CVE-2018-13488 in Crypto Alley Shares
Summary
by MITRE
The mintToken function of a smart contract implementation for Crypto Alley Shares (CAST), 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 • 02/27/2020
The vulnerability identified in CVE-2018-13488 represents a critical integer overflow flaw within the mintToken function of the Crypto Alley Shares (CAST) smart contract deployed on the Ethereum blockchain. This vulnerability stems from improper input validation and arithmetic operations that fail to account for the maximum limits of integer data types. The smart contract implementation lacks proper bounds checking mechanisms, creating a condition where an attacker can manipulate the token supply and user balances through carefully crafted transactions. The vulnerability directly impacts the integrity of the token economy and the trustworthiness of the contract's accounting system. The issue manifests when the mintToken function processes user inputs without verifying that the resulting balance values remain within the valid integer range, allowing for wraparound behavior that can be exploited to manipulate token holdings.
The technical exploitation of this vulnerability follows a well-defined pattern that aligns with CWE-190, which specifically addresses integer overflow and underflow conditions in software implementations. When the owner of the contract invokes the mintToken function with malicious parameters, the arithmetic operations involved in balance calculations can exceed the maximum value that can be represented by the underlying integer type. This overflow condition results in the balance value wrapping around to a much smaller number or even zero, creating a scenario where arbitrary user balances can be manipulated to any desired value. The vulnerability is particularly dangerous because it allows the contract owner to potentially inflate or deflate user balances, effectively enabling unauthorized minting or destruction of tokens. The flaw exists at the core of the contract's token management logic, where the mintToken function does not implement proper overflow detection mechanisms that would prevent such arithmetic anomalies from occurring.
The operational impact of this vulnerability extends beyond simple financial manipulation to encompass broader security implications for the entire token ecosystem. Users who hold CAST tokens face potential loss of their holdings as malicious actors could exploit this vulnerability to set their balances to zero or manipulate their token amounts to gain unfair advantages. The vulnerability undermines the fundamental principles of blockchain security and trustless transactions, as it allows for unauthorized balance modifications that violate the immutable nature of blockchain records. Additionally, the exploitability of this vulnerability means that the entire token distribution could be compromised, potentially leading to significant financial losses for token holders and damaging the reputation of the project. The attack surface is further expanded because the vulnerability affects the contract owner's ability to maintain proper control over token distribution, creating potential for both accidental and intentional manipulation of the token economy.
Mitigation strategies for CVE-2018-13488 should focus on implementing comprehensive input validation and arithmetic overflow protection mechanisms within the smart contract code. The recommended approach involves incorporating explicit bounds checking and using safe arithmetic libraries that prevent integer overflow conditions. The contract should validate all input parameters to ensure they remain within acceptable ranges before performing any balance calculations. Additionally, implementing proper access controls and audit trails can help detect unauthorized attempts to exploit the vulnerability. Organizations should consider upgrading to newer smart contract frameworks that include built-in overflow protection mechanisms and follow security best practices established by industry standards such as the Ethereum Smart Contract Security Best Practices. The vulnerability also highlights the importance of thorough code review processes and formal verification techniques that can identify such critical flaws before deployment. According to ATT&CK framework category TA0005 (Defense Evasion) and TA0004 (Privilege Escalation), this vulnerability represents a significant vector for attackers to gain unauthorized access and manipulate system resources, making it essential for security teams to implement robust monitoring and response procedures. The remediation process should include not only fixing the immediate overflow condition but also conducting comprehensive security audits of all contract functions to prevent similar issues from emerging in other parts of the codebase.