CVE-2018-13752 in Thread
Summary
by MITRE
The mintToken function of a smart contract implementation for Thread, 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 • 03/03/2020
The vulnerability identified in CVE-2018-13752 represents a critical integer overflow flaw within the mintToken function of an Ethereum-based smart contract implementation for the Thread token. This vulnerability stems from improper input validation and arithmetic handling within the smart contract code, creating a scenario where the contract owner can manipulate user balances arbitrarily. The flaw exists in the core token minting mechanism that should logically restrict balance modifications to authorized parties while maintaining proper arithmetic boundaries.
The technical implementation of this vulnerability manifests through an integer overflow condition that occurs when the mintToken function processes balance updates. When the contract attempts to increment a user's token balance, the arithmetic operation exceeds the maximum value that can be represented by the underlying data type, causing the value to wrap around to zero or a negative value. This overflow condition is particularly dangerous because it allows the contract owner to bypass normal balance constraints and directly manipulate account balances through crafted inputs. The vulnerability is classified under CWE-190 as an integer overflow condition, specifically involving signed integer overflow that leads to unexpected behavior in the token distribution mechanism.
The operational impact of this vulnerability extends beyond simple balance manipulation to encompass complete control over the token economy and user accounts. An attacker with access to the contract owner's private key can effectively drain user balances, create unlimited tokens, or manipulate the total supply to gain unfair advantages. This represents a fundamental breach of trust in the token system and could result in significant financial losses for users who hold Thread tokens. The vulnerability also affects the integrity of the blockchain ledger, as it allows for the creation of false transaction records and potentially undermines the immutability guarantees that smart contracts are designed to provide.
The exploitation of this vulnerability aligns with several tactics described in the MITRE ATT&CK framework for smart contract security, particularly those involving privilege escalation and data manipulation. Attackers can leverage this flaw to perform unauthorized balance modifications, effectively creating a backdoor that allows them to manipulate the token distribution without detection. The vulnerability also enables potential denial of service scenarios where user balances can be set to zero, rendering accounts unusable and effectively locking users out of their funds. Organizations and users should implement immediate mitigations including contract audits, balance verification mechanisms, and the deployment of patched versions with proper integer overflow protections.
Mitigation strategies for this vulnerability require comprehensive code review and implementation of proper boundary checks within the mintToken function. Smart contract developers must ensure that all arithmetic operations include overflow and underflow protections using modern solidity practices such as SafeMath libraries or explicit overflow checks. The contract owner should implement additional access controls and transaction monitoring to detect unauthorized balance manipulations. Furthermore, regular security audits and formal verification techniques should be employed to identify similar vulnerabilities in smart contract implementations. The fix typically involves adding validation checks before balance updates and ensuring that the integer operations are performed within safe boundaries that prevent overflow conditions from occurring.