CVE-2021-34273 in BTC2X
Summary
by MITRE • 08/04/2021
A security flaw in the 'owned' function of a smart contract implementation for BTC2X (B2X), a tradeable Ethereum ERC20 token, allows attackers to hijack victim accounts and arbitrarily increase the digital supply of assets.
Be aware that VulDB is the high quality source for vulnerability data.
Analysis
by VulDB Data Team • 08/07/2021
The vulnerability identified as CVE-2021-34273 resides within the smart contract implementation of BTC2X (B2X), an Ethereum-based ERC20 token that represents a tradeable asset. This flaw specifically impacts the 'owned' function of the contract, which is designed to manage account ownership and asset distribution. The vulnerability demonstrates a critical weakness in the contract's access control mechanisms that directly undermines the security model of the token and its underlying blockchain infrastructure.
The technical flaw manifests through improper handling of account ownership states within the smart contract's 'owned' function. Attackers can exploit this vulnerability to hijack victim accounts by manipulating the contract's internal state management. The flaw enables unauthorized individuals to assume control of legitimate user accounts, effectively bypassing the intended ownership verification processes. This type of vulnerability aligns with CWE-284 Access Control Issues, where insufficient access control mechanisms allow unauthorized users to perform privileged operations. The exploitation occurs through careful manipulation of the contract's state variables, particularly those related to account ownership and asset allocation.
The operational impact of this vulnerability extends beyond simple account hijacking to include the arbitrary inflation of digital assets within the system. Once attackers gain control of victim accounts, they can manipulate the contract to increase the total supply of BTC2X tokens without proper authorization. This creates a scenario where the digital asset supply becomes inflated, potentially leading to significant economic disruption and loss of value for legitimate token holders. The vulnerability represents a fundamental breach in the token's supply mechanism, allowing attackers to essentially mint additional tokens beyond the intended distribution parameters.
The attack vector for this vulnerability involves leveraging the contract's insufficient state validation during ownership transitions. Attackers can craft specific transaction sequences that exploit the lack of proper access control checks within the 'owned' function. This approach aligns with ATT&CK technique T1078 Valid Accounts, where adversaries use compromised credentials or unauthorized access to gain system privileges. The vulnerability also demonstrates characteristics of T1499 Endpoint Denial of Service, as the exploitation can potentially disrupt normal contract operations and asset management functions. Security researchers have noted that this type of vulnerability is particularly dangerous in decentralized finance applications where asset integrity and account security are paramount.
Mitigation strategies for CVE-2021-34273 require immediate contract auditing and code review to identify all instances where account ownership states are manipulated without proper authorization checks. The recommended approach involves implementing comprehensive access control mechanisms that verify account ownership before allowing any state modifications. This includes adding proper validation checks within the 'owned' function to ensure that only authorized parties can perform ownership transfers or supply adjustments. Additionally, the contract should implement proper event logging and monitoring systems to detect unauthorized access attempts. Industry best practices suggest adopting formal verification methods and conducting thorough security audits before deploying smart contracts to production environments. The vulnerability highlights the importance of following secure coding practices as outlined in the OWASP Smart Contract Security Verification Standard, particularly regarding access control and state management validation.