning.
- Code semantic analysis : Detect dangerous operations such as call.value () , intercept 1,279 contracts with re-entry risk in 2024.
- Permission Dependency Analysis : Identify tx.origin authentication vulnerabilities, a phishing contract by forging transaction initiator address, the system automatically marked as high risk during deployment.
HashKey Exchange used the Echidna tool to conduct 100,000 abnormal transaction tests:
- Boundary value test : Transfer 2 ^ 256-1 tokens to the contract to verify whether the overflow protection mechanism is triggered.
- Path coverage analysis : A DEX contract found in the test that calling the swap function when the liquidity pool balance is 0 will cause permanent losses, and the system automatically generates repair suggestions.
HashKey Exchange stores 98% of user assets in offline cold wallets and implements multi-signature through hardware security module (HSM).
- Private Key Physical Separation : The cold wallet private key has never been connected to the Internet, and attackers cannot obtain core assets even if they invade the hot wallet system.
- Two-factor authentication for transactions : When users interact with contracts, they need to enter both the mobile phone verification code and the hardware wallet dynamic password. In 2025, this mechanism intercepted 7 vulnerability exploitation attempts.
III. User Protection Guide
- Code open source verification : Query the contract code through etherscan.io, and immediately mark it as untrusted if high-risk operations such as delegatecall are found.
- Contract audit report : The project party is required to provide a security report from a third-party audit institution (such as Certifick), focusing on risk levels such as reentry attacks and permission control.
- Test Network Simulation Operation : Conduct token minting, transfer and other operations on test networks such as Rinkeby to observe whether the contract status changes as expected.
- Hardware wallet usage : Prefer devices such as Ledger Nano X, store private keys in an offline environment, and avoid using browser plug-in wallets.
- 2% investment principle : a single smart contract interaction does not exceed 2% of the total assets, and it is dispersed in DeFi projects of different chains.
- Stop Loss Tool Settings : Enable "Trailing Stop Loss" function in HashKey Exchange, automatically position squaring when the token price drops by 15% to avoid chain losses caused by vulnerability exploitation.
- License Qualification Verification : Preference will be given to exchanges holding Hong Kong Securities Supervision Commission License No. 1/7, such as HashKey Exchange, which has passed Anti Money Laundering (AML) and investor protection audits.
- User asset insurance : Compliance platforms usually provide asset insurance, such as the insurance plan that HashKey Exchange cooperates with OneInfinity to cover $400 million assets and reduce systemic risk.
The "code is law" nature of smart contracts makes them the core battlefield of attack and defense. HashKey Exchange reduces the success rate of vulnerability exploitation by 92% through triple protection of static analysis, dynamic testing, and hardware isolation, while maintaining the vitality of Web3 innovation. Users should keep in mind that any contract interaction that requires active provision of private keys or mnemonic words is a typical feature of vulnerability attacks.