CVE-2018-13670 in GFCB
Summary
by MITRE
The mintToken function of a smart contract implementation for GFCB, an Ethereum token, has an integer overflow that allows the owner of the contract to set the balance of an arbitrary user to any value.
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Analysis
by VulDB Data Team • 02/28/2020
The vulnerability identified in CVE-2018-13670 represents a critical integer overflow flaw within the mintToken function of the GFCB Ethereum token smart contract implementation. This vulnerability resides in the core token management functionality where the contract owner can manipulate user balances through a mathematical overflow condition. The flaw occurs when the mintToken function processes token minting operations without proper overflow checks, allowing an attacker with owner privileges to execute malicious operations that can arbitrarily set user balances to predetermined values. This type of vulnerability falls under CWE-190, which specifically addresses integer overflow and underflow conditions, making it a fundamental security issue in smart contract development. The vulnerability is particularly dangerous because it directly impacts the token's integrity and can be exploited to create unlimited tokens or manipulate user holdings.
The technical execution of this vulnerability involves the smart contract's inability to validate input parameters during the mintToken function call, particularly when dealing with large numerical values that exceed the maximum capacity of the underlying data types. When the contract attempts to increment a token balance or perform arithmetic operations on user balances, the integer overflow causes the value to wrap around to an unexpected result, enabling the contract owner to bypass normal balance limitations. This behavior aligns with ATT&CK technique T1059.006 for smart contract manipulation and represents a direct violation of the expected tokenomics principles. The vulnerability can be exploited through direct function calls to the mintToken method with carefully crafted parameters that trigger the overflow condition, allowing the owner to set any user's balance to any desired value including zero, maximum values, or negative balances depending on the specific implementation details.
The operational impact of this vulnerability extends beyond simple balance manipulation to potentially compromise the entire token economy and user trust in the system. An attacker with owner access can manipulate token distributions, create artificial scarcity, or even drain the token supply by setting balances to zero for other users. This flaw undermines the fundamental principles of blockchain tokenomics and can lead to significant financial losses for token holders. The vulnerability also creates a pathway for potential denial of service attacks where legitimate users might be unable to access their tokens due to manipulated balances. From a compliance standpoint, this vulnerability could violate regulatory requirements for transparent and fair token distribution mechanisms, particularly in jurisdictions that require proper accounting and audit trails for digital assets. The impact is further amplified because Ethereum smart contracts are immutable by design, meaning that once deployed with this vulnerability, the flaw cannot be easily corrected without creating a new contract.
Mitigation strategies for this vulnerability require immediate implementation of proper integer overflow checks within the smart contract code, specifically within the mintToken function and any other functions that perform arithmetic operations on token balances. The recommended approach involves using safe math libraries such as OpenZeppelin's SafeMath or implementing explicit overflow checks before any arithmetic operations. Additionally, the contract should implement proper access control mechanisms to ensure that only authorized parties can execute mintToken operations, and all balance modifications should be logged for audit purposes. The vulnerability highlights the importance of thorough code review processes and automated security testing for smart contracts, particularly when dealing with financial applications. Organizations should also implement proper testing procedures including unit tests, integration tests, and formal verification methods to identify similar vulnerabilities before deployment. Regular security audits and continuous monitoring of smart contract behavior are essential to maintain the integrity of token systems and prevent exploitation of similar mathematical overflow vulnerabilities.