CVE-2021-33403 in Token
Summary
by MITRE • 08/04/2021
An integer overflow in the transfer function of a smart contract implementation for Lancer Token, an Ethereum ERC20 token, allows the owner to cause unexpected financial losses between two large accounts during a transaction.
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Analysis
by VulDB Data Team • 08/07/2021
The vulnerability identified as CVE-2021-33403 represents a critical integer overflow flaw within the Lancer Token smart contract implementation on the Ethereum blockchain. This issue specifically manifests within the transfer function of the ERC20 token contract, where improper handling of integer arithmetic creates a condition that can be exploited by the contract owner to manipulate transaction outcomes. The vulnerability stems from the contract's failure to properly validate or constrain integer values during mathematical operations, particularly when dealing with large account balances or transfer amounts that exceed the maximum representable value for the data type being used. Such integer overflow conditions are classified under CWE-190, which specifically addresses integer overflow and underflow issues in software systems.
The technical exploitation of this vulnerability occurs when the contract owner deliberately initiates transactions involving accounts with substantial balances, where the arithmetic operations in the transfer function exceed the maximum value that can be stored in the designated integer data type. This overflow condition results in the wrapping of values back to the minimum representable value, creating unexpected financial discrepancies between accounts. The impact is particularly severe because it allows for the unauthorized transfer of funds or manipulation of account balances in ways that can cause significant financial loss to token holders. The vulnerability directly relates to the fundamental security principle of input validation and proper arithmetic boundary checking in smart contract development, which is essential for maintaining the integrity of decentralized financial systems.
From an operational perspective, this vulnerability presents a substantial risk to token holders and the broader Ethereum ecosystem, as it enables the contract owner to cause unexpected financial losses during transaction processing. The attack vector is particularly concerning because it requires no external intervention beyond the owner's ability to initiate transactions, making it an internal threat that can be exploited without requiring additional privileges or external attack surfaces. The financial implications extend beyond simple fund loss, as such vulnerabilities can erode trust in the token ecosystem and potentially affect the reputation of the entire project. This type of vulnerability aligns with ATT&CK technique T1548.001, which covers abuse of cloud compute resources, as the exploitation can be performed through legitimate contract operations that leverage the underlying blockchain infrastructure. The impact on system integrity is severe, as it undermines the fundamental assumption that blockchain transactions will behave predictably and according to established mathematical principles.
Mitigation strategies for this vulnerability require immediate contract auditing and redeployment of fixed implementations that properly handle integer arithmetic operations. The recommended approach involves implementing explicit bounds checking and overflow protection mechanisms within the transfer function, utilizing safe arithmetic libraries or compiler features that prevent integer overflow conditions. Smart contract developers should implement comprehensive testing procedures including boundary value analysis and stress testing with large numerical inputs to identify potential overflow scenarios. Additionally, the contract should incorporate proper error handling that prevents execution when arithmetic operations would result in invalid states, and implement checks that validate all input parameters against expected ranges. The solution must align with established security standards for blockchain development and should be verified through independent security audits to ensure that similar vulnerabilities are not present in other mathematical operations within the contract. This vulnerability underscores the critical importance of formal verification techniques and rigorous security testing in smart contract development, as outlined in industry best practices for secure blockchain application development.