CVE-2018-13734

Vulnerability

The mintToken function in the AZTToken Ethereum smart contract (and related contracts in the GEMCHAIN repository [1][2]) contains an integer overflow vulnerability. The function does not perform a bounds check before updating a user's balance, allowing the contract owner to mint an arbitrary number of tokens to any address. This flaw affects the AZTToken implementation as deployed and described in the referenced EtherTokens repository [2].

Exploitation

An attacker who is the contract owner can call mintToken with a large mintedAmount value that causes an integer overflow when added to the target address's existing balance. The owner does not require any special privileges beyond contract ownership, which is typically controlled by the address that deployed the contract [1][2]. The exploitation can be performed directly via a transaction, with no user interaction needed.

Impact

A successful overflow allows the owner to inflate the token supply or assign an arbitrarily high balance to any account, effectively stealing tokens or manipulating the contract's token economy. This can lead to complete loss of token value for legitimate holders, as the owner can create tokens out of thin air [1]. The attacker's ability to set balances to any value violates the expected integrity of the token's supply.

Mitigation

No fix has been published for the AZTToken contract referenced in the repository [2]. The vulnerability exists in the original code, and as of the publication date (2018-07-09), no patched version is available. Token holders should treat any contract using the vulnerable mintToken pattern as untrustworthy. The only effective mitigation is to avoid using or relying on the affected contract [1][2].