Lucky9io Lottery Smart Contract Vulnerability: Exploitable Random Number Generation and Currency Unit Misconfiguration

CVE-2018-17071 · MEDIUM Severity

AV:N/AC:L/AU:N/C:P/I:N/A:N

The fallback function of a simple lottery smart contract implementation for Lucky9io, an Ethereum gambling game, generates a random value with the publicly readable variable entry_number. This variable is private, yet it is readable by eth.getStorageAt function. Also, attackers can purchase a ticket at a low price by directly calling the fallback function with small msg.value, because the developer set the currency unit incorrectly. Therefore, it allows attackers to always win and get rewards.

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