CVE-2018-13518 in Tcash
Summary
by MITRE
The mintToken function of a smart contract implementation for TCash, 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.
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 02/27/2020
The vulnerability identified as CVE-2018-13518 represents a critical integer overflow flaw within the mintToken function of TCash Ethereum token smart contract implementation. This vulnerability resides in the core token minting mechanism that allows contract owners to create new tokens and distribute them to users. The flaw manifests when the mintToken function processes token minting operations without proper overflow checks, creating a scenario where arithmetic operations can exceed the maximum representable value for the data type being used. Such overflow conditions typically occur when the sum of existing balances and newly minted tokens surpasses the maximum value that can be stored in the target data type, causing the value to wrap around to zero or a negative value. The vulnerability directly impacts the tokenomics and security model of TCash, as it grants the contract owner unprecedented control over user balances.
The technical exploitation of this vulnerability stems from improper input validation and arithmetic handling within the smart contract's mintToken function. When the contract owner invokes this function with specific parameters, the underlying integer arithmetic fails to account for potential overflow conditions that occur during balance updates. This type of vulnerability maps directly to CWE-190, which specifically addresses integer overflow and unsigned integer overflow conditions, and aligns with CWE-682, which covers incorrect arithmetic operations. The vulnerability operates at the core level of the contract's state management, where user balances are maintained in storage variables that are susceptible to manipulation through unchecked arithmetic operations. The lack of overflow protection in the mintToken function creates a pathway for malicious or accidental manipulation of token distributions, potentially allowing contract owners to manipulate user balances to arbitrary values.
The operational impact of CVE-2018-13518 extends beyond simple balance manipulation to potentially compromise the entire token economy and user trust within the TCash ecosystem. An attacker with contract ownership privileges could exploit this vulnerability to inflate user balances to extremely high values, potentially causing cascading failures in the token's economic model. The vulnerability also enables the creation of tokens with negative balances or zero balances when overflow conditions are triggered, fundamentally breaking the expected behavior of token transfers and accounting. This flaw could lead to unauthorized token distribution, manipulation of token prices, or complete disruption of the token's functionality. The attack surface is particularly concerning as it directly affects the fundamental principle of decentralized token management, where users expect their balances to be accurately maintained and protected from unauthorized modification.
Mitigation strategies for CVE-2018-13518 must address the root cause through comprehensive code review and implementation of proper overflow protection mechanisms. The primary remediation involves adding overflow checks using require statements or SafeMath libraries that prevent arithmetic operations from exceeding data type limits. Smart contract developers should implement comprehensive input validation for all parameters passed to mintToken functions, ensuring that balance calculations remain within valid integer ranges. The solution should also incorporate proper access control measures to limit who can invoke mintToken operations, reducing the attack surface for privilege escalation. Organizations should implement rigorous testing procedures including formal verification and automated testing tools to identify similar integer overflow conditions in other contract functions. Additionally, the vulnerability highlights the importance of adhering to established security standards and best practices such as those outlined in the Solidity security guidelines, which recommend using SafeMath libraries and implementing comprehensive overflow protection for all arithmetic operations. The remediation process should include thorough auditing of all contract functions that perform arithmetic operations, particularly those that modify state variables, to ensure similar vulnerabilities are not present in other parts of the contract implementation.